text: Study of Earth's magnetosphere began in 1600, when William Gilbert discovered that the magnetic field on the surface of Earth resembled that on a terrella, a small, magnetized sphere. In the 1940s, Walter M. Elsasser proposed the model of dynamo theory, which attributes Earth's magnetic field to the motion of  Earth's iron outer core. Through the use of magnetometers, scientists were able to study the variations in Earth's magnetic field as functions of both time and latitude and longitude. Beginning in the late 1940s, rockets were used to study cosmic rays. In 1958, Explorer 1, the first of the Explorer series of space missions, was launched to study the intensity of cosmic rays above the atmosphere and measure the fluctuations in this activity. This mission observed the existence of the Van Allen radiation belt (located in the inner region of Earth's magnetosphere), with the Explorer 3 mission later that year definitively proving its existence. Also in 1958, Eugene Parker proposed the idea of the solar wind. The term 'magnetosphere' was proposed by Thomas Gold in 1959. The Explorer 12 mission (1961) led to the observation by Cahill and Amazeen in 1963 of a sudden decrease in the strength of the magnetic field near the noon meridian, later named the magnetopause. In 1983, the International Cometary Explorer observed the magnetotail, or the distant magnetic field.

text: Study of Earth's magnetosphere began in 1600, when

entity_name: William Gilbert (astronomer)

text: William Gilbert

text: discovered that the magnetic field on the surface of Earth resembled that on a

entity_name: Terrella

text: terrella

text: , a small, magnetized sphere. In the 1940s,

entity_name: Walter M. Elsasser

text: Walter M. Elsasser

text: proposed the model of

entity_name: Dynamo theory

text: dynamo theory

text: , which attributes

entity_name: Earth's magnetic field

text: Earth's magnetic field

text: to the motion of  Earth's

entity_name: Iron

text: iron

entity_name: Outer core

text: outer core

text: . Through the use of

entity_name: Magnetometer

text: magnetometer

text: s, scientists were able to study the variations in Earth's magnetic field as functions of both time and latitude and longitude. Beginning in the late 1940s, rockets were used to study

entity_name: Cosmic ray

text: cosmic rays

text: . In 1958,

entity_name: Explorer 1

text: Explorer 1

text: , the first of the Explorer series of space missions, was launched to study the intensity of cosmic rays above the atmosphere and measure the fluctuations in this activity. This mission observed the existence of the

entity_name: Van Allen radiation belt

text: Van Allen radiation belt

text: (located in the inner region of Earth's magnetosphere), with the

entity_name: Explorer 3

text: Explorer 3

text: mission later that year definitively proving its existence. Also in 1958,

entity_name: Eugene Parker

text: Eugene Parker

text: proposed the idea of the

entity_name: Solar wind

text: solar wind

text: . The term 'magnetosphere' was proposed by

entity_name: Thomas Gold

text: Thomas Gold

text: in 1959. The Explorer 12 mission (1961) led to the observation by Cahill and Amazeen in 1963 of a sudden decrease in the strength of the magnetic field near the noon meridian, later named the

entity_name: Magnetopause

text: magnetopause

text: . In 1983, the

entity_name: International Cometary Explorer

text: International Cometary Explorer

text: observed the magnetotail, or the distant magnetic field.

method: UNH-ecn

text: Magnetofossils are not only being studied for their paleoenvironmental or paleoclimatic indicators.  As mentioned above, magnetofossils hold a remanent magnetization when they are formed.  That is, the magnetite (or greigite) aligns in the direction of the geomagnetic field.  The magnetite crystals can be thought of as being a simple magnet with a north and south pole, this north-south orientation aligns with the north-south magnetic poles of the Earth.  These fossils are then buried within the rock record.  Researchers can examine these rock samples in a remanent magnetometer where the effects of Earth's current magnetic field is removed, to determine the remanent, or initial, magnetization of the rock sample when it was formed.  In knowing the orientation of the rock in-situ and the remanent magnetization, researchers can determine the Earth's geomagnetic field at the time the rock was formed.  This can be used as an indicator of magnetic field direction, or reversals in the Earth's magnetic field, where the Earth's north and south magnetic poles switch (which happen on average every 450,000 years).

text: Magnetofossils are not only being studied for their paleoenvironmental or paleoclimatic indicators.  As mentioned above, magnetofossils hold a remanent magnetization when they are formed.  That is, the magnetite (or greigite) aligns in the direction of the geomagnetic field.  The magnetite crystals can be thought of as being a simple magnet with a north and south pole, this north-south orientation aligns with the north-south magnetic poles of the Earth.  These fossils are then buried within the rock record.  Researchers can examine these rock samples in a remanent

text: magnetometer

text: where the effects of Earth's current magnetic field is removed, to determine the remanent, or initial, magnetization of the rock sample when it was formed.  In knowing the orientation of the rock in-situ and the remanent magnetization, researchers can determine the Earth's geomagnetic field at the time the rock was formed.  This can be used as an indicator of magnetic field direction, or

entity_name: Geomagnetic reversal

text: reversals in the Earth's magnetic field

text: , where the Earth's north and south magnetic poles switch (which happen on average every 450,000 years).

text: ). If this is the case the permanent magnet will be magnetized in the direction of the field inside the solenoid. Applying the same pulse of current in the opposite direction will lead to magnetize the magnet in the opposite direction. Therefore, we have the same behavior as when we mechanically rotate the magnet. This configuration is the concept of electropermanent magnet: Using a pulse of current we reverse the magnetization direction of one of the magnets and we will turn ON and OFF the external magnetic field.

method: ICT-DRMMTKS

text: In step 2, since there is no current observed, one might conclude that the magnetic field did not rotate with the rotating magnet. (Whether it does or does not effectively or relatively, the Lorentz force is zero since v is zero relative to the laboratory frame. So there is no current measuring from laboratory frame.) The use of the Lorentz equation to explain this paradox has led to a debate in the literature as to whether or not a magnetic field rotates with a magnet. Since the force on charges expressed by the Lorentz equation depends upon the relative motion of the magnetic field (i.e. the laboratory frame) to the conductor where the EMF is located it was speculated that in the case when the magnet rotates with the disk but a voltage still develops, the magnetic field (i.e. the laboratory frame) must therefore not rotate with the magnetic material (of course since it is the laboratory frame), while the effective definition of magnetic field frame or the "effective/relative rotation of the field" turns with no relative motion with respect to the conductive disk.

text: In

entity_name: Faraday paradox

entity_section: The procedure

text: step 2

method: Bert-ConvKNRM

text: As each bump in the wheel approaches the pickup, it temporarily concentrates the magnetic field near it, and thus strengthens the magnetic field that passes through the coil, inducing a current in the coil by the process of Electromagnetic induction.  As the bump moves past, this concentrating effect is reduced again, the magnetic field weakens slightly, and an opposite current is induced in the coil.  Thus, the frequency of the current in the coil depends on the speed of rotation of the disk and the number of bumps.

text: As each bump in the wheel approaches the pickup, it temporarily concentrates the magnetic field near it, and thus strengthens the magnetic field that passes through the coil, inducing a current in the coil by the process of

entity_name: Electromagnetic induction

text: Electromagnetic induction

text: .  As the bump moves past, this concentrating effect is reduced again, the magnetic field weakens slightly, and an opposite current is induced in the coil.  Thus, the frequency of the current in the coil depends on the speed of rotation of the disk and the number of bumps.

text: The neodymium atom also can have a large magnetic dipole moment because it has 7 unpaired electrons in its electron structure as opposed to about 3 in iron.  In a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field.  This gives the NdFeB compound a high saturation magnetization (J ~1.6 T or 16 kG) and typically 1.3 teslas.  Therefore, as the maximum energy density is proportional to J, this magnetic phase has the potential for storing large amounts of magnetic energy (BH ~ 512 kJ/m or 64 MG·Oe). This magnetic energy value is about 18 times greater than "ordinary" magnets by volume. This property is higher in NdFeB alloys than in samarium cobalt (SmCo) magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the magnetic properties of neodymium magnets depend on the alloy composition, microstructure, and manufacturing technique employed.

text: The neodymium atom also can have a large

entity_name: Magnetic moment

text: magnetic dipole moment

text: because it has 7

entity_name: Unpaired electron

text: unpaired electron

text: s in its electron structure as opposed to about 3 in

text: iron

text: .  In a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field.  This gives the NdFeB compound a high

entity_name: Saturation (magnetic)

text: saturation magnetization

text: (J ~1.6

entity_name: Tesla (unit)

text: T

text: or 16

entity_name: Gauss (unit)

text: kG

text: ) and typically 1.3 teslas.  Therefore, as the maximum energy density is proportional to J, this magnetic phase has the potential for storing large amounts of magnetic energy (BH ~ 512 kJ/m or 64

entity_name: Oersted

entity_section: Stored energy

text: MG·Oe

text: ). This magnetic energy value is about 18 times greater than "ordinary" magnets by volume. This property is higher in NdFeB alloys than in

entity_name: Samarium–cobalt magnet

text: samarium cobalt

text: (SmCo) magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the magnetic properties of neodymium magnets depend on the alloy composition, microstructure, and manufacturing technique employed.

text: Scientific opinion is divided on what causes geomagnetic excursions.  The dominant theory is that they are an inherent aspect of the dynamo processes that maintain the Earth's magnetic field.  In computer simulations, it is observed that magnetic field lines can sometimes become tangled and disorganized through the chaotic motions of liquid metal in the Earth's core.  In such cases, this spontaneous disorganization can cause decreases in the magnetic field as perceived at the Earth's surface.  In truth, under this scenario, the Earth's magnetic field intensity does not significantly change in the core itself, but rather energy is transferred from a dipole configuration to higher order multipole moments which decay more rapidly with the distance from the Earth's core, so that the expression of such a magnetic field at the surface of the Earth would be considerably less, even without significant changes in the strength of the deep field.  This scenario is supported by observed tangling and spontaneous disorganizations in the solar magnetic field.  However, this process in the sun invariabily leads to a reversal of the solar magnetic field (see: solar cycle), and has never been observed such that the field would recover without large scale changes in field orientation.

entity_name: Opinion

entity_section: Scientific opinion

text: Scientific opinion

text: is divided on what causes geomagnetic excursions.  The dominant theory is that they are an inherent aspect of the

text: dynamo

text: processes that maintain the Earth's magnetic field.  In computer simulations, it is observed that magnetic field lines can sometimes become tangled and disorganized through the chaotic motions of liquid metal in the

entity_name: Earth

entity_section: The core

text: Earth's core

text: .  In such cases, this spontaneous disorganization can cause decreases in the magnetic field as perceived at the Earth's surface.  In truth, under this scenario, the Earth's magnetic field intensity does not significantly change in the core itself, but rather energy is transferred from a

entity_name: Dipole

text: dipole

text: configuration to higher order

entity_name: Multipole expansion

text: multipole moment

text: s which decay more rapidly with the distance from the Earth's core, so that the expression of such a magnetic field at the surface of the Earth would be considerably less, even without significant changes in the strength of the deep field.  This scenario is supported by observed tangling and spontaneous disorganizations in the

entity_name: Sun

text: solar

text: magnetic field.  However, this process in the sun invariabily leads to a reversal of the solar magnetic field (see:

entity_name: Solar cycle

text: solar cycle

text: ), and has never been observed such that the field would recover without large scale changes in field orientation.

text: In order to reduce the size and weight of the magnet of the magnetic sail, it may be possible to inflate the magnetic field using a plasma in the same way that the plasma around the Earth stretches out the Earth's magnetic field in the magnetosphere. In this approach, called mini-magnetospheric plasma propulsion (M2P2), currents that run through the plasma will augment and partially replace the currents in the coil. This is expected to be especially useful far from the Sun, where the increased effective size of a M2P2 sail compensates for the reduced dynamic pressure of the solar wind. The original NASA design proposes a spacecraft containing a can-shaped electromagnet into which a plasma is injected. The plasma pressure stretches the magnetic field and inflates a bubble of plasma around the spacecraft. The plasma then generates a kind of miniaturized magnetosphere around the spacecraft, analogous to the magnetosphere that surrounds the Earth. The protons and electrons which make up the solar wind are deflected by this magnetosphere and the reaction accelerates the spacecraft. The thrust of the M2P2 device would be steerable to some extent, potentially allowing the spacecraft to 'tack' into the solar wind and allowing efficient changes of orbit.

text: In order to reduce the size and weight of the

entity_name: Magnet

text: magnet

text: of the magnetic sail, it may be possible to inflate the magnetic field using a plasma in the same way that the plasma around the Earth stretches out the Earth's magnetic field in the

entity_name: Magnetosphere

text: magnetosphere

text: . In this approach, called mini-magnetospheric plasma propulsion (M2P2), currents that run through the plasma will augment and partially replace the currents in the coil. This is expected to be especially useful far from the Sun, where the increased effective size of a M2P2 sail compensates for the reduced dynamic pressure of the solar wind. The original

entity_name: NASA

text: NASA

text: design proposes a spacecraft containing a can-shaped electromagnet into which a plasma is injected. The

entity_name: Plasma (physics)

text: plasma

text: pressure stretches the magnetic field and inflates a bubble of plasma around the spacecraft. The plasma then generates a kind of miniaturized magnetosphere around the spacecraft, analogous to the

text: magnetosphere

text: that surrounds the Earth. The protons and electrons which make up the

text: solar wind

text: are deflected by this magnetosphere and the reaction accelerates the spacecraft. The thrust of the M2P2 device would be steerable to some extent, potentially allowing the spacecraft to 'tack' into the solar wind and allowing efficient changes of orbit.

text: Since green sea turtles migrate long distances during breeding seasons, they have special adaptive systems in order to navigate. In the open ocean, the turtles navigate using wave directions, sun light, and temperatures. The sea turtles also contain an internal magnetic compass. They can detect magnetic information by using magnetic forces acting on the magnetic crystals in their brains. Through these crystals, they can sense the intensity Earth’s magnetic field and are able to make their way back to their nesting grounds or preferred feeding grounds.

text: Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence  have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility).The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect. Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because thermal motion causes the spins to become randomly oriented without it. Thus the total magnetization will drop to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnets is non-linear and much stronger, so that it is easily observed, for instance, in magnets on one's refrigerator.

text: Paramagnetism is a form of

entity_name: Magnetism

text: magnetism

text: which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence  have a relative magnetic permeability greater than

entity_name: 1 (number)

text: one

text: (or, equivalently, a positive

entity_name: Magnetic susceptibility

text: magnetic susceptibility

text: ).The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect. Unlike

entity_name: Ferromagnetism

text: ferromagnets

text: , paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because

entity_name: Kinetic theory of gases

text: thermal motion

text: causes the spins to become randomly oriented without it. Thus the total magnetization will drop to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnets is non-linear and much stronger, so that it is easily observed, for instance, in magnets on one's refrigerator.

text: A steel-hulled ship can be degaussed (more correctly, de-oerstedted or depermed) using a special degaussing station that contains many large coils and induces a magnetic field in the hull with alternating current to demagnetize the hull. This is a rather problematic solution, as magnetic compasses need recalibration and all metal objects must be kept in exactly the same place. Ships slowly regain their magnetic field as they travel through the Earth's magnetic field, so the process has to be repeated every six months.

text: A steel-hulled ship can be

entity_name: Degaussing

text: degaussed

text: (more correctly, de-oerstedted or

text: depermed

text: ) using a special degaussing station that contains many large coils and induces a magnetic field in the hull with alternating current to demagnetize the hull. This is a rather problematic solution, as magnetic compasses need recalibration and all metal objects must be kept in exactly the same place. Ships slowly regain their magnetic field as they travel through the Earth's magnetic field, so the process has to be repeated every six months.

method: dangnt-nlp

text: The first technical facilities were in the new magnetic area (the 200 area).  This area was in the middle of the woods, and remained so up until the Lab's demise in 1994. It is believed that the area was selected because it was magnetically neutral - there was less iron in the earth than in other areas to interfere with sensitive magnetic experiments.  The buildings were made of wood, with wooden pegs instead of nails. The buildings had unusual names: Bldg 203 was the "Spherical Field Lab", Building 204 was the "Long Field Lab".

text: The first technical facilities were in the new

text: magnet

text: ic area (the 200 area).  This area was in the middle of the woods, and remained so up until the Lab's demise in 1994. It is believed that the area was selected because it was magnetically neutral - there was less

text: iron

text: in the earth than in other areas to interfere with sensitive magnetic experiments.  The buildings were made of wood, with wooden pegs instead of nails. The buildings had unusual names: Bldg 203 was the "Spherical Field Lab", Building 204 was the "Long Field Lab".

text: The electrons around a nucleus will circulate in a magnetic field and create a secondary induced magnetic field. This field opposes the applied field as stipulated by Lenz's law and atoms with higher induced fields (i.e., higher electron density) are therefore called shielded, relative to those with lower electron density. The chemical milieu of an atom can influence its electron density through the polar effect. Electron-donating alkyl groups, for example, lead to increased shielding while electron-withdrawing substituents such as nitro groups lead to deshielding of the nucleus. Not only substituents cause local induced fields. Bonding electrons can also lead to shielding and deshielding effects. A striking example of this are the pi bonds in benzene. Circular current through the hyperconjugated system causes a shielding effect at the molecule's center and a deshielding effect at its edges. Trends in chemical shift are explained based on the degree of shielding or deshielding.

text: The electrons around a nucleus will circulate in a magnetic field and create a secondary

entity_name: Inductive effect

text: induced magnetic field

text: . This field opposes the applied field as stipulated by

entity_name: Lenz's law

text: Lenz's law

text: and atoms with higher induced fields (i.e., higher electron density) are therefore called shielded, relative to those with lower electron density. The chemical milieu of an atom can influence its electron density through the

entity_name: Polar effect

text: polar effect

text: . Electron-donating

entity_name: Alkyl

text: alkyl

text: groups, for example, lead to increased shielding while electron-withdrawing substituents such as

entity_name: Nitro compound

text: nitro groups

text: lead to deshielding of the nucleus. Not only substituents cause local induced fields. Bonding electrons can also lead to shielding and deshielding effects. A striking example of this are the

entity_name: Pi bond

text: pi bonds

text: in

entity_name: Benzene

text: benzene

text: . Circular current through the

entity_name: Hyperconjugation

text: hyperconjugated

text: system causes a shielding effect at the molecule's center and a deshielding effect at its edges. Trends in chemical shift are explained based on the degree of shielding or deshielding.

text: The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It consists of a degree and order 12 spherical harmonic expansion of the magnetic potential of the geomagnetic main field generated in the Earth’s core. Apart from the 168 spherical-harmonic "Gauss" coefficients, the model also has an equal number of spherical-harmonic Secular-Variation (SV) coefficients predicting the temporal evolution of the field over the upcoming five-year epoch. WMM is the standard geomagnetic model of the United States Department of Defense (DoD), the Ministry of Defence (United Kingdom), the North Atlantic Treaty Organization (NATO), and the World Hydrographic Office (WHO) navigation and attitude/heading reference.  It is also used widely in civilian navigation systems. For example, WMM is pre-installed in Android and iOS devices to correct for the magnetic declination.   The WMM is produced by the U.S. National Geophysical Data Center (NGDC) in collaboration with the British Geological Survey (BGS). The model, associated software, and documentation are distributed by the National Geophysical Data Center (NGDC) on behalf of National Geospatial-Intelligence Agency (NGA). Updated model coefficients are released at 5-year intervals, with the current model (WMM2015) expiring on December 31, 2019.  The current World Magnetic Model (WMM2015) has been released on NGDC website on Dec 15, 2014.

text: The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It consists of a degree and order 12

entity_name: Spherical harmonics

text: spherical harmonic

text: expansion of the

entity_name: Magnetic potential

text: magnetic potential

text: of the geomagnetic main field generated in the Earth’s core. Apart from the 168 spherical-harmonic "Gauss" coefficients, the model also has an equal number of spherical-harmonic Secular-Variation (SV) coefficients predicting the temporal evolution of the field over the upcoming five-year epoch. WMM is the standard geomagnetic model of the

entity_name: United States Department of Defense

text: United States Department of Defense

text: (DoD), the

entity_name: Ministry of Defence (United Kingdom)

text: Ministry of Defence (United Kingdom)

text: , the

entity_name: NATO

text: North Atlantic Treaty Organization

text: (NATO), and the

text: World Hydrographic Office

text: (WHO) navigation and attitude/heading reference.  It is also used widely in civilian navigation systems. For example, WMM is pre-installed in Android and iOS devices to correct for the

entity_name: Magnetic declination

text: magnetic declination

text: .   The WMM is produced by the U.S. National Geophysical Data Center (NGDC) in collaboration with the British Geological Survey (BGS). The model, associated software, and documentation are distributed by the

entity_name: National Geophysical Data Center

text: National Geophysical Data Center

text: (NGDC) on behalf of

entity_name: National Geospatial-Intelligence Agency

text: National Geospatial-Intelligence Agency

text: (NGA). Updated model coefficients are released at 5-year intervals, with the current model (WMM2015) expiring on December 31, 2019.  The current World Magnetic Model (WMM2015) has been released on NGDC website on Dec 15, 2014.

text: There are two methods of underwater geolocation that PSATs employ.  The first method is through light based geolocation which uses the length of the day and a noon time calculation to estimate the tags location while underwater.  This method has a functional depth limitation of light penetration which can be as shallow as a few meters to upwards of hundreds of meters.  Geolocation estimates based on light are usually coupled with additional satellite data like sea surface temperature or other available data input such as bathymetry, land avoidance, and physical limitations of the tagged animal.  The other method available is through measuring ambient light and the Earth's magnetic field. This method has a functional depth limitation equivalent of the maximum depth limitation, generally 1800m.  Magnetic based geolocation is generally not coupled with additional satellite data or other inputs, and relies on the Earth magnetic field for latitude estimations and light (noon time) for longitude estimations.

text: There are two methods of underwater geolocation that PSATs employ.  The first method is through light based geolocation which uses the length of the day and a noon time calculation to estimate the tags location while underwater.  This method has a functional depth limitation of light penetration which can be as shallow as a few meters to upwards of hundreds of meters.  Geolocation estimates based on light are usually coupled with additional satellite data like sea surface temperature or other available data input such as bathymetry, land avoidance, and physical limitations of the tagged animal.  The other method available is through measuring ambient light and the

text: Earth's magnetic field

text: . This method has a functional depth limitation equivalent of the maximum depth limitation, generally 1800m.  Magnetic based geolocation is generally not coupled with additional satellite data or other inputs, and relies on the Earth magnetic field for latitude estimations and light (noon time) for longitude estimations.

text: In regards to the magnetic field hypothesis, there are three main concepts that should be considered. The concepts include electromagnetic induction, magnetic field chemical reactions, and magnetite. In regards to electromagnetic induction, it is assumed that the sea turtles have electroreceptors. Although evidence has been found in other species such as rays and sharks, no evidence has shown that there are electroreceptors in sea turtles making this hypothesis invalid. A second concept  from the experimentation by Irwin involves chemical reactions which is commonly found  in a variety of species of newts and birds. The strength of the magnetic field affects the chemical reactions within the bodies of the newts and birds. The final concept includes the magnetic crystals that form during the magnetic pulses from the earth’s magnetic fields. These magnetic crystals formed by magnetite give the turtles directional information and guides in migration. The magnetite affects the cells of the nervous system of the sea turtle by producing a signal that references the forces of the magnetic field and the direction and magnitude that is applied. If this magnetite is used in the migration, when the earth’s magnetic poles reverse at the dipole moment, they signal that the sea turtle nervous system receives will change the migration direction. Regardless of the hypothesis, hatchling turtles have the ability to determine the direction and inclination angle of which they are swimming with aide from magnetic fields

text: Magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout a section. The samples are analyzed to determine their detrital remanent magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. For sedimentary rocks, this is possible because, when very fine-grained magnetic minerals (< 17 μm), behave like tiny compasses as they fall through the water column and orient themselves with Earth's magnetic field. Upon burial, that orientation is preserved.  For volcanic rocks, magnetic minerals, which form in the melt, orient themselves with the ambient magnetic field, and are fixed in place upon crystallization of the lava.

text: Magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout a section. The samples are analyzed to determine their detrital

text: remanent

text: magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. For sedimentary rocks, this is possible because, when very fine-grained magnetic minerals (< 17

text: μm

text: ), behave like tiny compasses as they fall through the water column and orient themselves with

text: Earth's magnetic field

text: . Upon burial, that orientation is preserved.  For volcanic rocks, magnetic minerals, which form in the melt, orient themselves with the ambient magnetic field, and are fixed in place upon crystallization of the lava.

text: A geomagnetic storm is a temporary disturbance of the Earth's Magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The increase in solar wind pressure compresses the magnetosphere and the solar wind's magnetic field interacts with the Earth’s magnetic field to transfer increased energy into the magnetosphere.  Both interactions increase plasma movement through the magnetosphere (driven by increased electric fields) and an increase in electric current in the magnetosphere and ionosphere.

text: A geomagnetic storm is a temporary disturbance of the Earth's

text: Magnetosphere

text: caused by a

text: solar wind

text: shock wave and/or cloud of magnetic field that interacts with the

text: Earth's magnetic field

text: . The increase in solar wind pressure compresses the magnetosphere and the solar wind's magnetic field interacts with the Earth’s magnetic field to transfer increased energy into the magnetosphere.  Both interactions increase plasma movement through the magnetosphere (driven by increased electric fields) and an increase in electric current in the magnetosphere and ionosphere.

text: The drag force can be used to the electrodynamic system's advantage, however, as it creates a varying force in the rails that can be used as a reactionary system to drive the train, without the need for a separate reaction plate, as in most linear motor systems. Laithwaite led development of such "traverse-flux" systems at his Imperial College laboratory. Alternatively, propulsion coils on the guideway are used to exert a force on the magnets in the train and make the train move forward. The propulsion coils that exert a force on the train are effectively a linear motor: an alternating current through the coils generates a continuously varying magnetic field that moves forward along the track. The frequency of the alternating current is synchronized to match the speed of the train. The offset between the field exerted by magnets on the train and the applied field creates a force moving the train forward.

text: Homing pigeons can use magnetic fields as part of their complex navigation system. William Keeton showed that time-shifted homing pigeons are unable to orient themselves correctly on a clear, sunny day which is attributed to time-shifted pigeons being unable to compensate accurately for the movement of the sun during the day. Conversely, time-shifted pigeons released on overcast days navigate correctly. This led to the hypothesis that under particular conditions, homing pigeons rely on magnetic fields to orient themselves. Further experiments with magnets attached to the backs of homing pigeons demonstrated that disruption of the bird’s ability to sense the Earth's magnetic field leads to a loss of proper orientation behavior under overcast conditions. There have been two mechanisms implicated in homing pigeon magnetoreception : the visually mediated free-radical pair mechanism and a magnetite based directional compass or inclination compass.  More recent behavioral tests have shown that pigeons are able to detect magnetic anomalies of 186 microtesla (1.86 Gauss).

text: Homing

text: pigeons can use magnetic fields as part of their complex

text: navigation

text: system.

text: William Keeton

text: showed that time-shifted homing pigeons are unable to orient themselves correctly on a clear, sunny day which is attributed to time-shifted pigeons being unable to compensate accurately for the movement of the sun during the day. Conversely, time-shifted pigeons released on overcast days navigate correctly. This led to the hypothesis that under particular conditions, homing pigeons rely on magnetic fields to orient themselves. Further experiments with magnets attached to the backs of homing pigeons demonstrated that disruption of the bird’s ability to sense the Earth's magnetic field leads to a loss of proper orientation behavior under overcast conditions. There have been two mechanisms implicated in homing pigeon magnetoreception : the visually mediated free-radical pair mechanism and a magnetite based directional compass or inclination compass.  More recent behavioral tests have shown that pigeons are able to detect magnetic anomalies of 186

text: microtesla

text: Gauss

text: A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth’s magnetosphere to the Earth's high latitude ionosphere. In the Earth’s magnetosphere, the currents are driven by the solar wind and interplanetary magnetic field and by bulk motions of plasma through the magnetosphere (convection indirectly driven by the interplanetary environment). The strength of the Birkeland currents changes with activity in the magnetosphere (e.g. during substorms).  Small scale variations in the upward current sheets (downward flowing electrons) accelerate magnetospheric electrons which, when they reach the upper atmosphere, create the Auroras Borealis and Australis. In the high latitude ionosphere (or auroral zones), the Birkeland currents close through the region of the auroral electrojet, which flows perpendicular to the local magnetic field in the ionosphere.  The Birkeland currents occur in two pairs of field-aligned current sheets.  One pair extends from noon through the dusk sector to the midnight sector.  The other pair extends from noon through the dawn sector to the midnight sector.  The sheet on the high latitude side of the auroral zone is referred to as the Region 1 current sheet and the sheet on the low latitude side is referred to as the Region 2 current sheet.

text: A Birkeland current is a set of currents that flow along

text: geomagnetic

text: field lines connecting the Earth’s

text: magnetosphere

text: to the Earth's high latitude

text: ionosphere

text: . In the Earth’s magnetosphere, the currents are driven by the

text: solar wind

text: and

text: interplanetary magnetic field

text: and by bulk motions of plasma through the magnetosphere (convection indirectly driven by the interplanetary environment). The strength of the Birkeland currents changes with activity in the magnetosphere (e.g. during

text: substorm

text: s).  Small scale variations in the upward current sheets (downward flowing electrons) accelerate magnetospheric electrons which, when they reach the upper atmosphere, create the

text: Auroras

text: Borealis and Australis. In the high latitude ionosphere (or auroral zones), the Birkeland currents close through the region of the auroral

text: electrojet

text: , which flows perpendicular to the local magnetic field in the ionosphere.  The Birkeland currents occur in two pairs of field-aligned current sheets.  One pair extends from noon through the dusk sector to the midnight sector.  The other pair extends from noon through the dawn sector to the midnight sector.  The sheet on the high latitude side of the auroral zone is referred to as the Region 1 current sheet and the sheet on the low latitude side is referred to as the Region 2 current sheet.

text: A gyrocompass, employed for navigation of seagoing vessels, finds the geometric north. It does so, not by sensing the Earth's magnetic field, but by using inertial space as its reference. The outer casing of the gyrocompass device is held in such a way that it remains aligned with the local plumb line. When the gyroscope wheel inside the gyrocompass device is spun up, the way the gyroscope wheel is suspended causes the gyroscope wheel to gradually align its spinning axis with the Earth's axis. Alignment with the Earth's axis is the only direction for which the gyroscope's spinning axis can be stationary with respect to the Earth and not be required to change direction with respect to inertial space. After being spun up, a gyrocompass can reach the direction of alignment with the Earth's axis in as little as a quarter of an hour.

text: A

text: gyrocompass

text: , employed for navigation of seagoing vessels, finds the geometric north. It does so, not by sensing the Earth's magnetic field, but by using inertial space as its reference. The outer casing of the gyrocompass device is held in such a way that it remains aligned with the local plumb line. When the gyroscope wheel inside the gyrocompass device is spun up, the way the gyroscope wheel is suspended causes the gyroscope wheel to gradually align its spinning axis with the Earth's axis. Alignment with the Earth's axis is the only direction for which the gyroscope's spinning axis can be stationary with respect to the Earth and not be required to change direction with respect to inertial space. After being spun up, a gyrocompass can reach the direction of alignment with the Earth's axis in as little as a quarter of an hour.

text: The north pole of a magnet is defined as the pole that, when the magnet is freely suspended, points towards the Earth's North Magnetic Pole in the Arctic. Since opposite poles (north and south) attract, the North Magnetic Pole is actually the south pole of the Earth's magnetic field. As a practical matter, to tell which pole of a magnet is north and which is south, it is not necessary to use the Earth's magnetic field at all. For example, one method would be to compare it to an electromagnet, whose poles can be identified by the right-hand rule. The magnetic field lines of a magnet are considered by convention to emerge from the magnet's north pole and reenter at the south pole.

text: The north pole of a magnet is defined as the pole that, when the magnet is freely suspended, points towards the Earth's

text: North Magnetic Pole

text: in the Arctic. Since opposite poles (north and south) attract, the North Magnetic Pole is actually the south pole of the Earth's magnetic field. As a practical matter, to tell which

text: pole

text: of a magnet is north and which is south, it is not necessary to use the Earth's magnetic field at all. For example, one method would be to compare it to an

text: electromagnet

text: , whose poles can be identified by the

text: right-hand rule

text: . The magnetic field lines of a magnet are considered by convention to emerge from the magnet's north pole and reenter at the south pole.

text: Originally, the instruments relied on the Earth's magnetic field to provide the restoring force for the compass needle. These were called "tangent" galvanometers and had to be oriented before use. Later instruments of the "astatic" type used opposing magnets to become independent of the Earth's field and would operate in any orientation. The most sensitive form, the Thomson or mirror galvanometer, was patented in 1858 by William Thomson (Lord Kelvin) as an improvement of an earlier design invented in 1826 by Johann Christian Poggendorff. Thomson's design, was able to detect very rapid current changes, by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents. Alternatively, the deflection of the suspended magnets could be observed directly through a microscope.

text: Originally, the instruments relied on the Earth's magnetic field to provide the restoring force for the compass needle. These were called

text: "tangent" galvanometer

text: s and had to be oriented before use. Later instruments of the "

text: astatic

text: " type used opposing magnets to become independent of the Earth's field and would operate in any orientation. The most sensitive form, the Thomson or

text: mirror galvanometer

text: , was patented in 1858 by

text: William Thomson

text: (Lord Kelvin) as an improvement of an earlier design invented in 1826 by

text: Johann Christian Poggendorff

text: . Thomson's design, was able to detect very rapid current changes, by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents. Alternatively, the deflection of the suspended magnets could be observed directly through a microscope.

text: The electric field sensors of sharks are called the ampullae of Lorenzini. They consist of electroreceptor cells connected to the seawater by pores on their snouts and other zones of the head. A problem with the early submarine telegraph cables was the damage caused by sharks who sensed the electric fields produced by these cables. It is possible that sharks may use Earth's magnetic field to navigate the oceans using this sense.

text: The electric field sensors of sharks are called the

text: ampullae of Lorenzini

text: . They consist of electroreceptor cells connected to the seawater by pores on their snouts and other zones of the head. A problem with the early

text: submarine telegraph cable

text: s was the damage caused by sharks who sensed the electric fields produced by these cables. It is possible that sharks may use Earth's

text: magnetic field

text: to navigate the oceans using this sense.

text: The spacecraft was launched from LC-17A at 08:42:00 UTC on October 11, 1958 but it did not reach the Moon as planned due to a programming error in the upper stage causing a slight error in burnout velocity and angle (3.5 deg.). This resulted in a ballistic trajectory with a peak altitude of  around 13:00 local time. The real-time transmission was obtained for about 75% of the flight, but the percentage of data recorded for each experiment was variable. Except for the first hour of flight, the signal-to-noise ratio was good. The spacecraft ended transmission when it reentered the Earth's atmosphere after 43 hours of flight on October 13, 1958 at 03:46 UT over the South Pacific Ocean. A small quantity of useful scientific information was returned, showing the radiation surrounding Earth was in the form of bands and measuring the extent of the bands, mapping the total ionizing flux, making the first observations of hydromagnetic oscillations of the magnetic field, and taking the first measurements of the density of micrometeorites and the Interplanetary Magnetic Field.

text: The spacecraft was launched from

entity_name: Cape Canaveral Air Force Station Space Launch Complex 17

text: at 08:42:00 UTC on October 11, 1958 but it did not reach the Moon as planned due to a programming error in the upper stage causing a slight error in burnout velocity and angle (3.5 deg.). This resulted in a ballistic trajectory with a peak altitude of  around 13:00 local time. The real-time transmission was obtained for about 75% of the flight, but the percentage of data recorded for each experiment was variable. Except for the first hour of flight, the signal-to-noise ratio was good. The spacecraft ended transmission when it reentered the Earth's atmosphere after 43 hours of flight on October 13, 1958 at 03:46 UT over the South

text: Pacific Ocean

text: . A small quantity of useful scientific information was returned, showing the radiation surrounding Earth was in the form of bands and measuring the extent of the bands, mapping the total ionizing flux, making the first observations of hydromagnetic oscillations of the

text: magnetic field

text: , and taking the first measurements of the density of micrometeorites and the

text: Interplanetary Magnetic Field

text: Ferrous metal wire mesh screens are commonly used to protect sea turtle nests from predators' excavating and devouring the eggs and hatchlings.  A new concern is that nestlings' delicate magnetic sense may not develop normally in the presence of the magnetic field interference from                                                    these steel mesh cages.  The effects of the use of steel mesh as a cage material may not be known for many years until assessments can be made of the success rate of the first adult populations that developed within such cages begin attempting landfall for nest-making.  Gravid turtles or their hatchlings may also be affected by the presence of magnetic fields arising from power cables, iron debris,  steel seawalls or other human activities that locally modify earth's magnetic field.

text: He also retained an interest in navigational devices, and with Paul R. Heyl invented the Heyl–Briggs earth inductor compass. The compass used a spinning electric coil subjected to the magnetic field of the Earth to determine the bearing of an airplane in relation to the Earth's magnetic field. For this invention, they received the Magellan Medal of the American Philosophical Society in 1922. This type of compass was used by Admiral Byrd in his flight to the North Pole and by Charles Lindbergh on his 1927 trans-Atlantic flight.

text: He also retained an interest in navigational devices, and with

text: Paul R. Heyl

text: invented the

text: Heyl–Briggs earth inductor compass

text: . The compass used a spinning electric coil subjected to the magnetic field of the Earth to determine the bearing of an airplane in relation to the Earth's

text: magnetic field

text: . For this invention, they received the

text: Magellan Medal

text: of the

text: American Philosophical Society

text: in 1922. This type of compass was used by

text: Admiral Byrd

text: in his flight to the

text: North Pole

text: and by

text: Charles Lindbergh

text: on his 1927 trans-Atlantic flight.

text: At the dawn of the 21st century, numerical modeling of the Earth's magnetic field has not been successfully demonstrated, but appears to be in reach. Initial models are focused on field generation by convection in the planet's fluid outer core. It was possible to show the generation of a strong, Earth-like field when the model assumed a uniform core-surface temperature and exceptionally high viscosities for the core fluid. Computations which incorporated more realistic parameter values yielded magnetic fields that were less Earth-like, but also point the way to model refinements which may ultimately lead to an accurate analytic model.  Slight variations in the core-surface temperature, in the range of a few millikelvins, result in significant increases in convective flow and produce more realistic magnetic fields.

text: The ESSA-9 spacecraft was similar to the TIROS series of satellites, having an 18-sided polygonal shape that measured  in diameter and  high. It weighed . The body of the ESSA-9 was made of aluminum alloy and stainless steel. The shell of the craft was covered with 10,020 solar cells. The solar cells recharged the 63 nickel–cadmium batteries during the time the spacecraft was in sunlight. The ESSA-9 employed the same cartwheel-style stabilization as the TIROS-9 satellite. The satellite used a Magnetic Attitude Spin Coil (MASC) to control its attitude while in orbit. The magnetic field induced by the MASC's current interacted with the earth's magnetic field to provide the torque necessary to maintain a desired spin rate of 9.225 rpm.

text: The ESSA-9 spacecraft was similar to the

entity_name: Television Infrared Observation Satellite

text: TIROS

text: series of satellites, having an 18-sided polygonal shape that measured  in diameter and  high. It weighed . The body of the ESSA-9 was made of

text: aluminum alloy

text: and

text: stainless steel

text: . The shell of the craft was covered with 10,020 solar cells. The solar cells recharged the 63

text: nickel–cadmium batteries

text: during the time the spacecraft was in sunlight. The ESSA-9 employed the same cartwheel-style stabilization as the

text: TIROS

text: -9 satellite. The satellite used a Magnetic Attitude Spin Coil (MASC) to control its attitude while in orbit. The magnetic field induced by the MASC's current interacted with the earth's magnetic field to provide the torque necessary to maintain a desired spin rate of 9.225 rpm.

text: Polarity reversals in the Earth's magnetic field have also been used to determine geologic time. Periodically, the magnetic field of the earth reverses leaving a magnetic signal in volcanic and sedimentary rocks. This signal can be detected and sequences recorded, and in the case of volcanic rocks, tied to radiometric dates.

text: During the second world war these methods of mine protection were standard for all large battle ships. A simple magnetic coil, however, was no longer capable of adequately compensating for the increasingly sophisticated magneto ignition, for the non-uniform magnetic field of a ship and for the variable effects of the Earth's magnetic field in different regions of the world.

text: During the second world war these methods of mine protection were standard for all large battle ships. A simple

text: magnetic coil

text: , however, was no longer capable of adequately compensating for the increasingly sophisticated magneto ignition, for the non-uniform magnetic field of a ship and for the variable effects of the Earth's magnetic field in different regions of the world.

text: Instead, what happens is that rotating a magnet causes subatomic particles in the magnet to acquire a change in velocity. However, in the rotated magnet, the velocities of electrons would vary ahead or behind those of the other particles, due to their lower mass compared to nuclei. There is length contraction of fields propagating from moving charges, and the length contraction of the electric fields E of the electrons would be greater or lesser than the contraction of the E fields of the positive nuclei depending on whether the rotation of the magnet was aligned to, or opposed to, the electron spins which give rise to the magnetism.

text: In the case of an axially-symmetric magnet spinning at constant velocity, the distribution of the magnetic field intensity B of the magnet is constant with time, even after accounting for the relativistic corrections to B, and therefore by the Maxwell–Faraday equation the electric field induced by the rotation of the magnet is curl-free, which is caused purely by length contraction of the electric fields of its constituting subatomic particles. This means that in this particular example with a rotating magnetic disk and a stationary conducting disk, the induced electric field cannot be described by the Maxwell–Faraday equation, which describes the curl of the electric field induced by a changing magnetic flux density.

text: Keeton’s results showed that when the sun was visible, the magnets would not usually prevent the birds from finding their way home, but when the sky was overcast the birds with magnets on their back were much more unsuccessful and slower at finding their way back home than the control birds.  Previous scientists had shown that pigeons were not relying entirely on the sun to navigate home as many scientists had speculated, when they found that many pigeons were able to navigate successfully under completely overcast skies.  This notion led Keeton to question whether the pigeons were using the earth's magnetic field to orient themselves and navigate home successfully.  Keeton’s experiments with magnets showed that there was a combination of processes being used by the pigeons to navigate home, but the use of the earth's magnetic field was very important for pigeon orientation and navigation.

text: The experiment is normally conducted using electrically neutral particles or atoms. This avoids the large deflection to the orbit of a charged particle moving through a magnetic field and allows spin-dependent effects to dominate. For example, observation of the Stern-Gerlach effect with free electrons is infeasible. If the particle is treated as a classical spinning dipole, it will precess in a magnetic field because of the torque that the magnetic field exerts on the dipole (see torque-induced precession). If it moves through a homogeneous magnetic field, the forces exerted on opposite ends of the dipole cancel each other out and the trajectory of the particle is unaffected. However, if the magnetic field is inhomogeneous then the force on one end of the dipole will be slightly greater than the opposing force on the other end, so that there is a net force which deflects the particle's trajectory. If the particles were classical spinning objects, one would expect the distribution of their spin angular momentum vectors to be random and continuous. Each particle would be deflected by a different amount, producing some density distribution on the detector screen. Instead, the particles passing through the Stern–Gerlach apparatus are deflected either up or down by a specific amount. This was a measurement of the quantum observable now known as spin angular momentum, which demonstrated possible outcomes of a measurement where the observable has a discrete set of values or point spectrum. Although some discrete quantum phenomena, such as atomic spectra, were observed much earlier, the Stern–Gerlach experiment allowed scientists to observe separation between discrete quantum states for the first time in the history of science.

text: The experiment is normally conducted using electrically

text: neutral particle

text: s or atoms. This avoids the large deflection to the orbit of a charged particle moving through a magnetic field and allows spin-dependent effects to dominate. For example, observation of the Stern-Gerlach effect with free electrons is infeasible. If the particle is treated as a classical spinning

text: dipole

text: , it will

text: precess

text: in a magnetic field because of the torque that the magnetic field exerts on the dipole (see

text: torque-induced precession

text: ). If it moves through a homogeneous magnetic field, the forces exerted on opposite ends of the dipole cancel each other out and the trajectory of the particle is unaffected. However, if the magnetic field is inhomogeneous then the force on one end of the dipole will be slightly greater than the opposing force on the other end, so that there is a net force which deflects the particle's trajectory. If the particles were classical spinning objects, one would expect the distribution of their spin angular momentum vectors to be

text: random and continuous

text: . Each particle would be deflected by a different amount, producing some density distribution on the detector screen. Instead, the particles passing through the Stern–Gerlach apparatus are deflected either up or down by a specific amount. This was a measurement of the quantum

text: observable

text: now known as

text: spin

text: angular momentum, which demonstrated possible outcomes of a measurement where the observable has a discrete set of values or

text: point spectrum

text: . Although some discrete quantum phenomena, such as

text: atomic spectra

text: , were observed much earlier, the Stern–Gerlach experiment allowed scientists to observe separation between discrete quantum states for the first time in the history of science.

text: The Earth's magnetic field protects the Earth from the deadly solar wind and has long been used for navigation. It originates in the fluid motions of the Earth's outer core (see geodynamo). The magnetic field in the upper atmosphere gives rise to the auroras.

text: The

text: Earth's magnetic field

text: protects the Earth from the deadly

text: solar wind

text: and has long been used for navigation. It originates in the fluid motions of the

text: Earth's outer core

text: (see

text: geodynamo

text: ). The magnetic field in the upper atmosphere gives rise to the

text: auroras

text: A broader disadvantage is the dependence on Earth's magnetic field strength, making this approach unsuitable for deep space missions, and also more suitable for low Earth orbits as opposed to higher ones like the geosynchronous. The dependence on the highly variable intensity of Earth's magnetic field is also problematic because then the attitude control problem becomes highly nonlinear. It is also impossible to control attitude in all three axes even if the full three coils are used, because the torque can be generated only perpendicular to the Earth's magnetic field vector.

text: A broader disadvantage is the dependence on Earth's magnetic field strength, making this approach unsuitable for deep space missions, and also more suitable for

text: low Earth orbit

text: s as opposed to higher ones like the

text: geosynchronous

text: . The dependence on the highly variable intensity of Earth's magnetic field is also problematic because then the attitude control problem becomes highly

text: nonlinear

text: . It is also impossible to control attitude in all three axes even if the full three coils are used, because the torque can be generated only perpendicular to the Earth's magnetic field vector.

text: Any moving conductor, such as sea water, induces an electric field when a magnetic field, such as the earth's is present. The electric fields induced in oceanic currents by the Earth's magnetic field are of the same order of magnitude as the electric fields that sharks and rays are capable of sensing. This could mean that sharks and rays can orient to the electric fields of oceanic currents, and use other sources of electric fields in the ocean for local orientation. Additionally, the electric field they induce in their bodies when swimming in the magnetic field of the Earth may enable them to sense their magnetic heading.

text: Any moving conductor, such as sea water, induces an electric field when a magnetic field, such as the earth's is present. The electric fields induced in oceanic currents by the

text: Earth's magnetic field

text: are of the same order of magnitude as the

text: electric field

text: s that sharks and rays are capable of sensing. This could mean that sharks and rays can orient to the electric fields of oceanic currents, and use other sources of electric fields in the ocean for local orientation. Additionally, the electric field they induce in their bodies when swimming in the magnetic field of the Earth may enable them to sense their magnetic heading.

text: While the North and South magnetic poles are usually located near the geographic poles, they can wander widely over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years, the Earth's field reverses and the North and South Magnetic Poles relatively abruptly switch places. These reversals of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of plate tectonics.

text: While the North and South

text: magnetic pole

text: s are usually located near the geographic poles, they can wander widely over geological time scales, but sufficiently slowly for ordinary

text: compass

text: es to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years,

text: the Earth's field reverses

text: and the North and

text: South Magnetic Pole

text: s relatively abruptly switch places. These reversals of the

text: geomagnetic pole

text: s leave a record in rocks that are of value to

text: paleomagnetists

text: in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors in the process of

text: plate tectonics

text: The radio signal from the antenna (A) is received by a tuner (not shown) and passed through the excitation coil C, the other end of which is connected to ground (E).  The rapidly reversing magnetic field from the coil exceeds the coercivity H and cancels the hysteresis of the iron, causing the magnetization change to suddenly move up the wire to the center, between the magnets, where the field reverses.  This had an effect similar to thrusting a magnet into the coil, causing the magnetic flux through the pickup coil D to change, inducing a current pulse in the pickup coil.  The audio pickup coil is connected to a telephone receiver (earphone) (T) which converts the current pulse to sound.

text: The radio signal from the

text: antenna

text: (A) is received by a tuner (not shown) and passed through the excitation coil C, the other end of which is connected to

text: ground

text: (E).  The rapidly reversing magnetic field from the coil exceeds the coercivity H and cancels the hysteresis of the iron, causing the magnetization change to suddenly move up the wire to the center, between the magnets, where the field reverses.  This had an effect similar to thrusting a magnet into the coil, causing the magnetic flux through the pickup coil D to change, inducing a current pulse in the pickup coil.  The audio pickup coil is connected to a telephone receiver (

text: earphone

text: ) (T) which converts the current pulse to

text: sound

text: The proton magnetometer, also known as the proton precession magnetometer (PPM), uses the principle of  Earth's field nuclear magnetic resonance (EFNMR) to measure very small variations in the Earth's magnetic field, allowing ferrous objects on land and at sea to be detected.

text: The proton magnetometer, also known as the proton precession magnetometer (PPM), uses the principle of

text: Earth's field nuclear magnetic resonance

text: (EFNMR) to measure very small variations in the

text: Earth's magnetic field

text: , allowing

text: ferrous

text: objects on land and at

text: sea

text: to be detected.

text: Some important properties used to compare permanent magnets are: remanence (B), which measures the strength of the magnetic field; coercivity (H), the material's resistance to becoming demagnetized; energy product (BH), the density of magnetic energy; and Curie temperature (T), the temperature at which the material loses its magnetism.  Rare earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types.  The table below compares the magnetic performance of the two types of rare earth magnet, neodymium (NdFeB) and samarium-cobalt (SmCo), with other types of permanent magnets.

text: Some important properties used to compare permanent magnets are:

text: remanence

text: (B), which measures the strength of the magnetic field;

text: coercivity

text: (H), the material's resistance to becoming demagnetized; energy product (BH), the density of magnetic energy; and

text: Curie temperature

text: (T), the temperature at which the material loses its magnetism.  Rare earth magnets have higher remanence, much higher coercivity and energy product, but (for neodymium) lower Curie temperature than other types.  The table below compares the magnetic performance of the two types of rare earth magnet, neodymium (NdFeB) and samarium-cobalt (SmCo), with other types of permanent magnets.

text: Iron oxide nanoparticles are used in cancer magnetic nanotherapy that is based on the magneto-spin effects in free radical reactions and semiconductor material ability to generate oxygen radicals, furthermore, control oxidative stress in biological media under inhomogeneous electromagnetic radiation. The magnetic nanotherapy is remotely controlled by external electromagnetic field ROS (reactive oxygen species)-mediated local toxicity in the tumor during chemotherapy with antitumor magnetic complex and lesser side effects in normal tissues. Magnetic complexes that consist of iron oxide nanoparticles loaded with antitumor drug have additional advantages over conventional antitumor drugs due to their ability to be remotely controlled while targeting with a constant magnetic field and further strengthening of their antitumor activity by moderate inductive hyperthermia (below 40 °C).The combined influence of inhomogeneous constant magnetic and electromagnetic fields during nanotherapy has initiated splitting of electron energy levels in magnetic complex and unpaired electron transfer from iron oxide nanoparticles to anticancer drug and tumor cells. In particular,  anthracycline antitumor antibiotic doxorubicin, the native state of which is diamagnetic, acquires the magnetic properties of paramagnetic substances. Electromagnetic radiation at the hyperfine splitting frequency can increase time radical pairs are in the triplet state and hence the probability of dissociation and so the concentration of free radicals. The reactivity of magnetic particles depends on their spin state. The experimental data was received about correlation between the frequency of electromagnetic field radiation with magnetic properties and quantity paramagnetic centres of complex. It is possible to control the kinetics of free radical reactions by external magnetic fields and modulate the level of oxidative stress (local toxicity) in malignant tumor. Cancer cells are then particularly vulnerable to an oxidative assault and induction of high levels of oxidative stress locally in tumor tissue, that has the potential to destroy or arrest the growth of cancer cells and can be thought as therapeutic strategy against cancer. Multifunctional magnetic complexes can combine cancer magnetic nanotherapy, tumor targeting and medical imaging functionalities in theranostics approach for personalized cancer medicine.

text: Iron oxide nanoparticles are used in cancer magnetic nanotherapy that is based on the magneto-spin effects in

text: free radical reactions

text: and semiconductor material ability to generate

text: oxygen radicals

text: , furthermore, control

text: oxidative stress

text: in biological media under inhomogeneous

text: electromagnetic radiation

text: . The magnetic nanotherapy is remotely controlled by external

text: electromagnetic field

text: ROS (reactive oxygen species)

text: -mediated local

text: toxicity

text: in the

text: tumor

text: during

text: chemotherapy

text: with antitumor magnetic complex and lesser side effects in normal tissues. Magnetic complexes that consist of iron oxide nanoparticles loaded with

text: antitumor drug

text: have additional advantages over conventional

text: antitumor drugs

text: due to their ability to be remotely controlled while

text: targeting

text: with a

text: constant magnetic field

text: and further strengthening of their antitumor activity by moderate

text: inductive hyperthermia

text: (below 40 °C).The combined influence of inhomogeneous

text: constant magnetic

text: and

text: electromagnetic field

text: s during nanotherapy has initiated

text: splitting of electron energy levels

text: in magnetic complex and unpaired

text: electron transfer

text: from iron oxide nanoparticles to

text: anticancer drug

text: and

text: tumor cells

text: . In particular,  anthracycline antitumor antibiotic doxorubicin, the native state of which is

text: diamagnetic

text: , acquires the magnetic properties of

text: paramagnetic

text: substances.

text: Electromagnetic radiation

text: at the

text: hyperfine splitting

text: frequency can increase time radical pairs are in the

text: triplet state

text: and hence the probability of

text: dissociation

text: and so the concentration of

text: free radicals

text: The reactivity

text: of magnetic particles depends on their

text: spin state

text: . The experimental data was received about correlation between the frequency of electromagnetic field radiation with magnetic properties and quantity paramagnetic centres of complex. It is possible to control the

text: kinetics

text: of

text: free radical reactions

text: by external

text: magnetic field

text: s and modulate the level of

text: oxidative stress

text: (local toxicity) in

text: malignant tumor

text: Cancer cell

text: s are then particularly vulnerable to an oxidative assault and induction of high levels of

text: oxidative stress

text: locally in tumor tissue, that has the potential to destroy or arrest the growth of cancer cells and can be thought as therapeutic strategy against cancer. Multifunctional magnetic complexes can combine cancer magnetic nanotherapy, tumor

text: targeting

text: and

text: medical imaging

text: functionalities in theranostics approach for personalized cancer medicine.

text: An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field.  The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.

text: An

text: electromagnet

text: is a type of

text: magnet

text: in which the

text: magnetic field

text: is produced by an

text: electric current

text: . The magnetic field disappears when the current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field.  The wire turns are often wound around a

text: magnetic core

text: made from a

text: ferromagnetic

text: or

text: ferrimagnetic

text: material such as

text: iron

text: ; the magnetic core concentrates the

text: magnetic flux

text: and makes a more powerful magnet.

text: Mayer described two new types of torpedoes in service with the German navy. The first was a type of acoustic torpedo designed to be used from distances of . It was intended to be steered close to a convoy using a long wave radio receiver, when two acoustic receivers in the head of the torpedo would take over when it came within a few hundred metres of a ship. The second type of torpedo (mentioned as the same type that was used to sink HMS Royal Oak in 1939), was described as having a magnetic fuze designed to detect the deviations in the Earth's magnetic field caused by a ship's metal hull and explode beneath its keel. Mayer described the principle of the fuze and suggested that it could be defended against by generating a suitable magnetic field.

text: Mayer described two new types of torpedoes in service with the German navy. The first was a type of

text: acoustic torpedo

text: designed to be used from distances of . It was intended to be steered close to a convoy using a long wave radio receiver, when two acoustic receivers in the head of the torpedo would take over when it came within a few hundred metres of a ship. The second type of torpedo (mentioned as the same type that was used to sink

text: HMS Royal Oak

text: in 1939), was described as having a

text: magnetic fuze

text: designed to detect the deviations in the

text: Earth's magnetic field

text: caused by a ship's metal hull and explode beneath its keel. Mayer described the principle of the fuze and suggested that it could be defended against by generating a suitable magnetic field.

text: Homing pigeons use magnetic field information with other navigational cues. Pioneering researcher William Keeton showed that time-shifted homing pigeons could not orient themselves correctly on a clear sunny day, but could do so on an overcast day, suggesting that the birds prefer to rely on the direction of the sun, but switch to using a magnetic field cue when the sun is not visible. This was confirmed by experiments with magnets: the pigeons could not orient correctly on an overcast day when the magnetic field was disrupted.

text: Magnetic multilayers: Nano-wires consisting of alternating magnetic/nonmagnetic layers act as magnetic sensors. As an example, cobalt/copper nanowires are obtained from an electrolyte containing both metals. At low voltage, pure copper is deposited while cobalt resists electro-deposition. At high voltage, both metals are deposited as an alloy. If the electrolyte contains predominantly cobalt, a magnetic cobalt-copper alloy is deposited with a high fraction of cobalt. The electrical conductivity of the multilayer wire depends on the applied external magnetic field. The magnetic order of the cobalt layers increases with the applied field. Without magnetic field, neighboring magnetic layers prefer the anti-parallel order. With magnetic field, the magnetic layers prefer the orientation parallel with the magnetic field. The parallel orientation corresponds to a reduced electrical resistance. The effect is used in reading heads of magnetic storage media (the "GMR effect").

text: Magnetic multilayers: Nano-wires consisting of alternating magnetic/nonmagnetic layers act as magnetic sensors. As an example, cobalt/copper nanowires are obtained from an

text: electrolyte

text: containing both metals. At low voltage, pure copper is deposited while cobalt resists electro-deposition. At high voltage, both metals are deposited as an alloy. If the

text: electrolyte

text: contains predominantly cobalt, a magnetic cobalt-copper alloy is deposited with a high fraction of cobalt. The electrical conductivity of the multilayer wire depends on the applied external magnetic field. The magnetic order of the cobalt layers increases with the applied field. Without magnetic field, neighboring magnetic layers prefer the anti-parallel order. With magnetic field, the magnetic layers prefer the orientation parallel with the magnetic field. The parallel orientation corresponds to a reduced electrical resistance. The effect is used in reading heads of magnetic storage media (the "GMR effect").

text: Neutron stars have strong magnetic fields. The magnetic field strength on the surface of neutron stars have been estimated at least to have the range of 10 to 10 gauss (10 to 10 tesla). In comparison, the magnitude at Earth's surface ranges from 25 to 65 microteslas (0.25 to 0.65 gauss), making the field at least 10 times as strong as that of Earth. Variations in magnetic field strengths are most likely the main factor that allows different types of neutron stars to be distinguished by their spectra, and explains the periodicity of pulsars. The neutron stars known as magnetars have the strongest magnetic fields, in the range of 10 to 10 tesla, and have become the widely accepted hypothesis for neutron star types soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs).

text: Neutron stars have strong magnetic fields. The magnetic field strength on the surface of neutron stars have been estimated at least to have the range of 10 to 10

text: gauss

text: (10 to 10

text: tesla

text: ). In comparison, the magnitude at Earth's surface ranges from 25 to 65

text: microteslas

text: (0.25 to 0.65

text: gauss

text: ), making the field at least 10 times as strong as that of Earth. Variations in magnetic field strengths are most likely the main factor that allows different types of neutron stars to be distinguished by their spectra, and explains the periodicity of pulsars. The neutron stars known as

text: magnetar

text: s have the strongest magnetic fields, in the range of 10 to 10

text: tesla

text: , and have become the widely accepted hypothesis for neutron star types

text: soft gamma repeater

text: s (SGRs) and

text: anomalous X-ray pulsar

text: s (AXPs).

text: Earth's magnetic field results from its flowing liquid metallic core, but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles. Magnesium oxide, which is rocky on Earth, can be a liquid metal at the pressures and temperatures found in super-Earths and could generate a magnetic field in the mantles of super-Earths. That said, super-Earth magnetic fields are yet to be detected observationally.

text: For passive attitude control, Pegaso uses a series of magnets and inertial-magnetic dampers for single-axis alignment along Earth's magnetic field.

text: For passive

text: attitude control

text: , Pegaso uses a series of magnets and inertial-magnetic dampers for single-axis alignment along

text: Earth's magnetic field

text: Compasses are used to determine the direction of true North. However, the compass reading must be corrected for two effects. The first is magnetic declination or variation, the angular difference between magnetic North (the local direction of the Earth's magnetic field) and true North. The second is magnetic deviation, the angular difference between magnetic North and the compass needle due to nearby sources of interference such as magnetically permeable bodies, or other magnetic fields within the field of influence.

text: Compasses are used to determine the direction of

text: true North

text: . However, the compass reading must be corrected for two effects. The first is

text: magnetic declination

text: or variation, the angular difference between magnetic North (the local direction of the

text: Earth's magnetic field

text: ) and true North. The second is magnetic deviation, the angular difference between magnetic North and the compass needle due to nearby sources of interference such as magnetically permeable bodies, or other magnetic fields within the field of influence.

text: The mid-ocean ridge systems form new oceanic crust. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of the field in the oceanic crust record preserve a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at irregular intervals throughout its history, the pattern of geomagnetic reversals in the ocean crust can be used as an indicator of age. Likewise, the pattern of reversals together with age measurements of the crust is used to help establish the history of the Earth's magnetic field.

text: The mid-ocean ridge systems form new oceanic crust. As crystallized basalt extruded at a ridge axis cools below

text: Curie point

text: s of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of the field in the oceanic crust record preserve a record of directions of the

text: Earth's magnetic field

text: with time. Because the field has reversed directions at irregular intervals throughout its history, the pattern of

text: geomagnetic reversals

text: in the ocean crust can be used as an indicator of age. Likewise, the pattern of reversals together with age measurements of the crust is used to help establish the history of the Earth's magnetic field.

text: The effect is caused by the non-concentricity of the Earth and its magnetic dipole. The SAA is the near-Earth region where the Earth's magnetic field is weakest relative to an idealized Earth-centered dipole field.

text: The effect is caused by the

text: non-concentricity

text: of the Earth and its magnetic

text: dipole

text: . The SAA is the near-Earth region where the

text: Earth's magnetic field

text: is weakest relative to an idealized Earth-centered dipole field.

text: A very common source of magnetic field shown in nature is a dipole, with a "South pole" and a "North pole", terms dating back to the use of magnets as compasses, interacting with the Earth's magnetic field to indicate North and South on the globe. Since opposite ends of magnets are attracted, the north pole of a magnet is attracted to the south pole of another magnet.  The Earth's North Magnetic Pole (currently in the Arctic Ocean, north of Canada) is physically a south pole, as it attracts the north pole of a compass.A magnetic field contains energy, and physical systems move toward configurations with lower energy. When diamagnetic material is placed in a magnetic field, a magnetic dipole tends to align itself in opposed polarity to that field, thereby lowering the net field strength. When ferromagnetic material is placed within a magnetic field, the magnetic dipoles align to the applied field, thus expanding the domain walls of the magnetic domains.

text: A very common source of magnetic field shown in nature is a

text: dipole

text: , with a "

text: South pole

text: " and a "

text: North pole

text: ", terms dating back to the use of magnets as compasses, interacting with the

text: Earth's magnetic field

text: to indicate North and South on the

text: globe

text: . Since opposite ends of magnets are attracted, the north pole of a magnet is attracted to the south pole of another magnet.  The Earth's

text: North Magnetic Pole

text: (currently in the Arctic Ocean, north of Canada) is physically a south pole, as it attracts the north pole of a compass.A magnetic field contains

text: energy

text: , and physical systems move toward configurations with lower energy. When diamagnetic material is placed in a magnetic field, a magnetic dipole tends to align itself in opposed polarity to that field, thereby lowering the net field strength. When ferromagnetic material is placed within a magnetic field, the magnetic dipoles align to the applied field, thus expanding the domain walls of the magnetic domains.

text: The site holds various facilities. The main Land Magnetic Range is a secure and magnetically stable environment, used to measure the magnetic fields found in Mine Counter Measure Vessel equipment. The range uses inbuilt coil systems which enable the Earth's magnetic field to be reduced to zero, simulate anywhere on the planet, or provide only the vertical or horizontal portion of the Earth field to pass through the item under test, which an equivalent Sea Range cannot do. The Compass Test Centre inspects and tests magnetic compasses, whilst also delivering them to RAF stations across the UK. The Compass Base Calibration Surveys is a designated area of survey and certification, used for accurate swinging of Aircraft Navigation Equipment for both military and civilian airfields.

text: Anti-magnetic seal (from ) or anti-magnetic sticker, indicator of the  magnetic field is a device that serves to indicate the influence of magnetic fields on the protected object and helps to reduce theft of energy (electricity, water, gas, heat, fuel).

text: Anti-magnetic

text: seal

text: (from ) or anti-magnetic sticker, indicator of the

text: magnetic field

text: is a device that serves to indicate the influence of magnetic fields on the protected object and helps to reduce theft of energy (electricity, water, gas, heat, fuel).

text: The Moon has an external magnetic field of about 1–100 nanoteslas, less than one-hundredth that of Earth. It does not currently have a global dipolar magnetic field and only has crustal magnetization, probably acquired early in lunar history when a dynamo was still operating. Alternatively, some of the remnant magnetization may be from transient magnetic fields generated during large impact events through the expansion of an impact-generated plasma cloud in the presence of an ambient magnetic field. This is supported by the apparent location of the largest crustal magnetizations near the antipodes of the giant impact basins.

text: The Moon has an external

text: magnetic field

text: of about 1–100

text: nanoteslas

text: , less than one-hundredth

text: that of Earth

text: . It does not currently have a global

text: dipolar

text: magnetic field and only has crustal magnetization, probably acquired early in lunar history when a dynamo was still operating. Alternatively, some of the remnant magnetization may be from transient magnetic fields generated during large impact events through the expansion of an impact-generated plasma cloud in the presence of an ambient magnetic field. This is supported by the apparent location of the largest crustal magnetizations near the

text: antipodes

text: of the giant impact basins.

text: Neodymium magnets, invented in the 1980s, are the strongest and most affordable type of rare-earth magnet.  They are made of an alloy of neodymium, iron, and boron (NdFeB), sometimes abbreviated as NIB.   Neodymium magnets are used in numerous applications requiring strong, compact permanent magnets, such as electric motors for cordless tools, hard disk drives, magnetic holddowns, and jewelry clasps. They have the highest magnetic field strength and have a higher coercivity (which makes them magnetically stable), but they have a lower Curie temperature, m and are more vulnerable to oxidation than samarium–cobalt magnets.  Corrosion can cause unprotected magnets to spall off a surface layer, or to crumble into a powder.  Use of protective surface treatments such as gold, nickel, zinc, and tin plating and epoxy resin coating can provide corrosion protection.

text: Neodymium

text: magnets, invented in the 1980s, are the strongest and most affordable type of rare-earth

text: magnet

text: .  They are made of an alloy of

text: neodymium

text: iron

text: , and

text: boron

text: Nd

text: Fe

text: B

text: ), sometimes abbreviated as NIB.   Neodymium magnets are used in numerous applications requiring strong, compact permanent magnets, such as electric motors for

text: cordless tools

text: hard disk drive

text: s, magnetic holddowns, and jewelry clasps. They have the highest magnetic field strength and have a higher

text: coercivity

text: (which makes them magnetically stable), but they have a lower

text: Curie temperature

text: , m and are more vulnerable to

text: oxidation

text: than samarium–cobalt magnets.

text: Corrosion

text: can cause unprotected magnets to

text: spall

text: off a surface layer, or to crumble into a powder.  Use of protective surface treatments such as

text: gold

text: nickel

text: zinc

text: , and

text: tin

text: plating and epoxy resin coating can provide corrosion protection.

text: In the vortex state, a phenomenon known as flux pinning, where a superconductor is pinned in space above a magnet, becomes possible. This is not possible with type-I superconductors, since they cannot be penetrated by magnetic fields. Since the superconductor is pinned above the magnet away from any surfaces, there is the potential for a frictionless joint. The worth of flux pinning is seen through many implementations such as lifts, frictionless joints, and transportation. The thinner the superconducting layer, the stronger the pinning that occurs when exposed to magnetic fields.

text: In the vortex state, a phenomenon known as

text: flux pinning

text: , where a superconductor is pinned in space above a magnet, becomes possible. This is not possible with

text: type-I superconductor

text: s, since they cannot be penetrated by magnetic fields. Since the superconductor is pinned above the magnet away from any surfaces, there is the potential for a frictionless joint. The worth of flux pinning is seen through many implementations such as lifts, frictionless joints, and transportation. The thinner the superconducting layer, the stronger the pinning that occurs when exposed to magnetic fields.

text: Being magnetic devices, audio transformers are susceptible to external magnetic fields such as those generated by AC current-carrying conductors. "Hum" is a term commonly used to describe unwanted signals originating from the "mains" power supply (typically 50 or 60 Hz). Audio transformers used for low-level signals, such as those from microphones, often include magnetic shielding to protect against extraneous magnetically coupled signals.

text: Being magnetic devices, audio transformers are susceptible to external magnetic fields such as those generated by AC current-carrying conductors. "

text: Hum

text: " is a term commonly used to describe unwanted signals originating from the "

text: mains

text: " power supply (typically 50 or 60 Hz). Audio transformers used for low-level signals, such as those from microphones, often include

text: magnetic shielding

text: to protect against extraneous magnetically coupled signals.

text: A magnetic compass aboard an aircraft displays the current magnetic heading of the aircraft, i.e., the aircraft's directional orientation relative to the Earth's geomagnetic field, which has a roughly north-south orientation.  The compass can be used in turns to verify  the aircraft is travelling in the desired direction at the conclusion of a turn. The nature of the instrument and the alignment of the magnetic pole of the earth cause the magnetic compass to have several significant limitations when used for navigation. A pilot aware of those limitations can use the compass effectively for navigation. The compass continues to operate despite failures in the electrical, vacuum or pitot static systems.

text: A magnetic

text: compass

text: aboard an aircraft displays the current magnetic heading of the aircraft, i.e., the aircraft's directional orientation relative to the Earth's

text: geomagnetic field

text: , which has a roughly north-south orientation.  The compass can be used in turns to verify  the aircraft is travelling in the desired direction at the conclusion of a turn. The nature of the instrument and the alignment of the magnetic pole of the earth cause the magnetic compass to have several significant limitations when used for navigation. A pilot aware of those limitations can use the compass effectively for navigation. The compass continues to operate despite failures in the electrical, vacuum or pitot static systems.

text: Magnetic compasses are influenced by any fields other than Earth's. Local environments may contain magnetic mineral deposits and artificial sources such as MRIs, large iron or steel bodies, electrical engines or strong permanent magnets. Any electrically conductive body produces its own magnetic field when it is carrying an electric current. Magnetic compasses are prone to errors in the neighborhood of such bodies. Some compasses include magnets which can be adjusted to compensate for external magnetic fields, making the compass more reliable and accurate.

text: Magnetic compasses are influenced by any fields other than Earth's. Local environments may contain magnetic mineral deposits and artificial sources such as

text: MRI

text: s, large iron or steel bodies, electrical engines or strong permanent magnets. Any electrically conductive body produces its own magnetic field when it is carrying an electric current. Magnetic compasses are prone to errors in the neighborhood of such bodies. Some compasses include magnets which can be adjusted to compensate for external magnetic fields, making the compass more reliable and accurate.

text: Early European navigators believed that compass needles were attracted to a "magnetic island" somewhere in the far north (see Rupes Nigra), or to the Pole Star. The idea that the Earth itself acts as a giant magnet was first proposed in 1600 by the English physician and natural philosopher William Gilbert. He was also the first to define the North Magnetic Pole as the point where the Earth's magnetic field points vertically downwards. This is the definition used nowadays, though it would be a few hundred years before the nature of the Earth's magnetic field was understood properly.

text: Early European navigators believed that compass needles were attracted to a "magnetic island" somewhere in the far north (see

text: Rupes Nigra

text: ), or to the

text: Pole Star

text: . The idea that the Earth itself acts as a giant magnet was first proposed in 1600 by the English physician and natural philosopher

text: William Gilbert

text: . He was also the first to define the North Magnetic Pole as the point where the Earth's magnetic field points vertically downwards. This is the definition used nowadays, though it would be a few hundred years before the nature of the Earth's magnetic field was understood properly.

text: The other question is how lodestones get magnetized.  The Earth's magnetic field at 0.5 gauss is too weak to magnetize a lodestone by itself.  The leading theory is that lodestones are magnetized by the strong magnetic fields surrounding lightning bolts. This is supported by the observation that they are mostly found near the surface of the Earth, rather than buried at great depth.

text: The other question is how lodestones get

text: magnetize

text: d.  The

text: Earth's magnetic field

text: at 0.5

text: gauss

text: is too weak to magnetize a lodestone by itself.  The leading theory is that lodestones are magnetized by the strong magnetic fields surrounding

text: lightning

text: bolts. This is supported by the observation that they are mostly found near the surface of the Earth, rather than buried at great depth.

text: In everyday life, magnetic fields are most often encountered as a force created by permanent magnets, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets. Magnetic fields are widely used throughout modern technology, particularly in electrical engineering and electromechanics. The Earth produces its own magnetic field, which is important in navigation, and it shields the Earth's atmosphere from solar wind. Rotating magnetic fields are used in both electric motors and generators. Magnetic forces give information about the charge carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits.

text: In everyday life, magnetic fields are most often encountered as a

text: force

text: created by

text: permanent magnet

text: s, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets. Magnetic fields are widely used throughout modern technology, particularly in

text: electrical engineering

text: and

text: electromechanics

text: . The Earth produces

text: its own magnetic field

text: , which is important in navigation, and it shields the Earth's atmosphere from

text: solar wind

text: . Rotating magnetic fields are used in both

text: electric motor

text: s and

text: generators

text: . Magnetic forces give information about the charge carriers in a material through the

text: Hall effect

text: . The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of

text: magnetic circuit

text: s.

text: Magnetometers detect minute deviations in the Earth's magnetic field caused by iron artifacts, kilns, some types of stone structures, and even ditches and middens in archaeological geophysics. Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped. Basalt — the iron-rich, volcanic rock making up the ocean floor — contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.

text: Magnetometer

text: s detect minute deviations in the Earth's magnetic field caused by iron

text: artifacts

text: , kilns, some types of stone structures, and even ditches and

text: midden

text: s in

text: archaeological geophysics

text: . Using magnetic instruments adapted from airborne

text: magnetic anomaly detector

text: s developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped.

text: Basalt

text: — the iron-rich, volcanic rock making up the ocean floor — contains a strongly magnetic mineral (

text: magnetite

text: ) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.

text: Magnetic fields are vector quantities characterized by both strength and direction. The strength of a magnetic field is measured in units of tesla in the SI units, and in gauss in the cgs system of units. 10,000 gauss are equal to one tesla. Measurements of the Earth's magnetic field are often quoted in units of nanotesla (nT), also called a gamma. The Earth's magnetic field can vary from 20,000 to 80,000 nT depending on location, fluctuations in the Earth's magnetic field are on the order of 100 nT, and magnetic field variations due to magnetic anomalies can be in the picotesla (pT) range. Gaussmeters and teslameters are magnetometers that measure in units of gauss or tesla, respectively. In some contexts, magnetometer is the term used for an instrument that measures fields of less than 1 millitesla (mT) and gaussmeter is used for those measuring greater than 1 mT.

text: Magnetic field

text: s are

text: vector

text: quantities characterized by both strength and direction. The strength of a magnetic field is measured in units of

text: tesla

text: in the

text: SI unit

text: s, and in

text: gauss

text: in the

text: cgs system

text: of units. 10,000 gauss are equal to one tesla. Measurements of the Earth's magnetic field are often quoted in units of nanotesla (nT), also called a gamma. The Earth's magnetic field can vary from 20,000 to 80,000 nT depending on location, fluctuations in the Earth's magnetic field are on the order of 100 nT, and magnetic field variations due to

text: magnetic anomalies

text: can be in the picotesla (pT) range. Gaussmeters and teslameters are magnetometers that measure in units of gauss or tesla, respectively. In some contexts, magnetometer is the term used for an instrument that measures fields of less than 1 millitesla (mT) and gaussmeter is used for those measuring greater than 1 mT.

text: The Earth has a magnetic field which is not quite in line with the geographic directions. The difference between the magnetic and true directions is known as Variation. It differs from place to place and changes with time. Large scale charts and maps will usually include a compass rose showing variation.

text: The Earth has a magnetic field which is not quite in line with the geographic directions. The difference between the magnetic and true directions is known as

text: Variation

text: . It differs from place to place and changes with time. Large scale charts and maps will usually include a

text: compass rose

text: showing variation.

text: The magnetization or magnetic polarization of a magnetic material is the vector field that expresses the density of permanent or induced magnetic moments. The magnetic moments can originate from microscopic electric currents caused by the motion of electrons in individual atoms, or the spin of the electrons or the nuclei. Net magnetization results from the response of a material to an external magnetic field, together with any unbalanced magnetic moment that may be present even in the absence of the external magnetic field; for example, in sufficiently cold iron. We call the latter spontaneous magnetization. Other materials that share this property with iron, like Nickel and magnetite, are called ferromagnets. The threshold temperature below which a material is ferromagnetic is called the Curie temperature and varies between materials.

text: The

text: magnetization

text: or

text: magnetic polarization

text: of a magnetic material is the

text: vector field

text: that expresses the

text: density

text: of permanent or induced

text: magnetic moments

text: . The magnetic moments can originate from microscopic

text: electric currents

text: caused by the motion of

text: electrons

text: in individual

text: atoms

text: , or the

text: spin

text: of the electrons or the nuclei. Net magnetization results from the response of a material to an external

text: magnetic field

text: , together with any unbalanced

text: magnetic moment

text: that may be present even in the absence of the external

text: magnetic field

text: ; for example, in sufficiently cold

text: iron

text: . We call the latter

text: spontaneous magnetization

text: . Other materials that share this property with iron, like

text: Nickel

text: and

text: magnetite

text: , are called

text: ferromagnets

text: . The threshold temperature below which a material is ferromagnetic is called the

text: Curie temperature

text: and varies between materials.

text: Magnetoception (or magnetoreception) is the ability to detect the direction one is facing based on the Earth's magnetic field. Directional awareness is most commonly observed in birds, which rely on their magnetic sense to navigate during migration. It has also been observed in insects such as bees. Cattle make use of magnetoception to align themselves in a north-south direction. Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field.

text: Magnetoception

text: (or magnetoreception) is the ability to detect the direction one is facing based on the Earth's

text: magnetic field

text: . Directional awareness is most commonly observed in

text: bird

text: s, which rely on their magnetic sense to navigate during migration. It has also been observed in insects such as

text: bee

text: s. Cattle make use of magnetoception to align themselves in a north-south direction.

text: Magnetotactic bacteria

text: build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field.

text: A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The term is used for two distinct but closely related fields denoted by the symbols  and , where  is measured in units of amperes per meter (symbol: A·m or A/m) in the SI.  is measured in teslas (symbol: T; note that although the symbol is capital T, "tesla" is written in lower case in the SI system) and newtons per meter per ampere (symbol: N·m·A or N/(m·A)) in the SI.  is most commonly defined in terms of the Lorentz force it exerts on moving electric charges.

text: A magnetic field is the magnetic effect of

text: electric current

text: s and

text: magnetic materials

text: . The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a

text: vector field

text: . The term is used for two distinct but closely related fields denoted by the symbols  and , where  is measured in units of

text: ampere

text: s per

text: meter

text: (symbol: A·m or A/m) in the

text: SI

text: .  is measured in

text: tesla

text: s (symbol: T; note that although the symbol is capital T, "tesla" is written in lower case in the SI system) and

text: newton

text: s per

text: meter

text: per

text: ampere

text: (symbol: N·m·A or N/(m·A)) in the

text: SI

text: .  is most commonly defined in terms of the

text: Lorentz force

text: it exerts on moving electric charges.

text: When a sample is placed in a constant magnetic field and stimulated (perturbed) by a time-varying (e.g., pulsed or alternating) magnetic field, NMR active nuclei resonate at characteristic frequencies. Examples of such NMR active nuclei are the isotopes carbon-13 and hydrogen-1 (hydrogen-1 often being referred as Protium). The resonant frequency of each isotope is directly proportional to the strength of the applied magnetic field, and the magnetogyric or gyromagnetic ratio of that isotope. The signal strength is proportional both to the stimulating magnetic field and the number of nuclei of that isotope in the sample. Thus in the 21 tesla magnetic field that may be found in high resolution laboratory NMR spectrometers, protons resonate at 900 MHz. However, in the Earth's magnetic field the same nuclei resonate at audio frequencies of around 2 kHz and generate very weak signals.

text: When a sample is placed in a constant magnetic field and stimulated (perturbed) by a time-varying (e.g., pulsed or alternating) magnetic field, NMR active nuclei resonate at characteristic frequencies. Examples of such NMR active nuclei are the

text: isotope

text: s

text: and

text: (hydrogen-1 often being referred as

text: Protium

text: ). The resonant frequency of each isotope is directly proportional to the strength of the applied magnetic field, and the

text: magnetogyric or gyromagnetic ratio

text: of that isotope. The signal strength is proportional both to the stimulating magnetic field and the number of nuclei of that isotope in the sample. Thus in the 21

text: tesla

text: magnetic field that may be found in high resolution laboratory

text: NMR spectrometers

text: , protons resonate at 900 MHz. However, in the Earth's magnetic field the same nuclei resonate at audio frequencies of around 2 kHz and generate very weak signals.

text: There are certain circumstances when magnetic compasses and gyrocompasses are unreliable. The most obvious is in polar regions, where the force exerted on the needle of a magnetic compass is nearly vertical and gyrocompasses become unstable due to the rotation of the Earth. Magnetic compasses are also susceptible to disruption from magnetic fields other than the Earth's, such as those produced by the hulls of some metal vehicles or craft. Before the advent of electronic navigational aids such as GPS the most reliable way to ascertain north in such circumstances was through the use of an astrocompass.

text: There are certain circumstances when magnetic

text: compass

text: es and

text: gyrocompass

text: es are unreliable. The most obvious is in

text: polar regions

text: , where the force exerted on the needle of a magnetic compass is nearly vertical and gyrocompasses become unstable due to the rotation of the

text: Earth

text: . Magnetic compasses are also susceptible to disruption from magnetic fields other than the Earth's, such as those produced by the hulls of some metal vehicles or craft. Before the advent of electronic navigational aids such as

text: GPS

text: the most reliable way to ascertain north in such circumstances was through the use of an astrocompass.

text: Venus is similar to Earth in size and density, and so probably also in bulk composition, but it does not have a significant magnetic field. Earth's magnetic field is produced by what is known as the core dynamo, consisting of an electrically conducting liquid, the nickel-iron outer core that rotates and is convecting. Venus is expected to have an electrically conductive core of similar composition, and although its rotation period is very long (243.7 Earth days), simulations show that this is adequate to produce a dynamo. This implies that Venus lacks convection in its outer core. Convection occurs when there is a large difference in temperature between the inner and outer part of the core, but since Venus has no plate tectonics to let off heat from the mantle, it is possible that outer core convection is being suppressed by a warm mantle. It's also possible that Venus may lack a solid inner core for the same reason, if the core is either too hot or is not under enough pressure to allow molten nickel-iron to freeze there.

text: Venus is similar to Earth in size and density, and so probably also in bulk composition, but it does not have a significant

text: magnetic field

text: . Earth's magnetic field is produced by what is known as the

text: core dynamo

text: , consisting of an electrically conducting liquid, the nickel-iron outer core that rotates and is

text: convecting

text: . Venus is expected to have an electrically conductive core of similar composition, and although its rotation period is very long (243.7 Earth days), simulations show that this is adequate to produce a dynamo. This implies that Venus lacks convection in its outer core. Convection occurs when there is a large difference in temperature between the inner and outer part of the core, but since Venus has no plate tectonics to let off heat from the mantle, it is possible that outer core convection is being suppressed by a warm mantle. It's also possible that Venus may lack a solid inner core for the same reason, if the core is either too hot or is not under enough pressure to allow molten nickel-iron to freeze there.

text: The device works by hysteresis of the magnetization in the iron wires.  The permanent magnets are arranged to create two opposite magnetic fields each directed toward (or away) from the center of the coils in opposite directions along the wire.  This functions to magnetize the iron band along its axis, first in one direction as it approaches the center of the coils, then reverse its magnetism to the opposite direction as it leaves from the other side of the coil.  Due to the hysteresis (coercivity) of the iron, a certain threshold magnetic field (the coercive field, H) is required to reverse the magnetization, so the magnetization in the moving wires does not reverse in the center of the device where the field reverses, but some way toward the departing side of the wires.   Although the wire itself is moving through the coil, in the absence of a radio signal the location where the magnetization "flips" is stationary with respect to the coil, so there is no flux change and no voltage is induced in the pickup coil.

text: The device works by

text: hysteresis

text: of the magnetization in the iron wires.  The

text: permanent magnet

text: s are arranged to create two opposite

text: magnetic field

text: s each directed toward (or away) from the center of the coils in opposite directions along the wire.  This functions to magnetize the iron band along its axis, first in one direction as it approaches the center of the coils, then reverse its magnetism to the opposite direction as it leaves from the other side of the coil.  Due to the hysteresis (

text: coercivity

text: ) of the iron, a certain threshold magnetic field (the

text: coercive field

text: , H) is required to reverse the magnetization, so the magnetization in the moving wires does not reverse in the center of the device where the field reverses, but some way toward the departing side of the wires.   Although the wire itself is moving through the coil, in the absence of a radio signal the location where the magnetization "flips" is stationary with respect to the coil, so there is no flux change and no voltage is induced in the pickup coil.

text: Néel studied at the Lycée du Parc in Lyon and was accepted at the École Normale Supérieure in Paris. He obtained the degree of Doctor of Science at the University of Strasbourg. He was corecipient (with the Swedish astrophysicist Hannes Alfvén) of the Nobel Prize for Physics in 1970 for his pioneering studies of the magnetic properties of solids. His contributions to solid state physics have found numerous useful applications, particularly in the development of improved computer memory units. About 1930 he suggested that a new form of magnetic behavior might exist; called antiferromagnetism, as opposed to ferromagnetism. Above a certain temperature (the Néel temperature) this behaviour stops. Néel pointed out (1948) that materials could also exist showing ferrimagnetism. Néel has also given an explanation of the weak magnetism of certain rocks, making possible the study of the history of Earth's magnetic field.

text: Néel studied at the

text: Lycée du Parc

text: in

text: Lyon

text: and was accepted at the

text: École Normale Supérieure

text: in

text: Paris

text: . He obtained the degree of Doctor of Science at the

text: University of Strasbourg

text: . He was corecipient (with the

text: Swedish

text: astrophysicist

text: Hannes Alfvén

text: ) of the

text: Nobel Prize

text: for

text: Physics

text: in 1970 for his pioneering studies of the magnetic properties of

text: solid

text: s. His contributions to

text: solid state physics

text: have found numerous useful applications, particularly in the development of improved

text: computer

text: memory units. About 1930 he suggested that a new form of magnetic behavior might exist; called

text: antiferromagnetism

text: , as opposed to

text: ferromagnetism

text: . Above a certain temperature (the

text: Néel temperature

text: ) this behaviour stops. Néel pointed out (1948) that materials could also exist showing

text: ferrimagnetism

text: . Néel has also given an explanation of the weak magnetism of certain rocks, making possible the study of the history of

text: Earth's magnetic field

text: The rotor's magnetic field may be produced by permanent magnets, or by a field coil electromagnet. Automotive alternators use a rotor winding which allows control of the alternator's generated voltage by varying the current in the rotor field winding.  Permanent magnet machines avoid the loss due to magnetizing current in the rotor, but are restricted in size, due to the cost of the magnet material.  Since the permanent magnet field is constant, the terminal voltage varies directly with the speed of the generator.  Brushless AC generators are usually larger than those used in automotive applications.

text: The Earth's magnetic field has two main components.  The stronger component known as the Earth’s poles, reverses direction at irregular intervals.  The weaker variations are the Earth’s magnetic map.  Within these weaker areas the local directions and intensities change gradually (secular variation).   A compass does not point to the true North Pole but to direction that is a function of the North Magnetic Pole and the local secular variation to yield a magnetic declination.The magnetic declination at any given time can be frozen into a clay formation that contains magnetite and is heated above the Curie point.  In general, many cultures used long-term fire hearths made of clay bricks, or a space lined with clay, that were baked into place by use.  These artifacts of occupation can yield the magnetic declination from the last time they were fired or used.Archaeomagnetic dating was described in the 1992 publication “Paleomagnetism: Magnetic Domains to Geologic Terranes.” By Robert F. Butler.

text: The

text: Earth's magnetic field

text: has two main components.  The stronger component known as the Earth’s poles, reverses direction at irregular intervals.  The weaker variations are the Earth’s magnetic map.  Within these weaker areas the local directions and intensities change gradually (secular variation).   A compass does not point to the true

text: North Pole

text: but to direction that is a function of the

text: North Magnetic Pole

text: and the local secular variation to yield a

text: magnetic declination

text: .The magnetic declination at any given time can be frozen into a clay formation that contains magnetite and is heated above the

text: Curie point

text: .  In general, many cultures used long-term fire hearths made of clay bricks, or a space lined with clay, that were baked into place by use.  These artifacts of occupation can yield the magnetic declination from the last time they were fired or used.Archaeomagnetic dating was described in the 1992 publication “Paleomagnetism: Magnetic Domains to Geologic Terranes.” By Robert F. Butler.

text: Magnetoreception (also magnetoception) is a sense which allows an organism to detect a magnetic field to perceive direction, altitude or location. This sensory modality is used by a range of animals for orientation and navigation, and as a method for animals to develop regional maps. For the purpose of navigation, magnetoreception deals with the detection of the Earth's magnetic field.

text: Magnetoreception (also magnetoception) is a

text: sense

text: which allows an

text: organism

text: to detect a

text: magnetic field

text: to perceive direction, altitude or location. This sensory modality is used by a range of animals for orientation and

text: navigation

text: , and as a method for animals to develop regional maps. For the purpose of navigation, magnetoreception deals with the detection of the

text: Earth's magnetic field

text: Some kinds of remanence  are undesirable and must be removed before the useful remanence is measured. One is isothermal remanent magnetization (IRM), which as a component of NRM induced through exposing a particle to a large magnetic field, causing the field to flip its lower coercivity magnetic moments to a field-favored direction.  A commonly cited mechanism of IRM acquisition is through lightning strikes.  Another is viscous remanent magnetization (VRM), a remanence acquired when the rock sits in the Earth's field for long periods.

text: Some kinds of remanence  are undesirable and must be removed before the useful remanence is measured. One is

text: isothermal remanent magnetization

text: (IRM), which as a component of NRM induced through exposing a particle to a large magnetic field, causing the field to flip its lower coercivity magnetic moments to a field-favored direction.  A commonly cited mechanism of IRM acquisition is through lightning strikes.  Another is

text: viscous remanent magnetization

text: (VRM), a remanence acquired when the rock sits in the Earth's field for long periods.

text: The Earth's magnetic field varies over a wide range of timescales. The longer-term variations, typically occurring over decades to millennia, are predominantly the result of dynamo action in the Earth's core. Geomagnetic variations on timescales of seconds to years also occur, due to dynamic processes in the ionosphere, magnetosphere and heliosphere. These changes are ultimately tied to variations associated with the solar activity (or sunspot) cycle and are manifestations of space weather.

text: The Earth's magnetic field varies over a wide range of timescales. The longer-term variations, typically occurring over decades to millennia, are predominantly the result of dynamo action in the Earth's core. Geomagnetic variations on timescales of seconds to years also occur, due to dynamic processes in the

text: ionosphere

text: magnetosphere

text: and

text: heliosphere

text: . These changes are ultimately tied to variations associated with the

text: solar activity (or sunspot) cycle

text: and are manifestations of space weather.

text: The ring current around Earth produces a magnetic field that is directly opposite Earth's magnetic field, i.e. if the difference between solar electrons and protons gets higher, then Earth's magnetic field becomes weaker.

text: Non contact type TPS work on the principle of Hall effect or Inductive sensors, or magnetoresistive technologies, wherein generally the magnet or inductive loop is the dynamic part which is mounted on the butterfly valve throttle spindle/shaft gear and the sensor & signal processing circuit board is mounted within the ETC gear box cover and is stationary. When the magnet/inductive loop mounted on the spindle which is rotated from the lower mechanical stop to WOT, there is a change in the magnetic field for the sensor. The change in the magnetic field is sensed by the sensor and the voltage generated is given as the input to the ECU. Normally a two pole rare earth magnet is used for the TPS due to their high Curie temperatures required in the under-hood vehicle environment. The magnet may be of diametrical type, ring type, rectangular or segment type. The magnet is defined to have a certain magnetic field that does not vary significantly with time or temperature.In case of failure of the TPS operation the CHECK ENGINE light remains illuminated even if there is no problem or error in the ECU. It cannot be corrected by clearing ECU errors by running diagnostic software. In order to rectify the malfunction the TPS needs to be replaced by a new one.

text: Non contact type TPS work on the principle of

text: Hall effect

text: or

text: Inductive sensor

text: s, or

text: magnetoresistive

text: technologies, wherein generally the magnet or inductive loop is the dynamic part which is mounted on the butterfly valve throttle spindle/shaft gear and the sensor & signal processing circuit board is mounted within the ETC gear box cover and is stationary. When the magnet/inductive loop mounted on the spindle which is rotated from the lower mechanical stop to WOT, there is a change in the magnetic field for the sensor. The change in the magnetic field is sensed by the sensor and the voltage generated is given as the input to the ECU. Normally a two pole

text: rare earth magnet

text: is used for the TPS due to their high

text: Curie temperature

text: s required in the under-hood vehicle environment. The magnet may be of diametrical type, ring type, rectangular or segment type. The magnet is defined to have a certain magnetic field that does not vary significantly with time or temperature.In case of failure of the TPS operation the CHECK ENGINE light remains illuminated even if there is no problem or error in the ECU. It cannot be corrected by clearing ECU errors by running diagnostic software. In order to rectify the malfunction the TPS needs to be replaced by a new one.

text: In both induction and synchronous motors, the AC power supplied to the motor's stator creates a magnetic field that rotates in time with the AC oscillations.  Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a slower speed than the stator field.  The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor.  This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding, when the latter is short-circuited or closed through an external impedance.  The rotating magnetic flux induces currents in the windings of the rotor;  in a manner similar to currents induced in a transformer's secondary winding(s).  The currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field.   Due to Lenz's Law, the direction of the magnetic field created will be such as to oppose the change in current through the rotor windings.  The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied load. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slower than synchronous speed. The difference, or "slip," between actual and synchronous speed varies from about 0.5 to 5.0% for standard Design B torque curve induction motors.  The induction machine's essential character is that it is created solely by induction instead of being separately excited as in synchronous or DC machines or being self-magnetized as in permanent magnet motors.

text: In both induction and

text: synchronous motor

text: s, the AC power supplied to the motor's

text: stator

text: creates a

text: magnetic field

text: that rotates in time with the AC oscillations.  Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a slower speed than the stator field.  The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor.  This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding, when the latter is short-circuited or closed through an external impedance.  The rotating

text: magnetic flux

text: induces currents in the windings of the rotor;  in a manner similar to currents induced in a

text: transformer

text: 's secondary winding(s).  The currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field.   Due to

text: Lenz's Law

text: , the direction of the magnetic field created will be such as to oppose the change in current through the rotor windings.  The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied load. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slower than synchronous speed. The difference, or "slip," between actual and synchronous speed varies from about 0.5 to 5.0% for standard Design B torque curve induction motors.  The induction machine's essential character is that it is created solely by induction instead of being separately excited as in synchronous or DC machines or being self-magnetized as in

text: permanent magnet motors

text: Earth's magnetosphere is shaped by the impact of the solar wind on the Earth's magnetic field. This forms an obstacle to the flow, diverting it, at an average distance of about 70,000 km (11 Earth radii or Re), producing a bow shock 12,000 km to 15,000 km (1.9 to 2.4 Re) further upstream. The width of the magnetosphere abreast of Earth, is typically 190,000 km (30 Re), and on the night side a long "magnetotail" of stretched field lines extends to great distances (> 200 Re).The high latitude magnetosphere is filled with plasma as the solar wind passes the Earth. The flow of plasma into the magnetosphere increases with additional turbulence, density and speed in the solar wind. This flow is favoured by a southward component of the IMF, which can then directly connect to the high latitude geomagnetic field lines. The flow pattern of magnetospheric plasma is mainly from the magnetotail toward the Earth, around the Earth and back into the solar wind through the magnetopause on the day-side. In addition to moving perpendicular to the Earth's magnetic field, some magnetospheric plasma travels down along the Earth's magnetic field lines, gains additional energy and loses it to the atmosphere in the auroral zones. The cusps of the magnetosphere, separating geomagnetic field lines that close through the Earth from those that close remotely allow a small amount of solar wind to directly reach the top of the atmosphere, producing an auroral glow.On 26 February 2008, THEMIS probes were able to determine, for the first time, the triggering event for the onset of magnetospheric substorms. Two of the five probes, positioned approximately one third the distance to the moon, measured events suggesting a magnetic reconnection event 96 seconds prior to auroral intensification.

text: Earth's

text: magnetosphere

text: is shaped by the impact of the solar wind on the Earth's magnetic field. This forms an obstacle to the flow, diverting it, at an average distance of about 70,000 km (11 Earth radii or Re), producing a

text: bow shock

text: 12,000 km to 15,000 km (1.9 to 2.4 Re) further upstream. The width of the magnetosphere abreast of Earth, is typically 190,000 km (30 Re), and on the night side a long "magnetotail" of stretched field lines extends to great distances (> 200 Re).The high latitude magnetosphere is filled with plasma as the solar wind passes the Earth. The flow of plasma into the magnetosphere increases with additional turbulence, density and speed in the solar wind. This flow is favoured by a southward component of the IMF, which can then directly connect to the high latitude geomagnetic field lines. The flow pattern of magnetospheric plasma is mainly from the magnetotail toward the Earth, around the Earth and back into the solar wind through the

text: magnetopause

text: on the day-side. In addition to moving perpendicular to the Earth's magnetic field, some magnetospheric plasma travels down along the Earth's magnetic field lines, gains additional energy and loses it to the atmosphere in the auroral zones. The cusps of the magnetosphere, separating geomagnetic field lines that close through the Earth from those that close remotely allow a small amount of solar wind to directly reach the top of the atmosphere, producing an auroral glow.On 26 February 2008,

text: THEMIS

text: probes were able to determine, for the first time, the triggering event for the onset of

text: magnetospheric substorm

text: s. Two of the five probes, positioned approximately one third the distance to the moon, measured events suggesting a

text: magnetic reconnection

text: event 96 seconds prior to auroral intensification.

text: The inductive-discharge ignition system operates according to the rules of electromagnetism described by Faraday's Law of Induction which states that the induction of electromotive force (emf) in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit. In other words, the emf generated is proportional to the rate of change of the magnetic flux. More simply stated, an electric field is induced in any system in which a magnetic field is changing with time. The change could be changes in direction of force or strength. The effects described by this law are those by which generators, motors, alternators, and transformers function. There are two main concepts to be taken from Faraday's Law that apply to the design of inductive discharge ignitions. One is that moving a wire through a magnetic field will induce an electric voltage and current in the wire, aka electromagnetic induction. The second is that current moving in a wire will induce a magnetic field around the wire.

text: The inductive-discharge ignition system operates according to the rules of

text: electromagnetism

text: described by

text: Faraday's Law of Induction

text: which states that the

text: induction

text: of

text: electromotive force

text: (emf) in any

text: closed circuit

text: is equal to the

text: time

text: rate of change of the

text: magnetic flux

text: through the

text: circuit

text: . In other words, the emf generated is

text: proportional

text: to the rate of change of the magnetic flux. More simply stated, an

text: electric field

text: is induced in any system in which a

text: magnetic field

text: is changing with time. The change could be changes in

text: direction

text: of

text: force

text: or strength. The effects described by this law are those by which

text: generators

text: motors

text: alternators

text: , and

text: transformer

text: s function. There are two main

text: concept

text: s to be taken from Faraday's Law that apply to the design of inductive discharge ignitions. One is that moving a

text: wire

text: through a

text: magnetic field

text: will induce an

text: electric

text: voltage

text: and

text: current

text: in the wire, aka

text: electromagnetic induction

text: . The second is that current moving in a wire will induce a magnetic field around the wire.

text: A sea-going metal-hulled ship or submarine, by its very nature, develops a magnetic signature as it travels, due to a magneto-mechanical interaction with Earth's magnetic field. It also picks up the magnetic orientation of the earth's magnetic field where it is built. This signature can be exploited by magnetic mines or facilitate the detection of a submarine by ships or aircraft with magnetic anomaly detection (MAD) equipment. Navies use the deperming procedure, in conjunction with degaussing, as a countermeasure against this.

text: A sea-going metal-hulled ship or submarine, by its very nature, develops a magnetic signature as it travels, due to a magneto-mechanical interaction with Earth's magnetic field. It also picks up the magnetic orientation of the earth's magnetic field where it is built. This signature can be exploited by magnetic mines or facilitate the detection of a submarine by ships or aircraft with

text: magnetic anomaly detection (MAD)

text: equipment.

text: Navies

text: use the deperming procedure, in conjunction with degaussing, as a countermeasure against this.

text: is the length of hypothetical wire through which the test current flows. The magnetic field exerts a force on all magnets including, for example, those used in compasses. The fact that the Earth's magnetic field is aligned closely with the orientation of the Earth's axis causes compass magnets to become oriented because of the magnetic force pulling on the needle.

text: is the length of hypothetical wire through which the test current flows. The magnetic field exerts a force on all

text: magnet

text: s including, for example, those used in

text: compass

text: es. The fact that the

text: Earth's magnetic field

text: is aligned closely with the orientation of the Earth's

text: axis

text: causes compass magnets to become oriented because of the magnetic force pulling on the needle.

text: The Earth's magnetic field is thought to be produced by convection currents in the outer liquid of Earth's core. The Dynamo theory proposes that these movements produce electric currents that, in turn, produce the magnetic field.

text: The Earth's magnetic field is thought to be produced by convection currents in the outer liquid of Earth's core. The

text: Dynamo theory

text: proposes that these movements produce electric currents that, in turn, produce the magnetic field.

text: Mercury's magnetic field is approximately a magnetic dipole (meaning the field has only two magnetic poles)  apparently global, on planet Mercury. Data from Mariner 10 led to its discovery in 1974; the spacecraft measured the field's strength as 1.1% that of Earth's magnetic field. The origin of the magnetic field can be explained by dynamo theory,.  The magnetic field is strong enough near the bow shock to slow the solar wind, which induces a magnetosphere.

text: Mercury's magnetic field is approximately a magnetic

text: dipole

text: (meaning the field has only two magnetic poles)  apparently global, on

text: planet Mercury

text: . Data from

text: Mariner 10

text: led to its discovery in 1974; the spacecraft measured the field's strength as 1.1% that of

text: Earth's magnetic field

text: . The origin of the magnetic field can be explained by

text: dynamo theory

text: ,.  The magnetic field is strong enough near the

text: bow shock

text: to slow the

text: solar wind

text: , which induces a

text: magnetosphere

text: Due to the lower overall fields, an RFP reactor might not need superconducting magnets.  This is a large advantage over tokamaks since superconducting magnets are delicate and expensive and so must be shielded from the Neutron rich fusion environment.  RFPs are susceptible to surface instabilities and so require a close fitting shell.  Some experiments (such as the Madison Symmetric Torus) use their close fitting shell as a magnetic coil by driving current through the shell itself.  This is attractive from a reactor standpoint since a solid copper shell (for example) would be fairly robust against high energy neutrons, compared with superconducting magnets.  There is also no established beta limit for RFPs.  There exists a possibility that a reversed field pinch could achieve ignition solely with ohmic power (by driving current through the plasma and generating heat from electrical resistance, rather than through electron cyclotron resonance heating), which would be much simpler than tokamak designs, though it could not be operated in steady state.

text: Due to the lower overall fields, an RFP reactor might not need superconducting magnets.  This is a large advantage over tokamaks since superconducting magnets are delicate and expensive and so must be shielded from the Neutron rich fusion environment.  RFPs are susceptible to surface instabilities and so require a close fitting shell.  Some experiments (such as the

text: Madison Symmetric Torus

text: ) use their close fitting shell as a magnetic coil by driving current through the shell itself.  This is attractive from a reactor standpoint since a solid copper shell (for example) would be fairly robust against high energy neutrons, compared with superconducting magnets.  There is also no established

text: beta

text: limit for RFPs.  There exists a possibility that a reversed field pinch could achieve ignition solely with

text: ohmic power

text: (by driving current through the plasma and generating heat from electrical resistance, rather than through

text: electron cyclotron resonance

text: heating), which would be much simpler than tokamak designs, though it could not be operated in steady state.

text: Alternatively, introductory treatments of magnetism introduce the Biot–Savart law, which describes the magnetic field associated with an electric current. An observer at rest with respect to a system of static, free charges will see no magnetic field. However, a moving observer looking at the same set of charges does perceive a current, and thus a magnetic field.  That is, the magnetic field is simply the electric field, as seen in a moving coordinate system.

text: Alternatively, introductory treatments of

text: magnetism

text: introduce the

text: Biot–Savart law

text: , which describes the magnetic field associated with an

text: electric current

text: . An observer at rest with respect to a system of static, free charges will see no magnetic field. However, a moving observer looking at the same set of charges does perceive a current, and thus a magnetic field.  That is, the magnetic field is simply the electric field, as seen in a moving coordinate system.

text: It is sometimes useful to model the magnetic dipole similar to the electric dipole with two equal but opposite magnetic charges (one south the other north) separated by distance . This model produces an -field not a -field. Such a model is deficient, though, both in that there are no magnetic charges and in that it obscures the link between electricity and magnetism. Further, as discussed above it fails to explain the inherent connection between angular momentum and magnetism.

text: It is sometimes useful to model the magnetic dipole similar to the electric dipole with two equal but opposite magnetic charges (one south the other north) separated by distance . This model produces an -field not a -field. Such a model is deficient, though, both in that there are no magnetic charges and in that it obscures the link between electricity and magnetism. Further, as discussed above it fails to explain the inherent connection between

text: angular momentum

text: and magnetism.

text: The solution to the static convergence and purity problems is a set of color alignment magnets installed around the neck of the CRT. These movable weak permanent magnets are usually mounted on the back end of the deflection yoke assembly and are set at the factory to compensate for any static purity and convergence errors that are intrinsic to the unadjusted tube. Typically there are two or three pairs of two magnets in the form of rings made of plastic impregnated with a magnetic material, with their magnetic fields parallel to the planes of the magnets, which are perpendicular to the electron gun axes. Each pair of magnetic rings forms a single effective magnet whose field vector can be fully and freely adjusted (in both direction and magnitude). By rotating a pair of magnets relative to each other, their relative field alignment can be varied, adjusting the effective field strength of the pair. (As they rotate relative to each other, each magnet's field can be considered to have two opposing components at right angles, and these four components [two each for two magnets] form two pairs, one pair reinforcing each other and the other pair opposing and canceling each other. Rotating away from alignment, the magnets' mutually reinforcing field components decrease as they are traded for increasing opposed, mutually cancelling components.) By rotating a pair of magnets together, preserving the relative angle between them, the direction of their collective magnetic field can be varied. Overall, adjusting all of the convergence/purity magnets allows a finely tuned slight electron beam deflection or lateral offset to be applied, which compensates for minor static convergence and purity errors intrinsic to the uncalibrated tube. Once set, these magnets are usually glued in place, but normally they can be freed and readjusted in the field (e.g. by a TV repair shop) if necessary.

text: The solution to the static convergence and purity problems is a set of color alignment magnets installed around the neck of the CRT. These movable weak permanent magnets are usually mounted on the back end of the deflection yoke assembly and are set at the factory to compensate for any static purity and convergence errors that are intrinsic to the unadjusted tube. Typically there are two or three pairs of two magnets in the form of rings made of plastic impregnated with a magnetic material, with their

text: magnetic fields

text: parallel to the planes of the magnets, which are perpendicular to the electron gun axes. Each pair of magnetic rings forms a single effective magnet whose field

text: vector

text: The magnetic field strength of white dwarfs in intermediate polar systems are typically 1 million to 10 million gauss (100–1000 teslas).  This is about a million times stronger than the Earth's magnetic field and towards the upper limit of magnetic field strengths that can be produced in a laboratory on Earth, but is much less than the magnetic field strength of neutron stars.  At the intersection of the accretion stream and the surface of the white dwarf, a hot spot is produced.  Because the white dwarf has a dipole magnetic field, it will have one hot spot at each of its magnetic poles.  As the white dwarf and its dipole magnetic field spin, the hot spots will spin also.

text: The

text: magnetic field

text: strength of white dwarfs in intermediate polar systems are typically 1 million to 10 million gauss (100–1000

text: tesla

text: s).  This is about a million times stronger than the

text: Earth's magnetic field

text: and towards the upper limit of magnetic field strengths that can be produced in a laboratory on Earth, but is much less than the magnetic field strength of

text: neutron star

text: s.  At the intersection of the accretion stream and the surface of the white dwarf, a hot spot is produced.  Because the white dwarf has a

text: dipole

text: magnetic field, it will have one hot spot at each of its magnetic poles.  As the white dwarf and its dipole magnetic field spin, the hot spots will spin also.

text: The strength and direction of magnetic fields and electric currents can be measured using a "magnetoresistive barber-pole sensor" (also called a "hermetic proximity sensor"), and its performance can be depicted using a mathematical formula. Such a sensor interleaves a series of permanent magnet strips with a series of magnetoresistive strips. The "conductive barberpole strips are canted across the sensor and connect one magnetoresistive strip, over a permanent magnet strip, to another magnetoresistive strip." This is said to provide a "uniform magnetic field throughout the sensor" thereby enhancing its resistance to external magnetic fields. The technology is used in wireless sensor networks which "have gathered a lot of attention as an important research domain" and were "deployed in many applications, e.g., navigation, military, ambient intelligence, medical, and industrial tasks. Context-based processing and services, in particular location-context, are of key interest ..." (See Music (acoustic illusion), infra.)

text: The strength and direction of

text: magnetic fields and electric currents

text: can be measured using a "

text: magnetoresistive

text: barber-pole sensor" (also called a "hermetic proximity sensor"), and its performance can be depicted using a mathematical formula. Such a sensor interleaves a series of permanent magnet strips with a series of magnetoresistive strips. The "conductive barberpole strips are canted across the sensor and connect one magnetoresistive strip, over a permanent magnet strip, to another magnetoresistive strip." This is said to provide a "uniform

text: magnetic field

text: throughout the sensor" thereby enhancing its resistance to external magnetic fields. The technology is used in

text: wireless sensor networks

text: which "have gathered a lot of attention as an important research domain" and were "deployed in many applications, e.g.,

text: navigation

text: , military,

text: ambient intelligence

text: , medical, and industrial tasks. Context-based processing and services, in particular location-context, are of key interest ..." (See Music (acoustic illusion), infra.)

text: Magnetars are characterized by their extremely powerful magnetic fields of 10 to 10 tesla. These magnetic fields are hundreds of millions of times stronger than any man-made magnet, and quadrillions of times more powerful than the field surrounding Earth. Earth has a geomagnetic field of 30–60 microteslas, and a neodymium-based, rare-earth magnet has a field of about 1.25 tesla, with a magnetic energy density of 4.0×10 J/m. A magnetar's 10 tesla field, by contrast, has an energy density of 4.0×10 J/m, with an E/c mass density >10 times that of lead. The magnetic field of a magnetar would be lethal even at a distance of 1000 km due to the strong magnetic field distorting the electron clouds of the subject's constituent atoms, rendering the chemistry of life impossible.  At a distance of halfway from earth to the moon, a magnetar could strip information from the magnetic stripes of all credit cards on Earth. , they are the most powerful magnetic objects detected throughout the universe.

text: Magnetars are characterized by their extremely powerful magnetic fields of 10 to 10

text: tesla

text: . These magnetic fields are hundreds of millions of times stronger than any man-made magnet, and quadrillions of times more powerful than

text: the field surrounding Earth

text: . Earth has a

text: geomagnetic

text: field of 30–60 microteslas, and a

text: neodymium-based, rare-earth magnet

text: has a field of about 1.25 tesla, with a magnetic energy density of 4.0×10 J/m. A magnetar's 10 tesla field, by contrast, has an energy density of 4.0×10 J/m, with an

text: E/c

text: mass density >10 times that of

text: lead

text: . The magnetic field of a magnetar would be lethal even at a distance of 1000 km due to the strong magnetic field distorting the electron clouds of the subject's constituent atoms, rendering the chemistry of life impossible.  At a distance of halfway from earth to the moon, a magnetar could strip information from the magnetic stripes of all

text: credit card

text: s on Earth. , they are the most powerful magnetic objects detected throughout the universe.

text: This device measures the strength of the Earth's magnetic field in one direction.  For measurements on all three axes, the device would consist of three orthogonal magnetometers. Given the spacecraft's position, the magnetic field measurements can be compared to a known magnetic field which is given by the International Geomagnetic Reference Field model. Measurements made by magnetometers are affected by noise consisting of alignment error, scale factor errors, and spacecraft electrical activity.  For near Earth orbits, the error in the modeled field direction may vary from 0.5 degrees near the Equator to 3 degrees near the magnetic poles, where erratic auroral currents play a large role. The limitation of such a device is that in orbits far from Earth, the magnetic field is too weak and is actually dominated by the interplanetary field which is complicated and unpredictable.

text: This device measures the strength of the

text: Earth's magnetic field

text: in one direction.  For measurements on all three axes, the device would consist of three orthogonal

text: magnetometers

text: . Given the spacecraft's position, the magnetic field measurements can be compared to a known magnetic field which is given by the

entity_name: International Geomagnetic Reference Field

text: International Geomagnetic Reference Field

text: model. Measurements made by magnetometers are affected by noise consisting of alignment error, scale factor errors, and spacecraft electrical activity.  For near Earth orbits, the error in the modeled field direction may vary from 0.5 degrees near the Equator to 3 degrees near the magnetic poles, where erratic auroral currents play a large role. The limitation of such a device is that in orbits far from Earth, the magnetic field is too weak and is actually dominated by the interplanetary field which is complicated and unpredictable.

text: For example, SQUIDs are being used as detectors to perform magnetic resonance imaging (MRI). While high-field MRI uses precession fields of one to several teslas, SQUID-detected MRI uses measurement fields that lie in the microtesla range. In a conventional MRI system, the signal scales as the square of the measurement frequency (and hence precession field): one power of frequency comes from the thermal polarization of the spins at ambient temperature, while the second power of field comes from the fact that the induced voltage in the pickup coil is proportional to the frequency of the precessing magnetization. In the case of untuned SQUID detection of prepolarized spins, however, the NMR signal strength is independent of precession field, allowing MRI signal detection in extremely weak fields, of order the Earth's field. SQUID-detected MRI has advantages over high-field MRI systems, such as the low cost required to build such a system, and its compactness. The principle has been demonstrated by imaging human extremities, and its future application may include tumor screening.

text: For example, SQUIDs are being used as detectors to perform

text: magnetic resonance imaging

text: (MRI). While high-field MRI uses precession fields of one to several teslas, SQUID-detected MRI uses measurement fields that lie in the microtesla range. In a conventional MRI system, the signal scales as the square of the measurement frequency (and hence precession field): one power of frequency comes from the thermal polarization of the spins at ambient temperature, while the second power of field comes from the fact that the induced voltage in the pickup coil is proportional to the frequency of the precessing magnetization. In the case of untuned SQUID detection of prepolarized spins, however, the NMR signal strength is independent of precession field, allowing MRI signal detection in extremely weak fields, of order the Earth's field. SQUID-detected MRI has advantages over high-field MRI systems, such as the low cost required to build such a system, and its compactness. The principle has been demonstrated by imaging human extremities, and its future application may include tumor screening.

text: The magnetic field strength at Saturn's equator is about 21 μT (0.21 G), which corresponds to a dipole magnetic moment of about 4.6 T•m. This makes Saturn's magnetic field slightly weaker than Earth's; however, its magnetic moment is about 580 times larger. Saturn's magnetic dipole is strictly aligned with its rotational axis, meaning that the field, uniquely, is highly axisymmetric. The dipole is slightly shifted (by 0.037 R) along Saturn's rotational axis towards the north pole.

text: The magnetic field strength at Saturn's equator is about 21

text: μT

text: G

text: ), which corresponds to a dipole

text: magnetic moment

text: of about 4.6

text: T

text: m

text: . This makes Saturn's magnetic field slightly weaker than Earth's; however, its magnetic moment is about 580 times larger. Saturn's magnetic dipole is strictly aligned with its rotational axis, meaning that the field, uniquely, is highly axisymmetric. The dipole is slightly shifted (by 0.037 R) along Saturn's rotational axis towards the north pole.

text: A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a T-Tauri phase in which the solar wind would have had a magnetic field orders of magnitude larger than the present solar wind. However, much of the field may have been screened out by the Earth's mantle. An alternative source is currents in the core-mantle boundary driven by chemical reactions or variations in thermal or electric conductivity. Such effects may still provide a small bias that are part of the boundary conditions for the geodynamo.

text: A dynamo can amplify a magnetic field, but it needs a "seed" field to get it started. For the Earth, this could have been an external magnetic field. Early in its history the Sun went through a

text: T-Tauri phase

text: in which the

text: solar wind

text: would have had a magnetic field orders of magnitude larger than the present solar wind. However, much of the field may have been screened out by the Earth's mantle. An alternative source is currents in the core-mantle boundary driven by chemical reactions or variations in thermal or electric conductivity. Such effects may still provide a small bias that are part of the boundary conditions for the geodynamo.

text: Magnetic Sensors, commonly referred to as compasses detect magnetic fields and measure their absolute position relative to Earth’s magnetic north and nearby magnetic materials. Information from magnetic sensors can also be used to correct errors from other sensors such as accelerometers. One example of how compass sensors are used in consumer devices is reorienting a displayed map to match up with the general direction a user is facing.

text: Magnetic Sensors, commonly referred to as

text: compasses

text: detect magnetic fields and measure their absolute position relative to Earth’s magnetic north and nearby magnetic materials. Information from magnetic sensors can also be used to correct errors from other sensors such as accelerometers. One example of how compass sensors are used in consumer devices is reorienting a displayed map to match up with the general direction a user is facing.

text: Another hypothesis by McCormac and Evans assumes that the Earth's field would disappear entirely during reversals. They argue that the atmosphere of Mars may have been eroded away by the solar wind because it had no magnetic field to protect it. They predict that ions would be stripped away from Earth's atmosphere above 100 km. However, the evidence from paleointensity measurements is that the magnetic field does not disappear. Based on paleointensity data for the last 800,000 years, the magnetopause is still estimated to be at about 3 Earth radii during the Brunhes-Matuyama reversal. Even if the magnetic field disappeared, the solar wind may induce a sufficient magnetic field in the Earth's ionosphere to shield the surface from energetic particles.

text: Another hypothesis by McCormac and Evans assumes that the Earth's field would disappear entirely during reversals. They argue that the atmosphere of Mars may have been eroded away by the

text: solar wind

text: because it had no magnetic field to protect it. They predict that ions would be stripped away from Earth's atmosphere above 100 km. However, the evidence from paleointensity measurements is that the magnetic field does not disappear. Based on paleointensity data for the last 800,000 years, the

text: magnetopause

text: is still estimated to be at about 3 Earth radii during the

text: Brunhes-Matuyama reversal

text: . Even if the magnetic field disappeared, the

text: solar wind

text: may induce a sufficient magnetic field in the Earth's

text: ionosphere

text: to shield the surface from energetic particles.

text: Shielding makes use of the electrical principle of the Faraday cage. The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from external electrical fields, particularly if the shield is connected to a point of constant voltage, such as earth or ground. Simple shielding of this type is not greatly effective against low-frequency magnetic fields, however - such as magnetic "hum" from a nearby power transformer. A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation.

text: Shielding makes use of the electrical principle of the

text: Faraday cage

text: . The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from external electrical fields, particularly if the shield is connected to a point of constant voltage, such as

text: earth or ground

text: . Simple shielding of this type is not greatly effective against low-frequency magnetic fields, however - such as magnetic "hum" from a nearby power

text: transformer

text: . A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation.

text: Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field. Only recently have advances in materials technology allowed the creation of high-intensity permanent magnets, such as neodymium magnets, allowing the development of compact, high-power motors without the extra real-estate of field coils and excitation means. But as these high performance permanent magnets become more applied in electric motor or generator systems, other problems are realized (see Permanent magnet synchronous generator).

text: Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field. Only recently have advances in materials technology allowed the creation of high-intensity permanent magnets, such as

text: neodymium magnets

text: , allowing the development of compact, high-power motors without the extra real-estate of field coils and excitation means. But as these high performance permanent magnets become more applied in electric motor or generator systems, other problems are realized (see

text: Permanent magnet synchronous generator

text: In the late 1590s Henry Briggs, a professor of geometry at Gresham College in London, had published a table of magnetic inclination with latitude for the earth. It agreed well with the inclinations that Gilbert measured around the circumference of his terella. Gilbert deduced that the Earth's magnetic field is equivalent to that of a uniformly magnetized sphere, magnetized parallel to the axis of rotation (in modern terms, a geocentric axial dipole). However, he was aware that declinations were not consistent with this model. Based on the declinations that were known at the time, he proposed that the continents, because of their raised topography, formed centers of attraction that made compass needles deviate. He even demonstrated this effect by gouging out some topography on his terella and measuring the effect on declinations. A Jesuit monk, Niccolò Cabeo, later took a leaf from Gilbert's book and showed that, if the topography was on the correct scale for the Earth, the differences between the highs and lows would only be about one tenth of a millimeter. Therefore, the continents could not noticeably affect the declination.

text: In the late 1590s

text: Henry Briggs

text: , a professor of geometry at

text: Gresham College

text: in London, had published a table of magnetic inclination with latitude for the earth. It agreed well with the inclinations that Gilbert measured around the circumference of his terella. Gilbert deduced that the Earth's magnetic field is equivalent to that of a uniformly magnetized sphere, magnetized parallel to the

text: axis of rotation

text: (in modern terms, a geocentric axial dipole). However, he was aware that declinations were not consistent with this model. Based on the declinations that were known at the time, he proposed that the continents, because of their raised

text: topography

text: , formed centers of attraction that made compass needles deviate. He even demonstrated this effect by gouging out some topography on his terella and measuring the effect on declinations. A

text: Jesuit

text: monk,

text: Niccolò Cabeo

text: , later took a leaf from Gilbert's book and showed that, if the topography was on the correct scale for the Earth, the differences between the highs and lows would only be about one tenth of a millimeter. Therefore, the continents could not noticeably affect the declination.

text: Earth's magnetic field is used by geologists to determine subterranean rock structures. For the most part, these geodetic surveyors are searching for oil, gas or mineral deposits. They can accomplish this only when Earth's field is quiet, so that true magnetic signatures can be detected. Other geophysicists prefer to work during geomagnetic storms, when strong variations in the Earth's normal subsurface electric currents allow them to sense subsurface oil or mineral structures. This technique is called magnetotellurics. For these reasons, many surveyors use geomagnetic alerts and predictions to schedule their mapping activities.

text: Earth's magnetic field is used by geologists to determine subterranean rock structures. For the most part, these geodetic surveyors are searching for oil, gas or mineral deposits. They can accomplish this only when Earth's field is quiet, so that true magnetic signatures can be detected. Other geophysicists prefer to work during geomagnetic storms, when strong variations in the Earth's normal subsurface electric currents allow them to sense subsurface oil or mineral structures. This technique is called

text: magnetotellurics

text: . For these reasons, many surveyors use geomagnetic alerts and predictions to schedule their mapping activities.

text: An X-ray pulsar consists of a magnetized neutron star in orbit with a normal stellar companion and is a type of binary star system. The magnetic-field strength at the surface of the neutron star is typically about 10 Tesla, over a trillion times stronger than the strength of the magnetic field measured at the surface of the Earth (60 µT).

text: An X-ray pulsar consists of a magnetized

text: neutron star

text: in orbit with a normal stellar companion and is a type of

text: binary star system

text: . The

text: magnetic-field

text: strength at the surface of the neutron star is typically about 10

text: Tesla

text: , over a trillion times stronger than the strength of the magnetic field measured at the

text: surface of the Earth

text: µT

text: The ions and electrons of a plasma interacting with the Earth's magnetic field generally follow its magnetic field lines.  These represent the force that a north magnetic pole would experience at any given point.  (Denser lines indicate a stronger force.)  Plasmas exhibit more complex second-order behaviors, studied as part of magnetohydrodynamics.

text: The

text: ion

text: s and

text: electron

text: s of a

text: plasma

text: interacting with the

text: Earth's magnetic field

text: generally follow its

text: magnetic field lines

text: .  These represent the force that a north magnetic pole would experience at any given point.  (Denser lines indicate a stronger force.)  Plasmas exhibit more complex second-order behaviors, studied as part of

text: magnetohydrodynamics

text: During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury's magnetic field can be extremely "leaky". The spacecraft encountered magnetic "tornadoes" – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to  wide or a third of the radius of the planet.  These twisted magnetic flux tubes, technically known as flux transfer events, form open windows in the planet's magnetic shield through which the solar wind may enter and directly impact Mercury's surface via magnetic reconnection This also occurs in Earth's magnetic field. The MESSENGER observations showed the reconnection rate is ten times higher at Mercury, but its proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER.

text: During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury's magnetic field can be extremely "leaky". The spacecraft encountered magnetic "tornadoes" – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to  wide or a third of the radius of the planet.  These twisted magnetic flux tubes, technically known as

text: flux transfer event

text: s, form open windows in the planet's magnetic shield through which the solar wind may enter and directly impact Mercury's surface via

text: magnetic reconnection

text: This also occurs in Earth's magnetic field. The MESSENGER observations showed the reconnection rate is ten times higher at Mercury, but its proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER.

text: In 1832, the German mathematician Carl Friedrich Gauss, assisted by Wilhelm Weber, implicitly defined the second as a base unit when he quoted the earth's magnetic field in terms of millimetres, grams, and seconds.  Prior to this, the strength of the earth’s magnetic field had only been described in relative terms.  The technique used by Gauss was to equate the torque induced on a suspended magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length and time to the magnetic field.

text: In 1832, the German

text: mathematician

text: Carl Friedrich Gauss

text: , assisted by

text: Wilhelm Weber

text: , implicitly defined the second as a base unit when he quoted the earth's magnetic field in terms of millimetres, grams, and seconds.  Prior to this, the strength of the earth’s magnetic field had only been described in

text: relative terms

text: .  The technique used by Gauss was to equate the

text: torque

text: induced on a suspended magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length and time to the magnetic field.

text: Earth's magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of Mars, resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.

text: Earth's magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation. One stripping mechanism is for gas to be caught in bubbles of magnetic field, which are ripped off by solar winds. Calculations of the loss of carbon dioxide from the atmosphere of

text: Mars

text: , resulting from scavenging of ions by the solar wind, indicate that the dissipation of the magnetic field of Mars caused a near total loss of its atmosphere.

text: A rock is a mixture of minerals, each with its own Curie temperature; the authors therefore looked for a spectrum of temperatures rather than a single temperature. In the ideal sample, the PDC did not raise the temperature of the fragment beyond the highest blocking temperature. Some constituent material retained the magnetism imposed by the Earth's field when the item was formed. The temperature was raised above the lowest blocking temperature and therefore some minerals on recooling acquired the magnetism of the Earth as it was in 79 AD. The overall field of the sample was the vector sum of the fields of the high-blocking material and the low-blocking material.

text: A

text: rock

text: is a mixture of minerals, each with its own Curie temperature; the authors therefore looked for a

text: spectrum

text: of temperatures rather than a single temperature. In the ideal sample, the PDC did not raise the temperature of the fragment beyond the highest blocking temperature. Some constituent material retained the magnetism imposed by the Earth's field when the item was formed. The temperature was raised above the lowest blocking temperature and therefore some minerals on recooling acquired the magnetism of the Earth as it was in 79 AD. The overall field of the sample was the

text: vector sum

text: of the fields of the high-blocking material and the low-blocking material.

text: The dipole is tilted roughly 10° from Jupiter's axis of rotation; the tilt is similar to that of the Earth (11.3°). Its equatorial field strength is about 428 μT (4.28 G), which corresponds to a dipole magnetic moment of about 1.56 T·m. This makes Jupiter's magnetic field 10 times stronger than Earth's, and its magnetic moment about 18,000 times larger. Jupiter's magnetic field rotates at the same speed as the region below its atmosphere, with a period of 9 h 55 m. No changes in its strength or structure have been observed since the first measurements were taken by the Pioneer spacecraft in the mid-1970s.

text: The dipole is tilted roughly 10° from Jupiter's axis of rotation; the tilt is similar to that of the Earth (11.3°). Its equatorial field strength is about 428

text: μT

text: G

text: ), which corresponds to a dipole

text: magnetic moment

text: of about 1.56

text: T

text: m

text: . This makes Jupiter's magnetic field 10 times stronger than Earth's, and its magnetic moment about 18,000 times larger. Jupiter's magnetic field

text: rotates

text: at the same speed as the region below its atmosphere, with a period of 9 h 55 m. No changes in its strength or structure have been observed since the first measurements were taken by the

text: Pioneer

text: spacecraft in the mid-1970s.

text: For the comparison of two currents these are fed through two wires which are led through a superconducting tube. The Meissner effect induces a screening current on the inner surface of the tube, flowing opposite to and being exactly as large as the sum of the currents inside the tube. Thus, this shielding current exactly cancels the magnetic field inside the tube produced by the currents in the wires. The screening current flows back across the outer surface of the tube, giving rise to a magnetic field in the room outside of the tube. This field is detected by a highly sensitive magnetometer, acting as a null detector. The signal of this null detector thus is a measure for the equality of the currents; in particular it is zero if the two currents are of exactly equal magnitude. The important and crucial point characterizing the CCC is the fact that the magnitude of the screening current and its distribution on the surface of the superconducting screen are independent of the position and the path of the wires inside the tube.

text: For the comparison of two currents these are fed through two wires which are led through a superconducting tube. The Meissner effect induces a screening current on the inner surface of the tube, flowing opposite to and being exactly as large as the sum of the currents inside the tube. Thus, this shielding current exactly cancels the

text: magnetic field

text: inside the tube produced by the currents in the wires. The screening current flows back across the outer surface of the tube, giving rise to a magnetic field in the room outside of the tube. This field is detected by a highly sensitive

text: magnetometer

text: , acting as a null detector. The signal of this null detector thus is a measure for the equality of the currents; in particular it is zero if the two currents are of exactly equal magnitude. The important and crucial point characterizing the CCC is the fact that the magnitude of the screening current and its distribution on the surface of the superconducting screen are independent of the position and the path of the wires inside the tube.

text: The Space Science Directorate of the South African National Space Agency, previously the Hermanus Magnetic Observatory (HMO), is a research facility of the National Research Foundation, and forms part of the worldwide network which monitors variations of the earth's magnetic field.

text: The

text: Space Science Directorate

text: of the

text: South African National Space Agency

text: , previously the

text: Hermanus Magnetic Observatory

text: (HMO), is a research facility of the

entity_name: National Research Foundation of South Africa

text: National Research Foundation

text: , and forms part of the worldwide network which monitors variations of the

text: earth's magnetic field

text: A magnetometer is a device that senses magnetic field strength and, when used in a three-axis triad, magnetic field direction. As a spacecraft navigational aid, sensed field strength and direction is compared to a map of Earth's magnetic field stored in the memory of an on-board or ground-based guidance computer. If spacecraft position is known then attitude can be inferred.

text: A

text: magnetometer

text: is a device that senses

text: magnetic field

text: strength and, when used in a three-axis triad, magnetic field direction. As a spacecraft navigational aid, sensed field strength and direction is compared to a map of

text: Earth's magnetic field

text: stored in the memory of an on-board or ground-based guidance computer. If spacecraft position is known then attitude can be inferred.

text: Planetary magnetic poles are defined analogously to the Earth's North and South magnetic poles: they are the locations on the planet's surface at which the planet's magnetic field lines are vertical. The direction of the field determines whether the pole is a magnetic north or south pole, exactly as on Earth. The Earth's magnetic axis is approximately aligned with its rotational axis, meaning that the magnetic poles are relatively close to the geographic poles. However, this is not necessarily the case for other planets; the magnetic axis of Uranus, for example, is inclined by as much as 60°.

text: Planetary magnetic poles are defined analogously to the Earth's

text: North

text: and

text: South magnetic pole

text: s: they are the locations on the planet's surface at which the planet's

text: magnetic field

text: lines are vertical. The direction of the field determines whether the pole is a magnetic north or south pole, exactly as on Earth. The Earth's magnetic axis is approximately aligned with its rotational axis, meaning that the magnetic poles are relatively close to the geographic poles. However, this is not necessarily the case for other planets; the magnetic axis of

text: Uranus

text: , for example, is inclined by as much as 60°.

text: Equipment using large magnets or generating magnetic fields, or any similar environment, must be avoided by patients with an ICD.  As with other metallic objects, an ICD is a contraindication to the use of magnetic resonance imaging (MRI).

text: Equipment using large magnets or generating magnetic fields, or any similar environment, must be avoided by patients with an ICD.  As with other metallic objects, an ICD is a

text: contraindication

text: to the use of

text: magnetic resonance imaging

text: (MRI).

text: The first magnetic self-protection equipment was developed at the beginning of World War II because of the advent of magnetically detonated mines. This was initially a cable which was placed along the entire length to the hull of the vessel and the application of direct current produced a magnetic field that counteracted the magnetic field of the steel mass of the vessel.

text: The first magnetic self-protection equipment was developed at the beginning of

text: World War II

text: because of the advent of magnetically detonated mines. This was initially a cable which was placed along the entire length to the hull of the vessel and the application of direct current produced a magnetic field that counteracted the magnetic field of the steel mass of the vessel.

text: The high permeability of mu-metal provides a low reluctance path for magnetic flux, leading to its use in magnetic shields against static or slowly varying magnetic fields. Magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the magnetic field lines around the shielded area. Thus, the best shape for shields is a closed container surrounding the shielded space. The effectiveness of mu-metal shielding decreases with the alloy's permeability, which drops off at both low field strengths and, due to saturation, at high field strengths. Thus, mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at such low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, reducing them to a lower level that can be shielded effectively by the inner mu-metal layers.

text: The high permeability of mu-metal provides a low

text: reluctance

text: path for

text: magnetic flux

text: , leading to its use in

text: magnetic shields

text: against static or slowly varying magnetic fields. Magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the

text: magnetic field line

text: s around the shielded area. Thus, the best shape for shields is a closed container surrounding the shielded space. The effectiveness of mu-metal shielding decreases with the alloy's permeability, which drops off at both low field strengths and, due to

text: saturation

text: , at high field strengths. Thus, mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at such low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, reducing them to a lower level that can be shielded effectively by the inner mu-metal layers.

text: The dCompass is a compass sensor for Mindstorms NXT.  This compact sensor detects magnetic fields for navigation and works on all three axis.  Using a magnetic sensor, the sensor is able to measure the earth's magnetic field and returns a magnetic heading, telling you which way your robot is heading.  The device can be used without calibration or, if needed, can be calibrated with software to account for magnetic fields to deliver a highly accurate compass heading.  The sensor is supported in NXT-G, Labview, and ROBOTC.  The sensor communicates with the NXT via I2C and can be placed on any port.

text: The dCompass is a

text: compass

text: sensor for Mindstorms NXT.  This compact sensor detects

text: magnetic fields

text: for

text: navigation

text: and works on all three axis.  Using a magnetic sensor, the sensor is able to measure the earth's magnetic field and returns a magnetic

text: heading

text: , telling you which way your robot is heading.  The device can be used without

text: calibration

text: or, if needed, can be calibrated with software to account for magnetic fields to deliver a highly accurate compass heading.  The sensor is supported in NXT-G, Labview, and

text: ROBOTC

text: .  The sensor communicates with the NXT via I2C and can be placed on any port.

text: The figure is a sketch of Earth's magnetic field represented by field lines. For most locations, the magnetic field has a significant up/down component in addition to the north/south component.  (There is also an east/west component, as Earth's magnetic and geographical poles do not coincide.) The magnetic field can be visualised as a bar magnet buried deep in Earth's interior.

text: A Helmholtz coil is a device for producing a region of nearly uniform magnetic field, named after the German physicist Hermann von Helmholtz. It consists of two solenoid electromagnets on the same axis.  Besides creating magnetic fields, Helmholtz coils are also used in scientific apparatus to cancel external magnetic fields, such as the Earth's magnetic field.

text: A Helmholtz coil is a device for producing a region of nearly uniform

text: magnetic field

text: , named after the German physicist

text: Hermann von Helmholtz

text: . It consists of two

text: solenoid

text: electromagnet

text: s on the same axis.  Besides creating magnetic fields, Helmholtz coils are also used in scientific apparatus to cancel external magnetic fields, such as the Earth's magnetic field.

text: At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North is the declination () or variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination () or magnetic dip. The intensity () of the field is proportional to the force it exerts on a magnet. Another common representation is in  (North),  (East) and  (Down) coordinates.

text: At any location, the Earth's magnetic field can be represented by a three-dimensional vector. A typical procedure for measuring its direction is to use a compass to determine the direction of magnetic North. Its angle relative to true North is the declination () or variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination () or

text: magnetic dip

text: . The intensity () of the field is proportional to the force it exerts on a magnet. Another common representation is in  (North),  (East) and  (Down) coordinates.

text: From 1903, when Størmer first observed Kristian Birkeland's experimental attempts to explain the aurora borealis, he was fascinated by aurorae and related phenomena. His first work on the subject attempted to model mathematically the paths taken by charged particles perturbed by the influence of a magnetized sphere, and Størmer eventually published over 48 papers on the motion of charged particles. By modeling the problem using differential equations and polar coordinates, Størmer was able to show that the radius of curvature of any particle's path is proportional to the square of its distance from the sphere's center. To solve the resulting differential equations numerically, he used Verlet integration, which is therefore also known as Störmer's method. Ernst Brüche and Willard Harrison Bennett verified experimentally Størmer's predicted particle motions; Bennett called his experimental apparatus "Störmertron" in honor of Størmer. Størmer's calculations showed that small variations in the trajectories of particles approaching the earth would be magnified by the effects of the Earth's magnetic field, explaining the convoluted shapes of aurorae. Størmer also considered the possibility that particles might be trapped within the magnetic field, and worked out the orbits of these trapped particles, a prediction that was borne out after his death by the 1958 discovery of the Van Allen radiation belt.

text: From 1903, when Størmer first observed

text: Kristian Birkeland

text: 's experimental attempts to explain the

text: aurora borealis

text: , he was fascinated by aurorae and related phenomena. His first work on the subject attempted to model mathematically the paths taken by charged particles perturbed by the influence of a

text: magnet

text: ized

text: sphere

text: , and Størmer eventually published over 48 papers on the motion of charged particles. By modeling the problem using

text: differential equation

text: s and

text: polar coordinate

text: s, Størmer was able to show that the

text: radius of curvature

text: of any particle's path is proportional to the square of its distance from the sphere's center. To solve the resulting differential equations numerically, he used

text: Verlet integration

text: , which is therefore also known as Störmer's method.

text: Ernst Brüche

text: and

text: Willard Harrison Bennett

text: verified experimentally Størmer's predicted particle motions; Bennett called his experimental apparatus "Störmertron" in honor of Størmer. Størmer's calculations showed that small variations in the trajectories of particles approaching the earth would be magnified by the effects of the Earth's magnetic field, explaining the convoluted shapes of aurorae. Størmer also considered the possibility that particles might be trapped within the magnetic field, and worked out the orbits of these trapped particles, a prediction that was borne out after his death by the 1958 discovery of the

text: Van Allen radiation belt

text: Mapping the magnetic field of an object is simple in principle. First, measure the strength and direction of the magnetic field at a large number of locations (or at every point in space). Then, mark each location with an arrow (called a vector) pointing in the direction of the local magnetic field with its magnitude proportional to the strength of the magnetic field.

text: Mapping the magnetic field of an object is simple in principle. First, measure the strength and direction of the magnetic field at a large number of locations (or at every point in space). Then, mark each location with an arrow (called a

text: vector

text: ) pointing in the direction of the local magnetic field with its magnitude proportional to the strength of the magnetic field.

text: The post-nesting migration of adult female green sea turtles from Ascension to Brazil has been recorded using satellite transmitters as part of an experiment into their navigation. In addition to the transmitters, some turtles were fitted with magnets which were expected to disrupt any ability to use the Earth's field for navigation. In fact there was no difference in migratory performance between these turtles and turtles which weren't carrying magnets, but the experimental design has been criticised. In fact there is strong evidence that green turtles are sensitive to magnetic cues. For example, juvenile green turtles exposed to fields north and south of a capture site (i.e. displaced in geomagnetic but not geographical space) oriented in a direction that would have led them back to the capture site, suggesting that they can use the earth's magnetic field to acquire positional information. Adult turtles also use magnetic cues. Whilst geomagnetic cues may guide navigation over long distances, close to the goal, it is thought that turtles use wind-borne cues emanating from the goal to home in on their target. Most recently, it has been shown that juvenile greens can orient using a 'sun compass' In other words, they can use directional information to determine their headings.

text: Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. It is also the measure of that magnetization. Colloquially, when a magnet is "magnetized" it has remanence.  The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism.

text: Remanence or remanent magnetization or residual magnetism is the

text: magnetization

text: left behind in a

text: ferromagnetic

text: material (such as

text: iron

text: ) after an external

text: magnetic field

text: is removed. It is also the measure of that magnetization. Colloquially, when a magnet is "magnetized" it has remanence.  The remanence of magnetic materials provides the magnetic memory in

text: magnetic storage

text: devices, and is used as a source of information on the past Earth's magnetic field in

text: paleomagnetism

text: Many studies have also shown that moths navigate. One study showed that many moths may use the Earth's magnetic field to navigate, as a study of the moth heart and dart suggests. Another study, of the migratory behavior of the silver Y, showed, even at high altitudes, the species can correct its course with changing winds, and prefers flying with favourable winds, suggesting a great sense of direction. Aphrissa statira in Panama loses its navigational capacity when exposed to a magnetic field, suggesting it uses the Earth's magnetic field.

text: Many studies have also shown that moths navigate. One study showed that many moths may use the

text: Earth's magnetic field

text: to navigate, as a study of the moth

text: heart and dart

text: suggests. Another study, of the migratory behavior of the

text: silver Y

text: , showed, even at high altitudes, the species can correct its course with changing winds, and prefers flying with favourable winds, suggesting a great sense of direction.

text: Aphrissa statira

text: in

text: Panama

text: loses its navigational capacity when exposed to a magnetic field, suggesting it uses the Earth's magnetic field.

text: It is sometimes more convenient to express the magnetic field in terms of magnetic latitude and distance in earth radii.  The magnetic latitude

text: The Earth's magnetic field lines arc high above the Earth until they reach the magnetic conjugate area in the opposite hemisphere.

text: Dead reckoning, navigating from a known position using only information about one's own speed and direction, was suggested by Charles Darwin in 1873 as a possible mechanism. In the 20th century, Karl von Frisch showed that honey bees can navigate by the sun, by the polarization pattern of the blue sky, and by the earth's magnetic field; of these, they rely on the sun when possible. William Tinsley Keeton showed that homing pigeons could similarly make use of a range of navigational cues, including the sun, earth's magnetic field, olfaction and vision. Ronald Lockley demonstrated that a species of small seabird, the Manx shearwater, could orient themselves and fly home at full speed, when released far from home, provided either the sun or the stars were visible.

text: Dead reckoning

text: , navigating from a known position using only information about one's own speed and direction, was suggested by

text: Charles Darwin

text: in 1873 as a possible mechanism. In the 20th century,

text: Karl von Frisch

text: showed that honey bees can navigate by the sun, by the polarization pattern of the blue sky, and by the earth's magnetic field; of these, they rely on the sun when possible.

text: William Tinsley Keeton

text: showed that

text: homing pigeons

text: could similarly make use of a range of navigational cues, including the sun,

text: earth's magnetic field

text: olfaction

text: and vision.

text: Ronald Lockley

text: demonstrated that a species of small seabird, the Manx shearwater, could orient themselves and fly home at full speed, when released far from home, provided either the sun or the stars were visible.

text: Earth’s magnetic fields are used for migration for a wide variety of species including  bacteria, mollusks, arthropods, mammals, birds, reptiles, and amphibians. In order to understand the Earth’s magnetic fields, the earth can be viewed as a large magnet. As a typical magnet has a north and south end, so does the earth. The north pole magnet is located at the Earth’s north pole and the south pole magnet is located at the Earth’s south pole. From this north and south pole span magnetic fields. The magnetic field leaves the poles and curves around the earth until it reaches the opposite pole.

text: These first loudspeakers used electromagnets, because large, powerful permanent magnets were generally not available at a reasonable price. The coil of an electromagnet, called a field coil, was energized by current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a choke coil, filtering the power supply of the amplifier that the loudspeaker was connected to. AC ripple in the current was attenuated by the action of passing through the choke coil. However, AC line frequencies tended to modulate the audio signal going to the voice coil and added to the audible hum. In 1930 Jensen introduced the first commercial fixed-magnet loudspeaker; however, the large, heavy iron magnets of the day were impractical and field-coil speakers remained predominant until the widespread availability of lightweight Alnico magnets after World War II.

text: These first loudspeakers used

text: electromagnet

text: s, because large, powerful

text: permanent magnet

text: s were generally not available at a reasonable price. The coil of an electromagnet, called a field coil, was energized by current through a second pair of connections to the driver. This winding usually served a dual role, acting also as a

text: choke coil

text: , filtering the

text: power supply

text: of the

text: amplifier

text: that the loudspeaker was connected to. AC ripple in the current was attenuated by the action of passing through the choke coil. However, AC line frequencies tended to modulate the audio signal going to the voice coil and added to the audible hum. In 1930

text: Jensen

text: introduced the first commercial fixed-magnet loudspeaker; however, the large, heavy iron magnets of the day were impractical and field-coil speakers remained predominant until the widespread availability of lightweight

text: Alnico

text: magnets after World War II.

text: It measures the change in anisotropic magnetoresistance caused by an external magnetic field in the Hall geometry. The sensor responds to magnetic field components in the sensor plane as opposed to the ordinary Hall sensor, which measures field components perpendicular to the sensor plane. Hence the name "planar Hall". Generally speaking, for ferromagnetic materials, the resistance is larger when the current flows along the direction of magnetization than when it flows perpendicular to the magnetization vector. This creates an asymmetric electric field perpendicular to the current, which depends on the magnetization state of the sensor. Exactly controlling the magnetization state is the key to the operation of the planar Hall sensor. From fabrication the magnetization is confined to one certain direction in zero applied field, and the application of a field perpendicular to this direction changes the magnetization state in such a way that the electronic readout is linear with respect to the magnitude of the applied field. This is true for applied fields smaller than a fourth of the intrinsic effective anisotropy field (see ref. 1 for details on the working principle).

text: It measures the change in anisotropic

text: magnetoresistance

text: In some applications, a Helmholtz coil is used to cancel out the Earth's magnetic field, producing a region with a magnetic field intensity much closer to zero.

text: In some applications, a Helmholtz coil is used to cancel out the

text: Earth's magnetic field

text: , producing a region with a magnetic field intensity much closer to zero.

text: Near the surface of the Earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the center of the Earth and tilted at an angle of about 11° with respect to the rotational axis of the Earth. The dipole is roughly equivalent to a powerful bar magnet, with its south pole pointing towards the geomagnetic North Pole. This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels the north poles, it must be attracted to the south pole of Earth's magnet. The dipolar field accounts for 80–90% of the field in most locations.

text: Near the surface of the Earth, its magnetic field can be closely approximated by the field of a

text: magnetic dipole

text: positioned at the center of the Earth and tilted at an angle of about 11° with respect to the

text: rotational axis

text: of the Earth. The dipole is roughly equivalent to a powerful bar

text: magnet

text: , with its south pole pointing towards the

text: geomagnetic North Pole

text: . This may seem surprising, but the north pole of a magnet is so defined because, if allowed to rotate freely, it points roughly northward (in the geographic sense). Since the north pole of a magnet attracts the south poles of other magnets and repels the north poles, it must be attracted to the south pole of Earth's magnet. The dipolar field accounts for 80–90% of the field in most locations.

text: where the integral can be over all space or, equivalently, where  is nonzero.Magnetic potential energy is the form of energy related not only to the distance between magnetic materials, but also to the orientation, or alignment, of those materials within the field. For example, the needle of a compass has the lowest magnetic potential energy when it is aligned with the north and south poles of the Earth's magnetic field. If the needle is moved by an outside force, torque is exerted on the magnetic dipole of the needle by the Earth's magnetic field, causing it to move back into alignment. The magnetic potential energy of the needle is highest when its field is in the same direction as the Earth's magnetic field. Two magnets will have potential energy in relation to each other and the distance between them, but this also depends on their orientation. If the opposite poles are held apart, the potential energy will be the highest when they are near the edge of their attraction, and the lowest when they pull together. Conversely, like poles will have the highest potential energy when forced together, and the lowest when they spring apart.

text: Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 T. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a superconducting magnet (1 T is about 20,000 times the Earth's magnetic field).

text: Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 T. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a

text: superconducting magnet

text: (1 T is about 20,000 times the

text: Earth's magnetic field

text: Magnetic damping can be observed easily due to the development of strong magnets made of neodymium and other rare earth metals.  To observe magnetic damping with a minimum of materials and effort, use any length of copper tubing and a neodymium magnet with a smaller diameter than the tube.  Ideally the neodymium magnet will have a diameter only slightly smaller than the tube to maximize the magnetic field.  Hold the tube vertically and drop the magnet through it to see magnetic damping at work.

text: In contrast, permanent ferrite magnets are made of hard ferrites, which have a high coercivity and high remanence after magnetization. Iron oxide and barium or strontium carbonate are used in manufacturing of hard ferrite magnets. The high coercivity means the materials are very resistant to becoming demagnetized, an essential characteristic for a permanent magnet.  They also have high magnetic permeability.  These so-called ceramic magnets are cheap, and are widely used in household products such as refrigerator magnets. The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30 to 160 kiloampere turns per meter (400 to 2000 oersteds). The density of ferrite magnets is about 5 g/cm.

text: In contrast, permanent ferrite

text: magnet

text: s are made of hard ferrites, which have a high

text: coercivity

text: and high

text: remanence

text: after magnetization.

text: Iron oxide

text: and

text: barium

text: or

text: strontium carbonate

text: are used in manufacturing of hard ferrite magnets. The high coercivity means the materials are very resistant to becoming demagnetized, an essential characteristic for a permanent magnet.  They also have high

text: magnetic permeability

text: .  These so-called ceramic magnets are cheap, and are widely used in household products such as

text: refrigerator magnet

text: s. The maximum magnetic field B is about 0.35

text: tesla

text: and the magnetic field strength H is about 30 to 160 kiloampere turns per meter (400 to 2000

text: oersted

text: s). The density of ferrite magnets is about 5 g/cm.

text: Over Earth's equator, the magnetic field lines become almost horizontal, then return to reconnect at high latitudes. However, at high altitudes, the magnetic field is significantly distorted by the solar wind and its solar magnetic field. On the dayside of Earth, the magnetic field is significantly compressed by the solar wind to a distance of approximately . Earth's bow shock is about  thick and located about  from Earth. The magnetopause exists at a distance of several hundred kilometers above Earth's surface. Earth's magnetopause has been compared to a sieve because it allows solar wind particles to enter. Kelvin–Helmholtz instabilities occur when large swirls of plasma travel along the edge of the magnetosphere at a different velocity from the magnetosphere, causing the plasma to slip past. This results in magnetic reconnection, and as the magnetic field lines break and reconnect, solar wind particles are able to enter the magnetosphere. On Earth's nightside, the magnetic field extends in the magnetotail, which lengthwise exceeds . Earth's magnetotail is the primary source of the polar aurora. Also, NASA scientists have suggested that Earth's magnetotail might cause "dust storms" on the Moon by creating a potential difference between the day side and the night side.

text: Over Earth's

text: equator

text: , the magnetic field lines become almost horizontal, then return to reconnect at high latitudes. However, at high altitudes, the magnetic field is significantly distorted by the solar wind and its solar magnetic field. On the dayside of Earth, the magnetic field is significantly compressed by the solar wind to a distance of approximately . Earth's bow shock is about  thick and located about  from Earth. The magnetopause exists at a distance of several hundred kilometers above Earth's surface. Earth's magnetopause has been compared to a

text: sieve

text: because it allows solar wind particles to enter.

text: Kelvin–Helmholtz instabilities

text: occur when large swirls of plasma travel along the edge of the magnetosphere at a different velocity from the magnetosphere, causing the plasma to slip past. This results in

text: magnetic reconnection

text: , and as the magnetic field lines break and reconnect, solar wind particles are able to enter the magnetosphere. On Earth's nightside, the magnetic field extends in the magnetotail, which lengthwise exceeds . Earth's magnetotail is the primary source of the

text: polar aurora

text: . Also, NASA scientists have suggested that Earth's magnetotail might cause "dust storms" on the Moon by creating a potential difference between the day side and the night side.

text: Halo grounds and ring grounds are placed around the areas to be protected so that the magnetic field will encounter these conductors first. Energy from the magnetic field creates currents in the halo and ring ground, and this current is then safely shunted into the earth so that it does not harm equipment inside the protected building. Since most of the energy in the magnetic field is used up in the creation of these currents, very little energy is left over to create damaging currents inside the protected building.

text: The history of geomagnetism is concerned with the history of the study of Earth's magnetic field. It encompasses the history of navigation using compasses, studies of the prehistoric magnetic field (archeomagnetism and paleomagnetism), and applications to plate tectonics.

text: The history of geomagnetism is concerned with the history of the study of

text: Earth's magnetic field

text: . It encompasses the history of navigation using

text: compass

text: es, studies of the prehistoric magnetic field (archeomagnetism and

text: paleomagnetism

text: ), and applications to

text: plate tectonics

text: Halley also hoped that careful observations of magnetic deviations could provide a determination of longitude.  The magnetic field of the Earth was not well understood at the time.  Mariners had observed that magnetic north deviated from geographic north in many locations.  Halley and others hoped that the pattern of deviation, if consistent, could be used to determine longitude.  If the measured deviation matched that recorded on a chart, the position would be known.  Halley used his voyages on the pink Paramour to study the magnetic variance and was able to provide maps showing the halleyan or isogonic lines.  This method was eventually to fail as the localized variations from general magnetic trends make the method unreliable.

text: Halley also hoped that careful observations of

text: magnetic deviation

text: s could provide a determination of longitude.  The magnetic field of the Earth was not well understood at the time.  Mariners had observed that

text: magnetic north

text: deviated from

text: geographic north

text: in many locations.  Halley and others hoped that the pattern of deviation, if consistent, could be used to determine longitude.  If the measured deviation matched that recorded on a chart, the position would be known.  Halley used his voyages on the

text: pink

text: Paramour

text: to study the magnetic variance and was able to provide maps showing the halleyan or

text: isogonic

text: lines.  This method was eventually to fail as the localized variations from general magnetic trends make the method unreliable.

text: The profile of the ionosphere is highly variable, changing constantly on timescales of minutes, hours, days, seasons, and years. This profile becomes even more complex near Earth's magnetic poles, where the nearly vertical alignment and intensity of earth's magnetic field can cause physical effects like aurorae.

text: The profile of the ionosphere is highly variable, changing constantly on timescales of minutes, hours, days, seasons, and years. This profile becomes even more complex near Earth's magnetic poles, where the nearly vertical alignment and intensity of earth's magnetic field can cause physical effects like

text: aurorae

text: The demagnetizing field, also called the stray field, is the magnetic field (H-field) generated by the magnetization in a magnet. The total magnetic field in a region containing magnets is the sum of the demagnetizing fields of the magnets and the magnetic field due to any free currents or displacement currents. The term demagnetizing field reflects its tendency to act on the magnetization so as to reduce the total magnetic moment. It gives rise to shape anisotropy in ferromagnets with a single magnetic domain and to magnetic domains in larger ferromagnets.

text: The demagnetizing field, also called the stray field, is the

text: magnetic field

text: (H-field) generated by the

text: magnetization

text: in a

text: magnet

text: . The total magnetic field in a region containing magnets is the sum of the demagnetizing fields of the magnets and the magnetic field due to any

text: free current

text: s or

text: displacement current

text: s. The term demagnetizing field reflects its tendency to act on the magnetization so as to reduce the total

text: magnetic moment

text: . It gives rise to shape anisotropy in

text: ferromagnets

text: with a

text: single magnetic domain

text: and to

text: magnetic domains

text: in larger ferromagnets.

text: The magnetic field source in MAF is typically an electromagnet or a rare earth permanent magnet. Preferably a permanent magnet is used due to the high energy density, lack of overheating resulting in a constant flux density, low cost, ease of integration into existing CNC equipment, and for simplicity. However some applications require the need to adjust the flux density during finishing or require a switching magnetic field which is only attainable with an electromagnet since the magnetic field in a permanent magnet cannot simply be switched off.

text: The basic principle of pulsed EPR is similar to NMR spectroscopy. Differences can be found in the relative size of the magnetic interactions and in the relaxation rates which are orders of magnitudes larger in EPR than NMR. A full description of the theory is given within the quantum mechanical formalism, but since the magnetization is being measured as a bulk property, a more intuitive picture can be obtained with a classical description. For a better understanding of the concept of pulsed EPR let us consider the effects on the magnetization vector in the laboratory frame as well as in the rotating frame. As the animation below shows, in the laboratory frame the static magnetic field B is assumed to be parallel to the z-axis and the microwave field B parallel to the x-axis. When an electron spin is placed in magnetic field it experiences a torque which causes its magnetic moment to precess around the magnetic field. The precession frequency is known as the Larmor frequency ω (see page 18 of ref ).

text: The basic principle of pulsed EPR is similar to NMR spectroscopy. Differences can be found in the relative size of the magnetic interactions and in the relaxation rates which are orders of magnitudes larger in EPR than NMR. A full description of the theory is given within the quantum mechanical formalism, but since the magnetization is being measured as a bulk property, a more intuitive picture can be obtained with a classical description. For a better understanding of the concept of pulsed EPR let us consider the effects on the magnetization vector in the

text: laboratory frame

text: as well as in the

text: rotating frame

text: . As the animation below shows, in the laboratory frame the static magnetic field B is assumed to be parallel to the z-axis and the microwave field B parallel to the x-axis. When an electron spin is placed in magnetic field it experiences a torque which causes its

text: magnetic moment

text: to precess around the magnetic field. The precession frequency is known as the

text: Larmor frequency

text: ω (see page 18 of ref ).

text: Low field NMR spans a range of different nuclear magnetic resonance (NMR) modalities, going from NMR conducted in permanent magnets, supporting magnetic fields of a few T, all the way down to zero field NMR, where the Earth's field is carefully shielded such that magnetic fields of nT are achieved where nuclear spin precession is close to zero. In a broad sense, "Low-field NMR" is the branch of nuclear magnetic resonance that is NOT conducted in superconducting high-field magnets. Low field NMR also includes Earth's field NMR where simply the Earth's field is exploited to cause nuclear spin-precession which is detected. With magnetic fields on the order of μT and below magnetometers such as SQUIDs or atomic magnetometers (among others) are used as detectors. "Normal" high field NMR relies on the detection of spin-precession with inductive detection with a simple coil. However, this detection modality becomes less sensitive as the magnetic field and the associated frequencies decrease. Hence the push toward alternative detection methods at very low fields.

text: Low field NMR spans a range of different

text: nuclear magnetic resonance

text: (NMR) modalities, going from NMR conducted in permanent magnets, supporting magnetic fields of a few T, all the way down to

text: zero field NMR

text: , where the Earth's field is carefully shielded such that magnetic fields of

text: nT

text: are achieved where nuclear spin precession is close to zero. In a broad sense, "Low-field NMR" is the branch of

text: nuclear magnetic resonance

text: that is NOT conducted in superconducting high-field magnets. Low field NMR also includes

text: Earth's field NMR

text: where simply the Earth's field is exploited to cause nuclear spin-precession which is detected. With magnetic fields on the order of

text: μT

text: and below

text: magnetometer

text: s such as

text: SQUID

text: s or atomic magnetometers (among others) are used as detectors. "Normal" high field NMR relies on the detection of spin-precession with inductive detection with a simple coil. However, this detection modality becomes less sensitive as the magnetic field and the associated frequencies decrease. Hence the push toward alternative detection methods at very low fields.

text: The Earth's magnetic field strength was measured by Carl Friedrich Gauss in 1835 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years. The Magsat satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later Ørsted satellite allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of S. Africa.

text: The Earth's magnetic field strength was measured by

text: Carl Friedrich Gauss

text: in 1835 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years. The

text: Magsat

text: satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later

text: Ørsted satellite

text: allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of S. Africa.

text: This notion of magnetic navigational skills was first observed in a 2005 study conducted by Esquivel et al. on a S. quadripunctata nest near Rio de Janeiro, Brazil. The study applied various levels of applied magnetic fields across the entrance of the nest. The exiting angles (both vertical and horizontal) of the individual bees were then measured as they emerged from the nest. The primary control experiment confirmed that the majority of the nest had a preferential exiting angle in accordance with the local geomagnetic field. Over the course of four months, the study group measured the two angles in comparison to various magnitudes of applied magnetic fields and compared them to observed angles in natural geomagnetic fields. A significant correlation was found between the two, definitively showing that the stingless bee relies on magnetoreception for navigational purposes.

text: This notion of magnetic navigational skills was first observed in a 2005 study conducted by Esquivel et al. on a S. quadripunctata nest near Rio de Janeiro, Brazil. The study applied various levels of applied magnetic fields across the entrance of the nest. The exiting angles (both vertical and horizontal) of the individual bees were then measured as they emerged from the nest. The primary control experiment confirmed that the majority of the nest had a preferential exiting angle in accordance with the local

text: geomagnetic

text: field. Over the course of four months, the study group measured the two angles in comparison to various magnitudes of applied magnetic fields and compared them to observed angles in natural geomagnetic fields. A significant correlation was found between the two, definitively showing that the stingless bee relies on

text: magnetoreception

text: for navigational purposes.

text: Bats may also use magnetic fields to orient themselves. While it is known that bats use echolocation to navigate over short distances, it is unclear how they navigate over longer distances. When Eptesicus fuscus are taken from their home roosts and exposed to magnetic fields 90 degrees clockwise or counterclockwise of magnetic north, they are disoriented and set off for their homes in the wrong direction. Therefore, it seems that Eptesicus fuscus is capable of magnetoreception. However, the exact use of magnetic fields by Eptesicus fuscus is unclear as the magnetic field could be used either as a map, a compass, or a compass calibrator. Recent research with another bat species, Myotis myotis, supports the hypothesis that bats use magnetic fields as a compass calibrator and their primary compass is the sun.

text: Bats may also use magnetic fields to orient themselves. While it is known that bats use

text: echolocation

text: to navigate over short distances, it is unclear how they navigate over longer distances. When

text: Eptesicus fuscus

text: are taken from their home roosts and exposed to magnetic fields 90 degrees clockwise or counterclockwise of magnetic north, they are disoriented and set off for their homes in the wrong direction. Therefore, it seems that Eptesicus fuscus is capable of magnetoreception. However, the exact use of magnetic fields by Eptesicus fuscus is unclear as the magnetic field could be used either as a map, a compass, or a compass calibrator. Recent research with another bat species,

text: Myotis myotis

text: , supports the hypothesis that bats use magnetic fields as a compass calibrator and their primary compass is the sun.

text: The secondary payloads were four CubeSats that were deployed from the CMS. Three of them were PhoneSats, 1U CubeSats built by NASA's Ames Research Center. These were named Alexander, Graham and Bell, after the inventor of the telephone. The purpose of these three satellites was to demonstrate the use of smartphones as avionics in CubeSats. They each had a mass of  and were powered by lithium batteries. The fourth nanosat was a 3U CubeSat, called Dove-1, built by Cosmogia Inc. It carried a "technology development Earth imagery experiment" using the Earth's magnetic field for attitude control.

text: The secondary payloads were four

text: CubeSat

text: s that were deployed from the CMS. Three of them were

text: PhoneSat

text: s, 1U CubeSats built by NASA's

text: Ames Research Center

text: . These were named

text: Alexander

text: Graham

text: and

text: Bell

text: , after the

text: inventor of the telephone

text: . The purpose of these three satellites was to demonstrate the use of

text: smartphone

text: s as

text: avionics

text: in CubeSats. They each had a mass of  and were powered by lithium batteries. The fourth nanosat was a 3U CubeSat, called Dove-1, built by Cosmogia Inc. It carried a "technology development Earth imagery experiment" using the Earth's magnetic field for attitude control.

text: Motion controllers using accelerometers are used as controllers for video games, which was publicly introduced in 1981 by Datasoft's "Le Stick" controller for the Atari 2600, and made more popular since 2006 by the Wii Remote controller for Nintendo's Wii console, which uses accelerometers to detect its approximate orientation and acceleration, and serves an image sensor, so it can be used as a pointing device. It was followed by other similar devices, including the ASUS Eee Stick, Sony PlayStation Move (which also uses magnetometers to track the Earth's magnetic field and computer vision via the PlayStation Eye to aid in position tracking), and HP Swing. Other systems use different mechanisms for input, such as Microsoft's Kinect, which combines infrared structured light and computer vision, and the Razer Hydra, which uses a magnetic field to determine position and orientation.

text: Motion controllers using

text: accelerometer

text: s are used as controllers for

text: video game

text: s, which was publicly introduced in 1981 by

text: Datasoft

text: 's "Le Stick" controller for the

text: Atari 2600

text: , and made more popular since 2006 by the

text: Wii Remote

text: controller for Nintendo's

text: Wii

text: console, which uses accelerometers to detect its approximate orientation and acceleration, and serves an image sensor, so it can be used as a pointing device. It was followed by other similar devices, including the

text: ASUS Eee Stick

text: Sony

text: PlayStation Move

text: (which also uses

text: magnetometer

text: s to track the Earth's magnetic field and

text: computer vision

text: via the

text: PlayStation Eye

text: to aid in position tracking), and

text: HP

text: Swing. Other systems use different mechanisms for input, such as Microsoft's

text: Kinect

text: , which combines

text: infrared

text: structured light

text: and computer vision, and the

text: Razer Hydra

text: , which uses a magnetic field to determine position and orientation.

text: When a shark swims through the Earth's magnetic field, electromagnetic induction – phenomena which generates an electric field as charged particles move through a magnetic field – creates an electric field around the shark. Minute differences in the Earth's magnetic field at different locations result in minute differences in the induced electric field which may be detected by the shark's sensitive electroreceptors, especially as the head region moves back and forth during swimming (Lohmann and Johnsen 2000).

text: Researchers found out that very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds to navigate using the Earth's magnetic field. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds, according to the new study published in the 8 May 2014 edition of the journal Nature. Instead, the culprits consist of frequencies between 2 kHz and 5 MHz, such as AM radio signals and ordinary electronic equipment that might be found in businesses or private homes.

text: Single domain, in magnetism, refers to the state of a ferromagnet in which the magnetization does not vary across the magnet. A magnetic particle that stays in a single domain state for all magnetic fields is called a single domain particle (but other definitions are possible; see below). Such particles are very small (generally below a micrometre in diameter). They are also very important in a lot of applications because they have a high coercivity. They are the main source of hardness in hard magnets, the carriers of magnetic storage in tape drives, and the best recorders of the ancient Earth's magnetic field (see paleomagnetism).

text: Single domain, in

text: magnetism

text: , refers to the state of a

text: ferromagnet

text: in which the

text: magnetization

text: does not vary across the magnet. A magnetic particle that stays in a single domain state for all magnetic fields is called a single domain particle (but other definitions are possible; see below). Such particles are very small (generally below a

text: micrometre

text: in diameter). They are also very important in a lot of applications because they have a high

text: coercivity

text: . They are the main source of hardness in

text: hard magnet

text: s, the carriers of

text: magnetic storage

text: in

text: tape drives

text: , and the best recorders of the ancient

text: Earth's magnetic field

text: (see

text: paleomagnetism

text: In the Earth's magnetic field, NMR frequencies are in the audio frequency range, or the very low frequency and ultra low frequency bands of the radio frequency spectrum. Earth's field NMR (EFNMR) is typically stimulated by applying a relatively strong dc magnetic field pulse to the sample and, after the end of the pulse, analyzing the resulting low frequency alternating magnetic field that occurs in the Earth's magnetic field due to free induction decay (FID). These effects are exploited in some types of magnetometers, EFNMR spectrometers, and MRI imagers. Their inexpensive portable nature makes these instruments valuable for field use and for teaching the principles of NMR and MRI.

text: In the

text: Earth's magnetic field

text: , NMR frequencies are in the

text: audio frequency

text: range, or the

text: very low frequency

text: and

text: ultra low frequency

text: bands of the

text: radio frequency

text: spectrum. Earth's field NMR (EFNMR) is typically stimulated by applying a relatively strong dc magnetic field pulse to the sample and, after the end of the pulse, analyzing the resulting low frequency alternating magnetic field that occurs in the Earth's magnetic field due to

text: free induction decay

text: (FID). These effects are exploited in some types of

text: magnetometer

text: s, EFNMR spectrometers, and MRI imagers. Their inexpensive portable nature makes these instruments valuable for field use and for teaching the principles of NMR and MRI.

text: Earth's magnetic field is not constant—the strength of the field and the location of its poles vary. Moreover, the poles periodically reverse their orientation in a process called geomagnetic reversal. The most recent reversal occurred 780,000 years ago.

text: Earth's magnetic field is not constant—the strength of the field and the location of its poles vary. Moreover, the poles periodically reverse their orientation in a process called

text: geomagnetic reversal

text: . The

text: most recent reversal

text: occurred 780,000 years ago.

text: The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting fluids. The Earth's field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid inner core, with a radius of 1220 km, and a liquid outer core. The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about , to the core-mantle boundary, which is about . The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core.

text: The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically

text: conducting

text: fluids. The Earth's field originates in its core. This is a region of iron alloys extending to about 3400 km (the radius of the Earth is 6370 km). It is divided into a solid

text: inner core

text: , with a radius of 1220 km, and a liquid

text: outer core

text: . The motion of the liquid in the outer core is driven by heat flow from the inner core, which is about , to the

text: core-mantle boundary

text: , which is about . The pattern of flow is organized by the rotation of the Earth and the presence of the solid inner core.

text: The spiraling of electrons in a cylindrical vacuum chamber within a transverse magnetic field is also employed in the magnetron, a device for producing high frequency radio waves (microwaves). The synchrotron moves the particles through a path of constant radius, allowing it to be made as a pipe and so of much larger radius than is practical with the cyclotron and synchrocyclotron. The larger radius allows the use of numerous magnets, each of which imparts angular momentum and so allows particles of higher velocity (mass) to be kept within the bounds of the evacuated pipe. The magnetic field strength of each of the bending magnets is increased as the particles gain energy in order to keep the bending angle constant.

text: The spiraling of electrons in a cylindrical vacuum chamber within a transverse magnetic field is also employed in the

text: magnetron

text: , a device for producing high frequency radio waves (

text: microwaves

text: ). The

text: synchrotron

text: moves the particles through a path of constant radius, allowing it to be made as a pipe and so of much larger radius than is practical with the cyclotron and

text: synchrocyclotron

text: . The larger radius allows the use of numerous magnets, each of which imparts angular momentum and so allows particles of higher velocity (mass) to be kept within the bounds of the evacuated pipe. The magnetic field strength of each of the bending magnets is increased as the particles gain energy in order to keep the bending angle constant.

text: As a first-order approximation, the Earth's magnetic field can be modelled as a simple dipole (like a bar magnet), tilted about 10° with respect to the Earth's rotation axis (which defines the Geographic North and Geographic South Poles) and centred at the Earth's centre. The North and South Geomagnetic Poles are the antipodal points where the axis of this theoretical dipole intersects the Earth's surface. If the Earth's magnetic field were a perfect dipole then the field lines would be vertical at the Geomagnetic Poles, and they would coincide with the Magnetic Poles. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.

text: As a

text: first-order approximation

text: , the Earth's magnetic field can be modelled as a simple

text: dipole

text: (like a bar magnet), tilted about 10° with respect to the

text: Earth's rotation

text: axis (which defines the Geographic North and Geographic South Poles) and centred at the Earth's centre. The North and South Geomagnetic Poles are the

text: antipodal

text: points where the axis of this theoretical dipole intersects the Earth's surface. If the Earth's magnetic field were a perfect dipole then the

text: field line

text: s would be vertical at the Geomagnetic Poles, and they would coincide with the Magnetic Poles. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.

text: In 1831 Gauss developed a fruitful collaboration with the physics professor Wilhelm Weber, leading to new knowledge in magnetism (including finding a representation for the unit of magnetism in terms of mass, charge, and time) and the discovery of Kirchhoff's circuit laws in electricity. It was during this time that he formulated his namesake law. They constructed the first electromechanical telegraph in 1833, which connected the observatory with the institute for physics in Göttingen. Gauss ordered a magnetic observatory to be built in the garden of the observatory, and with Weber founded the "Magnetischer Verein" (magnetic club in German), which supported measurements of Earth's magnetic field in many regions of the world. He developed a method of measuring the horizontal intensity of the magnetic field which was in use well into the second half of the 20th century, and worked out the mathematical theory for separating the inner and outer (magnetospheric) sources of Earth's magnetic field.

text: In 1831 Gauss developed a fruitful collaboration with the physics professor

text: Wilhelm Weber

text: , leading to new knowledge in

text: magnetism

text: (including finding a representation for the unit of magnetism in terms of mass, charge, and time) and the discovery of

text: Kirchhoff's circuit laws

text: in electricity. It was during this time that he formulated his namesake

text: law

text: . They constructed the first

text: electromechanical telegraph

text: in 1833, which connected the observatory with the institute for physics in Göttingen. Gauss ordered a magnetic

text: observatory

text: to be built in the garden of the observatory, and with Weber founded the "Magnetischer Verein" (magnetic club in

text: German

text: ), which supported measurements of Earth's magnetic field in many regions of the world. He developed a method of measuring the horizontal intensity of the magnetic field which was in use well into the second half of the 20th century, and worked out the mathematical theory for separating the inner and outer (

text: magnetospheric

text: ) sources of Earth's magnetic field.

text: The Earth is constantly immersed in the solar wind, a rarefied flow of hot plasma (a gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree temperature of the Sun's outermost layer, the corona. The solar wind reaches Earth with a velocity typically around 400 km/s, a density of around 5 ions/cm and a magnetic field intensity of around 2–5 nT (for comparison, Earth's surface field is typically 30,000–50,000 nT). During magnetic storms, in particular, flows can be several times faster; the interplanetary magnetic field (IMF) may also be much stronger. Joan Feynman deduced in the 1970s that the long-term averages of solar wind speed correlated with geomagnetic activity.  Her work resulted from data collected by the Explorer 33 spacecraft.The solar wind and magnetosphere consist of plasma (ionized gas), which conducts electricity. It is well known (since Michael Faraday's work around 1830) that when an electrical conductor is placed within a magnetic field while relative motion occurs in a direction that the conductor cuts across (or is cut by), rather than along, the lines of the magnetic field, an electric current is induced within the conductor. The strength of the current depends on a) the rate of relative motion, b) the strength of the magnetic field, c) the number of conductors ganged together and d) the distance between the conductor and the magnetic field, while the direction of flow is dependent upon the direction of relative motion. Dynamos make use of this basic process ("the dynamo effect"), any and all conductors, solid or otherwise are so affected, including plasmas and other fluids.The IMF originates on the Sun, linked to the sunspots, and its field lines (lines of force) are dragged out by the solar wind. That alone would tend to line them up in the Sun-Earth direction, but the rotation of the Sun angles them at Earth by about 45 degrees forming a spiral in the ecliptic plane), known as the Parker spiral. The field lines passing Earth are therefore usually linked to those near the western edge ("limb") of the visible Sun at any time.The solar wind and the magnetosphere, being two electrically conducting fluids in relative motion, should be able in principle to generate electric currents by dynamo action and impart energy from the flow of the solar wind. However, this process is hampered by the fact that plasmas conduct readily along magnetic field lines, but less readily perpendicular to them. Energy is more effectively transferred by temporary magnetic connection between the field lines of the solar wind and those of the magnetosphere. Unsurprisingly this process is known as magnetic reconnection. As already mentioned, it happens most readily when the interplanetary field is directed southward, in a similar direction to the geomagnetic field in the inner regions of both the north magnetic pole and south magnetic pole.

text: The Earth is constantly immersed in the

text: solar wind

text: , a rarefied flow of hot plasma (a gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree temperature of the Sun's outermost layer, the

text: corona

text: . The solar wind reaches Earth with a velocity typically around 400 km/s, a density of around 5 ions/cm and a magnetic field intensity of around 2–5 nT (for comparison, Earth's surface field is typically 30,000–50,000 nT). During

text: magnetic storms

text: , in particular, flows can be several times faster; the

text: interplanetary magnetic field

text: (IMF) may also be much stronger. Joan Feynman deduced in the 1970s that the long-term averages of solar wind speed correlated with geomagnetic activity.  Her work resulted from data collected by the

text: Explorer 33

text: spacecraft.The solar wind and magnetosphere consist of

text: plasma

text: (ionized gas), which conducts electricity. It is well known (since

text: Michael Faraday

text: 's work around 1830) that when an electrical conductor is placed within a magnetic field while relative motion occurs in a direction that the conductor cuts across (or is cut by), rather than along, the lines of the magnetic field, an electric current is induced within the conductor. The strength of the current depends on a) the rate of relative motion, b) the strength of the magnetic field, c) the number of conductors ganged together and d) the distance between the conductor and the magnetic field, while the direction of flow is dependent upon the direction of relative motion.

text: Dynamo

text: s make use of this basic process ("the

text: dynamo effect

text: "), any and all conductors, solid or otherwise are so affected, including plasmas and other fluids.The IMF originates on the Sun, linked to the

text: sunspot

text: s, and its

text: field lines (lines of force)

text: are dragged out by the solar wind. That alone would tend to line them up in the Sun-Earth direction, but the rotation of the Sun angles them at Earth by about 45 degrees forming a spiral in the ecliptic plane), known as the

text: Parker spiral

text: . The field lines passing Earth are therefore usually linked to those near the western edge ("limb") of the visible Sun at any time.The solar wind and the magnetosphere, being two electrically conducting fluids in relative motion, should be able in principle to generate electric currents by dynamo action and impart energy from the flow of the solar wind. However, this process is hampered by the fact that plasmas conduct readily along magnetic field lines, but less readily perpendicular to them. Energy is more effectively transferred by temporary magnetic connection between the field lines of the solar wind and those of the magnetosphere. Unsurprisingly this process is known as

text: magnetic reconnection

text: . As already mentioned, it happens most readily when the interplanetary field is directed southward, in a similar direction to the geomagnetic field in the inner regions of both the

text: north magnetic pole

text: and

text: south magnetic pole

text: The Vine-Matthews hypothesis correlates the symmetric magnetic patterns seen on the seafloor with geomagnetic field reversals. At mid-ocean ridges, new crust is created by the injection, extrusion, and solidification of magma. After the magma has cooled through the Curie point, ferromagnetism becomes possible and the magnetic minerals in the newly formed crust orient themselves with the current background geomagnetic field. Lithospheric creation at the ridge is considered continuous and symmetrical as the new crust pushes the old crust laterally and equally on either side of the ridge. Therefore, as geomagnetic reversal occur, the crust on either side of the ridge will contain a record of remnant magnetizations of normal or reversed magnetizations in comparison to the current geomagnetic field. The ridge crest is analogous to “twin-headed tape recorder”, recording the Earth’s magnetic history.The intensity of the remnant magnetization is greater than the induced magnetization. The shape of the magnetic anomaly is controlled by the combination of the orientation of its total magnetization, the summation of the induced magnetization and remnant magnetization. Consequently, the shape of the magnetic anomaly is controlled predominately by the primary remnant vector. Blocks of crust at high latitudes have magnetic vectors that dip steeply downward in a normal magnetic field. However, close to the magnetic south pole, the magnetic vectors dip steeply downward in a reversed magnetic field and inclined steeply upwards in a normal magnetic field. There are positive magnetic anomalies over normally magnetized blocks and negative anomalies over reversed blocks. Local anomalies with a short period also exist, but are considered to be correlated with bathymetry.  In low latitudes, the vectors are shallowly dipping and dipolar. This confuses the positive and negative anomalies. At the magnetic equator, the magnetic field is horizontal; negative anomalies are related to normally magnetized blocks and positive anomalies with reversed. The amplitude of the anomaly, magnetic field strength, and the magnitude of the remanence all decrease from the poles to the equator.The orientation of the ridge affects the anomaly shape and amplitude. The component of the vector that effects the anomaly is at a maximum when the ridge is east-west and the magnetic profile is north-south. The anomalies are most apparent at high magnetic latitudes, north-south trending ridges at all latitudes, and east-west trending ridges at the magnetic equator.

text: The Vine-Matthews hypothesis correlates the symmetric magnetic patterns seen on the seafloor with

text: geomagnetic field reversals

text: . At mid-ocean ridges, new crust is created by the injection, extrusion, and solidification of magma. After the magma has cooled through the

text: Curie point

text: , ferromagnetism becomes possible and the magnetic minerals in the newly formed crust orient themselves with the current background geomagnetic field. Lithospheric creation at the ridge is considered continuous and symmetrical as the new crust pushes the old crust laterally and equally on either side of the ridge. Therefore, as geomagnetic reversal occur, the crust on either side of the ridge will contain a record of remnant magnetizations of normal or reversed magnetizations in comparison to the current geomagnetic field. The ridge crest is analogous to “twin-headed tape recorder”, recording the Earth’s magnetic history.The intensity of the remnant magnetization is greater than the

text: induced magnetization

text: . The shape of the

text: magnetic anomaly

text: is controlled by the combination of the orientation of its total magnetization, the summation of the induced magnetization and remnant magnetization. Consequently, the shape of the magnetic anomaly is controlled predominately by the primary remnant vector. Blocks of crust at high latitudes have magnetic vectors that dip steeply downward in a normal magnetic field. However, close to the magnetic south pole, the magnetic vectors dip steeply downward in a reversed magnetic field and inclined steeply upwards in a normal magnetic field. There are positive magnetic anomalies over normally magnetized blocks and negative anomalies over reversed blocks. Local anomalies with a short period also exist, but are considered to be correlated with

text: bathymetry

text: .  In low latitudes, the vectors are shallowly dipping and dipolar. This confuses the positive and negative anomalies. At the magnetic equator, the magnetic field is horizontal; negative anomalies are related to normally magnetized blocks and positive anomalies with reversed. The amplitude of the anomaly, magnetic field strength, and the magnitude of the remanence all decrease from the poles to the equator.The orientation of the ridge affects the anomaly shape and amplitude. The component of the vector that effects the anomaly is at a maximum when the ridge is east-west and the magnetic profile is north-south. The anomalies are most apparent at high magnetic latitudes, north-south trending ridges at all latitudes, and east-west trending ridges at the magnetic equator.

text: As a first-order approximation, the Earth's magnetic field can be modelled as a simple dipole (like a bar magnet), tilted about 9.6° with respect to the Earth's rotation axis (which defines the Geographic North and Geographic South Poles) and centered at the Earth's center. The North and South Geomagnetic Poles are the antipodal points where the axis of this theoretical dipole intersects the Earth's surface. If the Earth's magnetic field were a perfect dipole then the field lines would be vertical at the Geomagnetic Poles, and they would coincide with the North and South magnetic poles. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.

text: As a

text: first-order approximation

text: , the

text: Earth's magnetic field

text: can be modelled as a simple

text: dipole

text: (like a bar magnet), tilted about 9.6° with respect to the

text: Earth's rotation

text: axis (which defines the

text: Geographic North

text: and

text: Geographic South Pole

text: s) and centered at the Earth's center. The North and South Geomagnetic Poles are the

text: antipodal point

text: s where the axis of this theoretical dipole intersects the Earth's surface. If the Earth's magnetic field were a perfect dipole then the

text: field line

text: s would be vertical at the Geomagnetic Poles, and they would coincide with the

text: North

text: and

text: South

text: magnetic poles. However, the approximation is imperfect, and so the Magnetic and Geomagnetic Poles lie some distance apart.

text: In outer space, the magnetopause flows along the boundary between the region around an astronomical object (called the "magnetosphere") and surrounding plasma, in which electric phenomena are dominated or organized by this magnetic field. Earth is surrounded by a magnetosphere, as are the magnetized planets Jupiter, Ganymede, Saturn, Uranus and Neptune. Mercury is magnetized, but too weakly to trap plasma. Mars has patchy surface magnetization. The magnetosphere is the location where the outward magnetic pressure of the Earth's magnetic field is counterbalanced by the solar wind, a plasma. Most of the solar particles are deflected to either side of the magnetopause. However, some particles become trapped within the Earth's magnetic field and form radiation belts. The Van Allen radiation belt is a torus of energetic charged particles (i.e. a plasma) around Earth, trapped by Earth's magnetic field.

text: In outer space, the

text: magnetopause

text: flows along the boundary between the region around an astronomical object (called the "

text: magnetosphere

text: ") and surrounding plasma, in which electric phenomena are dominated or organized by this magnetic field. Earth is surrounded by a magnetosphere, as are the magnetized planets Jupiter, Ganymede, Saturn, Uranus and Neptune. Mercury is magnetized, but too weakly to trap plasma. Mars has patchy surface magnetization. The magnetosphere is the location where the outward magnetic pressure of the Earth's magnetic field is counterbalanced by the

text: solar wind

text: , a plasma. Most of the solar particles are deflected to either side of the magnetopause. However, some particles become trapped within the Earth's magnetic field and form

text: radiation belts

text: . The

text: Van Allen radiation belt

text: is a torus of energetic charged particles (i.e. a plasma) around Earth, trapped by Earth's magnetic field.

text: Charles Dodge was a pivotal figure in the history of the center.  Dodge, originally from Iowa, had done a bachelor's degree at the University of Iowa and then earned his MA and doctorate (DMA) in Music Composition at Columbia University.  While at Columbia, Dodge was very active at the Columbia-Princeton Electronic Music Center.  In particular, Dodge was one of the leading innovators in the emerging field of computer music composition (as opposed to analog electronic composition, the norm in the field through the 1970s).  Dodge created some of the first meritorious works in the field of computer music, including Earth’s Magnetic Field (1970), which mapped magnetic field data to musical sounds, Speech Songs, a 1974 work that used analysis and resynthesis of human voices, and Any Resemblance is Purely Coincidental (1980), which combines live piano performance with a digitally-manipulated recording of Enrico Caruso singing the aria "Vesti la giubba".

text: Charles Dodge

text: was a pivotal figure in the history of the center.  Dodge, originally from

text: Iowa

text: , had done a bachelor's degree at the

text: University of Iowa

text: and then earned his MA and doctorate (DMA) in Music Composition at

text: Columbia University

text: .  While at Columbia, Dodge was very active at the

text: Columbia-Princeton Electronic Music Center

text: .  In particular, Dodge was one of the leading innovators in the emerging field of computer music composition (as opposed to analog electronic composition, the norm in the field through the 1970s).  Dodge created some of the first meritorious works in the field of computer music, including Earth’s Magnetic Field (1970), which mapped

text: magnetic field

text: data to musical sounds, Speech Songs, a 1974 work that used analysis and resynthesis of human voices, and Any Resemblance is Purely Coincidental (1980), which combines live piano performance with a digitally-manipulated recording of

text: Enrico Caruso

text: singing the aria "

text: Vesti la giubba

text: The solar magnetic field extends well beyond the Sun itself. The electrically conducting solar wind plasma carries the Sun's magnetic field into space, forming what is called the interplanetary magnetic field. In an approximation known as ideal magnetohydrodynamics, plasma particles only move along the magnetic field lines. As a result, the outward-flowing solar wind stretches the interplanetary magnetic field outward, forcing it into a roughly radial structure. For a simple dipolar solar magnetic field, with opposite hemispherical polarities on either side of the solar magnetic equator, a thin current sheet is formed in the solar wind. At great distances, the rotation of the Sun twists the dipolar magnetic field and corresponding current sheet into an Archimedean spiral structure called the Parker spiral. The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field. The Sun's dipole magnetic field of 50–400 μT (at the photosphere) reduces with the inverse-cube of the distance to about 0.1 nT at the distance of Earth. However, according to spacecraft observations the interplanetary field at Earth's location is around 5 nT, about a hundred times greater. The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the Sun.

text: The solar magnetic field extends well beyond the Sun itself. The electrically conducting solar wind plasma carries the Sun's magnetic field into space, forming what is called the

text: interplanetary magnetic field

text: . In an approximation known as ideal

text: magnetohydrodynamics

text: , plasma particles only move along the magnetic field lines. As a result, the outward-flowing solar wind stretches the interplanetary magnetic field outward, forcing it into a roughly radial structure. For a simple dipolar solar magnetic field, with opposite hemispherical polarities on either side of the solar magnetic equator, a thin

text: current sheet

text: is formed in the solar wind. At great distances, the rotation of the Sun twists the dipolar magnetic field and corresponding current sheet into an

text: Archimedean spiral

text: structure called the

text: Parker spiral

text: . The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field. The Sun's dipole magnetic field of 50–400

text: μT

text: (at the photosphere) reduces with the inverse-cube of the distance to about 0.1 nT at the distance of Earth. However, according to spacecraft observations the interplanetary field at Earth's location is around 5 nT, about a hundred times greater. The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the Sun.

text: There is also evidence for magnetoreception in large mammals.  Resting and grazing cattle as well as roe deer (Capreolus capreolus) and red deer (Cervus elaphus) tend to align their body axes in the geomagnetic north-south direction.  Because wind, sunshine, and slope could be excluded as common ubiquitous factors in this study, alignment toward the vector of the magnetic field provided the most likely explanation for the observed behaviour. However, because of the descriptive nature of this study, alternative explanations (e.g., the sun compass) could not be excluded.  In a follow-up study, researchers analyzed body orientations of ruminants in localities where the geomagnetic field is disturbed by high-voltage power lines to determine how local variation in magnetic fields may affect orientation behaviour.  This was done by using satellite and aerial images of herds of cattle and field observations of grazing roe deer.  Body orientation of both species was random on pastures under or near power lines.  Moreover, cattle exposed to various magnetic fields directly beneath or in the vicinity of power lines trending in various magnetic directions exhibited distinct patterns of alignment.  The disturbing effect of the power lines on body alignment diminished with the distance from the conductors. In 2011 a group of Czech researchers, however, reported their failed attempt to replicate the finding using different Google Earth images.

text: There is also evidence for magnetoreception in large mammals.  Resting and grazing cattle as well as

text: roe deer

text: (Capreolus capreolus) and

text: red deer

text: Czech

text: researchers, however, reported their failed attempt to replicate the finding using different

text: Google Earth

text: images.

text: " describes the set of the Earth's magnetic field lines which cross the Earth's magnetic equator two earth radii from the center of the Earth.  L-shell parameters can also describe the magnetic fields of other planets.  In such cases, the parameter is renormalized for that planet's radius and magnetic field model.

text: " describes the set of the

text: Earth's magnetic field

text: lines which cross the Earth's magnetic equator two earth radii from the center of the Earth.  L-shell parameters can also describe the magnetic fields of other planets.  In such cases, the parameter is renormalized for that planet's radius and magnetic field model.

text: under the influence of the magnetic field of earth

text: The magnetic field is about 1.1% as strong as Earth's. At the Hermean equator, the relative strength of the magnetic field is around 300 nT, which is weaker than that of Jupiter's moon Ganymede. Mercury's magnetic field is weaker than Earth's because its core had cooled and solidified more quickly than Earth's. Although Mercury's magnetic field is much weaker than Earth's magnetic field, it is still strong enough to deflect the solar wind, inducing a magnetosphere. Because Mercury's magnetic field is weak while the interplanetary magnetic field it interacts with in its orbit is relatively strong, the solar wind dynamic pressure at Mercury′s orbit is also three times larger than at Earth.

text: The magnetic field is about 1.1% as strong as

text: Earth's

text: . At the Hermean equator, the relative strength of the magnetic field is around 300

text: nT

text: , which is weaker than that of

text: Jupiter

text: 's moon

text: Ganymede

text: . Mercury's magnetic field is weaker than Earth's because its core had cooled and solidified more quickly than Earth's. Although Mercury's magnetic field is much weaker than Earth's magnetic field, it is still strong enough to deflect the

text: solar wind

text: , inducing a

text: magnetosphere

text: . Because Mercury's magnetic field is weak while the

text: interplanetary magnetic field

text: it interacts with in its orbit is relatively strong, the solar wind dynamic pressure at Mercury′s orbit is also three times larger than at Earth.

text: Overhauser magnetometer provides extremely accurate measurements of the strength of the magnetic field. The Orsted (satellite) uses this type of magnetometer to map the magnetic fields over the surface of the earth.

text: Overhauser magnetometer

text: provides extremely accurate measurements of the strength of the

text: magnetic field

text: . The

text: Orsted (satellite)

text: uses this type of magnetometer to map the magnetic fields over the surface of the earth.

text: The nature of Earth's magnetic field is one of heteroscedastic fluctuation. An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength. It has gone up and down in the past for no apparent reason. Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases.

text: The nature of Earth's magnetic field is one of

text: heteroscedastic

text: fluctuation. An instantaneous measurement of it, or several measurements of it across the span of decades or centuries, are not sufficient to extrapolate an overall trend in the field strength. It has gone up and down in the past for no apparent reason. Also, noting the local intensity of the dipole field (or its fluctuation) is insufficient to characterize Earth's magnetic field as a whole, as it is not strictly a dipole field. The dipole component of Earth's field can diminish even while the total magnetic field remains the same or increases.

text: Space physics can be traced back to the ancient Chinese, who recorded sun spots. The Chinese also discovered the principle of the compass, but did not understand how it worked. During the 16th century, in De Magnete, William Gilbert gave the first description of the Earth's magnetic field, showing that the Earth itself is a great magnet, which explained why a compass needle points north. Deviations of the compass needle magnetic declination were recorded on navigation charts, and a detailed study of the declination near London by watchmaker George Graham resulted in the discovery of irregular magnetic fluctuations that we now call magnetic storms, so named by Alexander Von Humboldt. Gauss and William Weber made very careful measurements of Earth's magnetic field which showed systematic variations and random fluctuations. This suggested that the Earth was not an isolated body, but was influenced by external forces. A relationship between individual aurora and accompanying geomagnetic disturbances was noticed by Anders Celsius and Olof Peter Hiorter in 1747. In 1860, Elias Loomis (1811–1889) showed that the highest incidence of aurora is seen inside an oval of 20 - 25 degrees around the magnetic pole. In 1881, Hermann Fritz published a map of the "isochasms" or lines of constant magnetic field

text: Space physics can be traced back to the ancient Chinese, who recorded

text: sun spots

text: . The Chinese also discovered the principle of the

text: compass

text: , but did not understand how it worked. During the 16th century, in

text: De Magnete

text: William Gilbert

text: gave the first description of the Earth's magnetic field, showing that the Earth itself is a great magnet, which explained why a compass needle points north. Deviations of the compass needle

text: magnetic declination

text: were recorded on navigation charts, and a detailed study of the declination near London by watchmaker

text: George Graham

text: resulted in the discovery of irregular magnetic fluctuations that we now call magnetic storms, so named by

text: Alexander Von Humboldt

text: . Gauss and

text: William Weber

text: made very careful measurements of Earth's magnetic field which showed systematic variations and random fluctuations. This suggested that the Earth was not an isolated body, but was influenced by external forces. A relationship between individual aurora and accompanying geomagnetic disturbances was noticed by

text: Anders Celsius

text: and

text: Olof Peter Hiorter

text: in 1747. In 1860,

text: Elias Loomis

text: (1811–1889) showed that the highest incidence of aurora is seen inside an oval of 20 - 25 degrees around the magnetic pole. In 1881,

text: Hermann Fritz

text: published a map of the "isochasms" or lines of constant magnetic field

text: A magnetic core is a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies.  It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites.  The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a current-carrying coil of wire around the core.  The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core.

text: A magnetic core is a piece of

text: magnetic material

text: with a high

text: magnetic permeability

text: used to confine and guide

text: magnetic field

text: s in electrical,

text: electromechanical

text: and magnetic devices such as

text: electromagnet

text: s,

text: transformer

text: s,

text: electric motor

text: s,

text: generators

text: inductor

text: s, magnetic

text: recording head

text: s, and magnetic assemblies.  It is made of

text: ferromagnetic

text: metal such as iron, or

text: ferrimagnetic

text: compounds such as

text: ferrite

text: s.  The high permeability, relative to the surrounding air, causes the

text: magnetic field line

text: s to be concentrated in the core material. The magnetic field is often created by a current-carrying coil of wire around the core.  The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core.

text: Studies of loggerhead and leatherback hatchlings have shown that moonlight reflected from the sea is an important visual cuee  in guiding movement from the beach to the sea. This navigational mechanism becomes a handicap if nesting sites are affected by artificial lighting since this can mean that hatchlings head towards the artificial lights rather than offshore towards the moonlit sea. Hence, the use of moonlight by turtle hatchings as a navigational cue can be considered an 'evolutionary trap'. Loggerhead and green turtles can detect the orbital movement of waves and use this information to swim perpendicular to the waves crests. This means they swim offshore, since close to the shore, wave crests run parallel to the beach. Further offshore the Earth's magnetic field is used to maintain an offshore direction and therefore head towards the open sea The ability to head in a given direction without reference to landmarks, is called a compass mechanism and where magnetic cues are used to achieve this it is called a 'magnetic compass'.Hatchling loggerheads mature within the North Atlantic Gyre and it is important that they stay within this current system since here water temperatures are benign. It has been shown that loggerheads use the magnetic field to stay within the gyre. For example, when exposed to fields characteristic of a region at the edge of the gyre they responded by orienting in a direction which would keep them within the gyre. These responses are inherited rather than learned since the hatchlings tested were captured before reaching the ocean. Adult turtles may learn aspects of the magnetic field and use this to navigate in a learned rather than innate way.

text: Studies of loggerhead and leatherback hatchlings have shown that moonlight reflected from the sea is an important visual cuee  in guiding movement from the beach to the sea. This navigational mechanism becomes a handicap if nesting sites are affected by artificial lighting since this can mean that hatchlings head towards the artificial lights rather than offshore towards the moonlit sea. Hence, the use of moonlight by turtle hatchings as a navigational cue can be considered an '

text: evolutionary trap

text: '. Loggerhead and green turtles can detect the orbital movement of waves and use this information to swim perpendicular to the waves crests. This means they swim offshore, since close to the shore, wave crests run parallel to the beach. Further offshore the Earth's magnetic field is used to maintain an offshore direction and therefore head towards the open sea The ability to head in a given direction without reference to landmarks, is called a compass mechanism and where magnetic cues are used to achieve this it is called a 'magnetic compass'.Hatchling loggerheads mature within the

text: North Atlantic Gyre

text: and it is important that they stay within this current system since here water temperatures are benign. It has been shown that loggerheads use the magnetic field to stay within the gyre. For example, when exposed to fields characteristic of a region at the edge of the gyre they responded by orienting in a direction which would keep them within the gyre. These responses are inherited rather than learned since the hatchlings tested were captured before reaching the ocean. Adult turtles may learn aspects of the magnetic field and use this to navigate in a learned rather than innate way.

text: New measurements from the Cluster mission for the first time now can determine unambiguously the scale sizes of magnetic reconnection in the Earth's magnetosphere, both on the dayside magnetopause and in the magnetotail. Cluster is a four-spacecraft mission, with the four spacecraft in a tetrahedron arrangement, to separate spatial from temporal changes as the suite flies through space.  Cluster has now also unambiguously discovered 'reverse reconnection' near the polar cusps.  'Dayside reconnection' allows interconnection of the Earth's magnetic field with that of the Sun (the Interplanetary Magnetic Field), allowing particle and energy entry into the Earth's vicinity.  Tail reconnection allows release of energy stored in the Earth's magnetic tail, injecting particles deep into the magnetosphere, causing auroral substorms.  'Reverse reconnection' is reconnection of Earth's tail magnetic fields with northward Interplanetary Magnetic Fields, causing sunward convection in the Earth's ionosphere.  The Magnetospheric Multiscale Mission, launched on 13 March 2015, is improving on Cluster results by having a tighter constellation of spacecraft, allowing finer spatial measurements and finer time detail.   In this way the behavior of the electrical currents in the electron diffusion region will be better understood.

text: New measurements from the Cluster mission for the first time now can determine unambiguously the scale sizes of magnetic reconnection in the Earth's

text: magnetosphere

text: , both on the dayside

text: magnetopause

text: and in the

text: magnetotail

text: Cluster

text: is a four-spacecraft mission, with the four spacecraft in a tetrahedron arrangement, to separate spatial from temporal changes as the suite flies through space.  Cluster has now also unambiguously discovered 'reverse reconnection' near the polar cusps.  'Dayside reconnection' allows interconnection of the Earth's magnetic field with that of the Sun (the

text: Interplanetary Magnetic Field

text: ), allowing particle and energy entry into the Earth's vicinity.  Tail reconnection allows release of energy stored in the Earth's magnetic tail, injecting particles deep into the magnetosphere, causing auroral

text: substorm

text: s.  'Reverse reconnection' is reconnection of Earth's tail magnetic fields with northward Interplanetary Magnetic Fields, causing sunward convection in the Earth's

text: ionosphere

text: .  The

text: Magnetospheric Multiscale Mission

text: , launched on 13 March 2015, is improving on Cluster results by having a tighter constellation of spacecraft, allowing finer spatial measurements and finer time detail.   In this way the behavior of the electrical currents in the electron diffusion region will be better understood.

text: The galvanometer is oriented so that the plane of the coil is vertical and aligned along parallel to the horizontal component  of the Earth's magnetic field (i.e. parallel to the local "magnetic meridian"). When an electric current flows through the galvanometer coil, a second magnetic field  is created. At the center of the coil, where the compass needle is located, the coil's field is perpendicular to the plane of the coil. The magnitude of the coil's field is:

text: The primary objective of ACS is to attain a configuration favourable for communication to take place. Earth's magnetic field will be used for achieving this. Components of Passive ACS include permanent magnets and hysteresis rods. The hysteresis rods are soft magnetic materials which damp the angular oscillations of the satellite and the magnet aligns the antenna along  the earth's magnetic field.

text: Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth's interior out into space, where it meets the solar wind, a stream of charged particles emanating from the Sun. Its magnitude at the Earth's surface ranges from 25 to 65 microteslas (0.25 to 0.65 gauss). Roughly speaking it is the field of a magnetic dipole currently tilted at an angle of about 10 degrees with respect to Earth's rotational axis, as if there were a bar magnet placed at that angle at the center of the Earth. The North geomagnetic pole, located near Greenland in the northern hemisphere, is actually the south pole of the Earth's magnetic field, and the South geomagnetic pole is the north pole. Unlike a bar magnet, Earth's magnetic field changes over time because it is generated by a geodynamo (in Earth's case, the motion of molten iron alloys in its outer core).

text: Earth's magnetic field, also known as the geomagnetic field, is the

text: magnetic field

text: that extends from the

text: Earth

text: 's interior out into space, where it meets the

text: solar wind

text: , a stream of

text: charged particle

text: s emanating from the

text: Sun

text: . Its magnitude at the Earth's surface ranges from 25 to 65

text: microteslas

text: (0.25 to 0.65

text: gauss

text: ). Roughly speaking it is the field of a

text: magnetic dipole

text: currently tilted at an angle of about 10 degrees with respect to

text: Earth's rotational axis

text: , as if there were a

text: bar magnet

text: placed at that angle at the center of the Earth. The

text: North geomagnetic pole

text: , located near Greenland in the northern hemisphere, is actually the south pole of the Earth's magnetic field, and the

text: South geomagnetic pole

text: is the north pole. Unlike a bar magnet, Earth's magnetic field changes over time because it is generated by a

text: geodynamo

text: (in Earth's case, the motion of molten iron alloys in its

text: outer core

text: Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global, magnetic field. According to measurements taken by , it is about 1.1% the strength of Earth's. The magnetic-field strength at Mercury's equator is about . Like that of Earth, Mercury's magnetic field is dipolar. Unlike Earth, Mercury's poles are nearly aligned with the planet's spin axis. Measurements from both the  and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable.

text: Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global,

text: magnetic field

text: . According to measurements taken by , it is about 1.1% the strength of Earth's. The magnetic-field strength at Mercury's equator is about . Like that of Earth, Mercury's magnetic field is

text: dipolar

text: . Unlike Earth, Mercury's poles are nearly aligned with the planet's spin axis. Measurements from both the  and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable.

text: It was once believed that the dipole, which comprises much of the Earth's magnetic field and is misaligned along the rotation axis by 11.3 degrees, was caused by permanent magnetization of the materials in the earth. This means that dynamo theory was originally used to explain the Sun's magnetic field in its relationship with that of the Earth. However, this hypothesis, which was initially proposed by Joseph Larmor in 1919, has been modified due to extensive studies of magnetic secular variation, paleomagnetism (including polarity reversals), seismology, and the solar system's abundance of elements. Also, the application of the theories of Carl Friedrich Gauss to magnetic observations showed that Earth's magnetic field had an internal, rather than external, origin.

text: It was once believed that the

text: dipole

text: , which comprises much of the

text: Earth's magnetic field

text: and is misaligned along the rotation axis by 11.3 degrees, was caused by permanent magnetization of the materials in the earth. This means that dynamo theory was originally used to explain the Sun's magnetic field in its relationship with that of the Earth. However, this hypothesis, which was initially proposed by

text: Joseph Larmor

text: in 1919, has been modified due to extensive studies of magnetic secular variation,

text: paleomagnetism

text: (including

text: polarity reversal

text: s), seismology, and the solar system's abundance of elements. Also, the application of the theories of

text: Carl Friedrich Gauss

text: to magnetic observations showed that Earth's magnetic field had an internal, rather than external, origin.

text: Three decades later, when Earth's magnetic field was better understood, theories were advanced suggesting that the Earth's field might have reversed in the remote past. Most paleomagnetic research in the late 1950s included an examination of the wandering of the poles and continental drift. Although it was discovered that some rocks would reverse their magnetic field while cooling, it became apparent that most magnetized volcanic rocks preserved traces of the Earth's magnetic field at the time the rocks had cooled. In the absence of reliable methods for obtaining absolute ages for rocks, it was thought that reversals occurred approximately every million years.

text: Three decades later, when Earth's magnetic field was better understood, theories were advanced suggesting that the Earth's field might have reversed in the remote past. Most paleomagnetic research in the late 1950s included an examination of the wandering of the poles and

text: continental drift

text: . Although it was discovered that some rocks would reverse their magnetic field while cooling, it became apparent that most magnetized volcanic rocks preserved traces of the Earth's magnetic field at the time the rocks had cooled. In the absence of reliable methods for obtaining absolute ages for rocks, it was thought that reversals occurred approximately every million years.

text: A magnetic resonance imaging instrument (MRI scanner), or "nuclear magnetic resonance (NMR) imaging" scanner as it was originally known, uses powerful magnets to polarize and excite hydrogen nuclei (i.e., single protons) of water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body. The MRI machine emits a radio frequency (RF) pulse at the resonant frequency of the hydrogen atoms on water molecules. Radio frequency antennas ("RF coils") send the pulse to the area of the body to be examined. The RF pulse is absorbed by protons, causing their direction with respect to the primary magnetic field to change. When the RF pulse is turned off, the protons "relax" back to alignment with the primary magnet and emit radio-waves in the process. This radio-frequency emission from the hydrogen-atoms on water is what is detected and reconstructed into an image. The resonant frequency of a spinning magnetic dipole (of which protons are one example) is called the Larmor frequency and is determined by the strength of the main magnetic field and the chemical environment of the nuclei of interest. MRI uses three electromagnetic fields: a very strong (typically 1.5 to 3 teslas) static magnetic field to polarize the hydrogen nuclei, called the primary field; gradient fields that can be modified to vary in space and time (on the order of 1 kHz) for spatial encoding, often simply called gradients; and a spatially homogeneous radio-frequency (RF) field for manipulation of the hydrogen nuclei to produce measurable signals, collected through an RF antenna.

text: A magnetic resonance imaging instrument (

text: MRI scanner

text: ), or "nuclear magnetic resonance (

text: NMR

text: ) imaging" scanner as it was originally known, uses powerful magnets to polarize and excite

text: hydrogen

text: nuclei (i.e., single

text: proton

text: s) of water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body. The MRI machine emits a radio frequency (RF) pulse at the resonant frequency of the hydrogen atoms on water molecules. Radio frequency antennas ("RF coils") send the pulse to the area of the body to be examined. The RF pulse is absorbed by protons, causing their direction with respect to the primary magnetic field to change. When the RF pulse is turned off, the protons "relax" back to alignment with the primary magnet and emit radio-waves in the process. This radio-frequency emission from the hydrogen-atoms on water is what is detected and reconstructed into an image. The resonant frequency of a spinning magnetic dipole (of which protons are one example) is called the

text: Larmor frequency

text: and is determined by the strength of the main magnetic field and the chemical environment of the nuclei of interest. MRI uses three

text: electromagnetic field

text: s: a very strong (typically 1.5 to 3

text: teslas

text: ) static magnetic field to polarize the hydrogen nuclei, called the primary field; gradient fields that can be modified to vary in space and time (on the order of 1 kHz) for spatial encoding, often simply called gradients; and a spatially homogeneous

text: radio-frequency

text: RF

text: ) field for manipulation of the hydrogen nuclei to produce measurable signals, collected through an

text: RF antenna

text: The study of past magnetic field of the Earth is known as paleomagnetism. The polarity of the Earth's magnetic field is recorded in igneous rocks, and reversals of the field are thus detectable as "stripes" centered on mid-ocean ridges where the sea floor is spreading, while the stability of the geomagnetic poles between reversals has allowed paleomagnetists to track the past motion of continents. Reversals also provide the basis for magnetostratigraphy, a way of dating rocks and sediments. The field also magnetizes the crust, and magnetic anomalies can be used to search for deposits of metal ores.

text: The study of past magnetic field of the Earth is known as

text: paleomagnetism

text: . The polarity of the Earth's magnetic field is recorded in

text: igneous rock

text: s, and

text: reversals of the field

text: are thus detectable as "stripes" centered on

text: mid-ocean ridge

text: s where the

text: sea floor

text: is spreading, while the stability of the

text: geomagnetic pole

text: s between reversals has allowed paleomagnetists to track the past motion of continents. Reversals also provide the basis for

text: magnetostratigraphy

text: , a way of

text: dating

text: rocks and sediments. The field also magnetizes the crust, and

text: magnetic anomalies

text: can be used to search for deposits of metal

text: ores

text: The main focus of the SLIDE is in the levitation of the hoverboard. The levitation is achieved through the use of superconductors inside the board. Superconductors are conductors that have no internal resistance as long as they are kept below a certain temperature. When a metal has no internal resistance, that means with a current running through the metal, the current will run forever without a power source. When a superconductor is subjected to a magnetic field, essentially the superconductor aligns itself with the magnetic field and floats on top of it. The magnetic field in which the SLIDE will ride on has a magnetic pole of two south poles on the ends with a north pole in the middle. Generally with magnetic fields, the direction goes from north pole to south pole, so to simplify, the magnetic field created for the SLIDE pushes upwards in the middle and outwards equally split in both directions of the board keeping it levitating. The SLIDE maintains a hover height of about 1 to 2 inches above ground and can support about 440 pounds in weight. Superconductors only have their no internal resistance property when cooled to a certain temperature. In order to achieve this the SLIDE uses liquid nitrogen to cool it down to -197° Celsius. Even though liquid nitrogen cools down the superconductors of the SLIDE, it also boils at -197° Celsius. Because of this, it is difficult to have a constant supply of liquid nitrogen to continually cool down the superconductors, this is why the SLIDE can go for an average of 20 minutes on maximum liquid nitrogen capacity. Ross McGouran managed to get a maximum ride time of 30 minutes.

text: The main focus of the SLIDE is in the levitation of the hoverboard. The levitation is achieved through the use of

text: superconductors

text: inside the board. Superconductors are

text: conductors

text: that have no internal resistance as long as they are kept below a certain temperature. When a metal has no internal resistance, that means with a current running through the metal, the current will run forever without a power source. When a superconductor is subjected to a magnetic field, essentially the superconductor aligns itself with the magnetic field and floats on top of it. The magnetic field in which the SLIDE will ride on has a magnetic pole of two south poles on the ends with a north pole in the middle. Generally with magnetic fields, the direction goes from north pole to south pole, so to simplify, the magnetic field created for the SLIDE pushes upwards in the middle and outwards equally split in both directions of the board keeping it levitating. The SLIDE maintains a hover height of about 1 to 2 inches above ground and can support about 440 pounds in weight. Superconductors only have their no internal resistance property when cooled to a certain temperature. In order to achieve this the SLIDE uses

text: liquid nitrogen

text: to cool it down to -197° Celsius. Even though liquid nitrogen cools down the superconductors of the SLIDE, it also boils at -197° Celsius. Because of this, it is difficult to have a constant supply of liquid nitrogen to continually cool down the superconductors, this is why the SLIDE can go for an average of 20 minutes on maximum liquid nitrogen capacity. Ross McGouran managed to get a maximum ride time of 30 minutes.

text: The compass will indicate the magnetic field direction at the place where it happens to be at the time. If there are influences other than the Earth’s magnetic field, these may change the direction indicated by the compass. These effects are called deviation, and can be caused by a whole range of things. Any magnetic object or electrical current will have an influence, some more than others. The current in a dive computer is too small to affect the compass, even when quite near, but the hull of a ship or overhead power lines may make a difference even several meters away. It is difficult and often impossible to correct for all possible deviations, but it is worth checking a dive compass for deviation caused by dive equipment. It has been known for regulators to cause deviation, steel cylinders can cause deviation, and powerful lights may be a problem. A diver propulsion vehicle with an electric motor is also a potential problem for those who use them, though divers have been known to navogate adequately using compasses mounted on the handgrip of a DPV. A magnetic clip used to secure equipment to the diver's harness has a powerful magnet in both parts, and should not be used to hold the compass, as the part attached to the compass will produce a serious error.

text: The compass will indicate the magnetic field direction at the place where it happens to be at the time. If there are influences other than the

text: Earth’s magnetic field

text: , these may change the direction indicated by the compass. These effects are called

text: deviation

text: , and can be caused by a whole range of things. Any

text: magnetic

text: object or

text: electrical current

text: will have an influence, some more than others. The current in a

text: dive computer

text: is too small to affect the compass, even when quite near, but the hull of a ship or overhead power lines may make a difference even several meters away. It is difficult and often impossible to correct for all possible deviations, but it is worth checking a dive compass for deviation caused by dive equipment. It has been known for regulators to cause deviation,

text: steel

text: cylinders

text: can cause deviation, and powerful lights may be a problem. A

text: diver propulsion vehicle

text: with an

text: electric motor

text: is also a potential problem for those who use them, though divers have been known to navogate adequately using compasses mounted on the handgrip of a DPV. A magnetic clip used to secure equipment to the diver's harness has a powerful magnet in both parts, and should not be used to hold the compass, as the part attached to the compass will produce a serious error.

text: In zero field NMR all magnetic fields are shielded such that magnetic fields below 1 nT (nanotesla) are achieved and the nuclear precession frequencies of all nuclei are close to zero and indistinguishable. Under those circumstances the observed spectra are no-longer dictated by chemical shifts but primarily by J-coupling interactions which are independent of the external magnetic field. Since inductive detection schemes are not sensitive at very low frequencies, on the order of the J-couplings (typically between 0 and 1000 Hz), alternative detection schemes are used. Specifically, sensitive magnetometers turn out to be good detectors for zero field NMR. A zero magnetic field environment does not provide any polarization hence it is the combination of zero field NMR with hyperpolarization schemes that makes zero field NMR attractive.

text: In

text: zero field NMR

text: all magnetic fields are shielded such that magnetic fields below 1 nT (nano

text: tesla

text: ) are achieved and the nuclear precession frequencies of all nuclei are close to zero and indistinguishable. Under those circumstances the observed spectra are no-longer dictated by chemical shifts but primarily by J-coupling interactions which are independent of the external magnetic field. Since inductive detection schemes are not sensitive at very low frequencies, on the order of the J-couplings (typically between 0 and 1000 Hz), alternative detection schemes are used. Specifically, sensitive

text: magnetometer

text: s turn out to be good detectors for

text: zero field NMR

text: . A zero magnetic field environment does not provide any polarization hence it is the combination of zero field NMR with hyperpolarization schemes that makes zero field NMR attractive.

text: A study conducted in Panama demonstrated that Aphrissa statira loses its navigational capacity when exposed to a strong magnetic field, suggesting it uses the Earth's magnetic field to navigate.

text: A study conducted in

text: Panama

text: demonstrated that Aphrissa statira loses its navigational capacity when exposed to a strong magnetic field, suggesting it uses the

text: Earth's magnetic field

text: to navigate.

text: Tyson continues to note that despite losing some of his mental capacity, Faraday concluded that electricity and magnetism were connected by unseen fields, and postulated that light may also be tied to these forces. Using a sample of the optical glass that Davy had him make, Faraday discovered that an applied magnetic field could affect the polarization of light passing through the glass sample (a dielectric material), leading to what is called the Faraday effect and connecting these three forces. Faraday postulated that these fields existed across the planet, which would later by called Earth's magnetic field generated by the rotating molten iron inner core, as well as the phenomena that caused the planets to rotate around the sun. Faraday's work was initially rejected by the scientific community due to his lack of mathematical support, but James Clerk Maxwell would later come to rework Faraday's theories into the Maxwell's equations that validated Faraday's theories. Their combined efforts created the basis of science that drives the principles of modern communications today.

text: Tyson continues to note that despite losing some of his mental capacity, Faraday concluded that electricity and magnetism were connected by unseen fields, and postulated that light may also be tied to these forces. Using a sample of the optical glass that Davy had him make, Faraday discovered that an applied magnetic field could affect the

text: polarization

text: of light passing through the glass sample (a

text: dielectric material

text: ), leading to what is called the

text: Faraday effect

text: and connecting these three forces. Faraday postulated that these fields existed across the planet, which would later by called

text: Earth's magnetic field

text: generated by the rotating molten iron

text: inner core

text: , as well as the phenomena that caused the planets to rotate around the sun. Faraday's work was initially rejected by the scientific community due to his lack of mathematical support, but

text: James Clerk Maxwell

text: would later come to rework Faraday's theories into the

text: Maxwell's equations

text: that validated Faraday's theories. Their combined efforts created the basis of science that drives the principles of modern communications today.

text: In 1949, inspired by Bovis, a Czechoslovakian named Karel Drbal applied for a patent on a "Pharaoh's shaving device", a model pyramid alleged to maintain the sharpness of razor blades. According to the patent (#91,304), "The method of maintaining the razor blades and straight razor blades sharp by placing them in the magnetic field in such a way that the sharp edge lies in the direction of the magnetic lines." Drbal alleged that his device would focus "the earth's magnetic field", although he did not make it clear how this would work, or whether the device's shape or materials exerted the effect.

text: Under clear skies with the sun visible, both the birds with magnets and the birds without magnets had little trouble navigating back to the loft, yet at unfamiliar locations with overcast skies the birds with magnets glued to their backs were unable to successfully orient themselves and navigate back to the loft.  Keeton speculated that this was occurring because the birds without magnets were able to use the earth's magnetic fields to orient themselves in the correct direction, whereas the birds with magnets attached to their backs were unable to use the sun, familiar landmarks, or the earth's magnetic fields to find their way home. This discovery was extremely useful in explaining one of the most interesting questions of bird navigation.

text: The use of magnetic fields in flow measurement date back to 19th century, when in 1832 Michael Faraday attempted to determine the velocity of the River Thames. Faraday applied a method in which a flow (the river flow) is exposed to a magnetic field (earth magnetic field) and the induced voltage is measured using two electrodes across the same flow. This method is the basis of the one of the most successful commercial applications in flow metering known as the inductive flowmeter. The theory of such devices has been developed and comprehensively summarized by Prof. J. A. Shercliff in early 1950s. While inductive flowmeters are widely used for flow measurement in fluids at room temperatures such as beverages, chemicals and waste water, they are not suited for flow measurement of media such as hot, aggressive or for local measurements where surrounding obstacles limit access to the channel or pipe. Since they require electrodes to be inserted into the fluid, their use is limited to applications at temperatures far below the melting points of practically relevant metals.

text: The use of magnetic fields in flow measurement date back to 19th century, when in 1832

text: Michael Faraday

text: attempted to determine the velocity of the

text: River Thames

text: . Faraday applied a method in which a flow (the river flow) is exposed to a magnetic field (earth magnetic field) and the induced voltage is measured using two electrodes across the same flow. This method is the basis of the one of the most successful commercial applications in flow metering known as the inductive flowmeter. The theory of such devices has been developed and comprehensively summarized by Prof. J. A. Shercliff in early 1950s. While inductive flowmeters are widely used for flow measurement in fluids at room temperatures such as beverages, chemicals and waste water, they are not suited for flow measurement of media such as hot, aggressive or for local measurements where surrounding obstacles limit access to the channel or pipe. Since they require electrodes to be inserted into the fluid, their use is limited to applications at temperatures far below the melting points of practically relevant metals.

text: Earth's magnetic field results from its flowing liquid metallic core, according to the dynamo theory, but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles. Magnesium oxide, which is rocky on Earth, can be a liquid metal at the pressures and temperatures found in super-Earths and could generate a magnetic field in the mantles of super-Earths.

text: Earth's magnetic field results from its flowing liquid metallic core, according to the

text: dynamo theory

text: , but in super-Earths the mass can produce high pressures with large viscosities and high melting temperatures which could prevent the interiors from separating into different layers and so result in undifferentiated coreless mantles. Magnesium oxide, which is rocky on Earth, can be a liquid metal at the pressures and temperatures found in super-Earths and could generate a magnetic field in the mantles of super-Earths.

text: In physics, the dynamo theory proposes a mechanism by which a celestial body such as Earth or a star generates a magnetic field. The dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales.  A dynamo is thought to be the source of the Earth's magnetic field, as well as the magnetic fields of other planets.

text: In

text: physics

text: , the dynamo theory proposes a mechanism by which a celestial body such as

text: Earth

text: or a

text: star

text: generates a

text: magnetic field

text: . The dynamo theory describes the process through which a rotating,

text: convecting

text: , and

text: electric

text: ally conducting fluid can maintain a magnetic field over

text: astronomical

text: time scales.  A dynamo is thought to be the source of the

text: Earth's magnetic field

text: , as well as the magnetic fields of other planets.

text: In solid state physics in a non-zero temperature of the states of fine electronic structure determines the magnetic properties (single-ionic magnetic anisotropy, magnetic susceptibility as a function of temperature) and thermodynamic (Schottky-type specific heat, entropy etc.). The fine electronic structure calculations has been developed for the vast group of solid compounds containing transition metals and  rare earth elements [5] (group of 3d, 4d, 4f and 5f). In solid state physics, the fine electron structure is shaped by crystalline field whose effect is described using the multipolar operators defined in the convention, B. G. Wybourne'a or Stevens. Both conventions are consistent, providing a Crystal field parameters B, B and A. The fine electronic structure in the material containing paramagnetic ions determines single ionic anisotropy of material and has a basic knowledge about the behavior of atoms or ions in a solid material at low to medium temperatures.

text: The avian magnetic compass of the robin has been extensively researched and uses vision-based magnetoreception, in which the robin's ability to sense the magnetic field of the earth for navigation is affected by the light entering the bird's eye. The physical mechanism of the robin's magnetic sense is not fully understood, but may involve quantum entanglement of electron spins.

text: The avian magnetic compass of the robin has been extensively researched and uses vision-based

text: magnetoreception

text: , in which the robin's ability to sense the magnetic field of the earth for navigation is affected by the light entering the bird's eye. The physical mechanism of the robin's magnetic sense is not fully understood, but may involve

text: quantum entanglement

text: of electron spins.

text: The magnetic compass indicates the local direction of the ambient magnetic field, which is usually that of the Earth. This is usually a reliable and consistent feature and is very useful as a navigational aid as it is not affected by visibility, pressure, or the presence of water.

text: The

text: magnetic compass

text: indicates the local direction of the ambient

text: magnetic field

text: , which is usually that of the Earth. This is usually a reliable and consistent feature and is very useful as a navigational aid as it is not affected by visibility, pressure, or the presence of water.

text: Saturn has an intrinsic magnetic field that has a simple, symmetric shape – a magnetic dipole. Its strength at the equator – 0.2 gauss (20 µT) – is approximately one twentieth of that of the field around Jupiter and slightly weaker than Earth's magnetic field. As a result, Saturn's magnetosphere is much smaller than Jupiter's. When Voyager 2 entered the magnetosphere, the solar wind pressure was high and the magnetosphere extended only 19 Saturn radii, or 1.1 million km (712,000 mi), although it enlarged within several hours, and remained so for about three days. Most probably, the magnetic field is generated similarly to that of Jupiter – by currents in the liquid metallic-hydrogen layer called a metallic-hydrogen dynamo. This magnetosphere is efficient at deflecting the solar wind particles from the Sun. The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from the ionized particles in Titan's outer atmosphere. Saturn's magnetosphere, like Earth's, produces aurorae.

text: Saturn has an intrinsic

text: magnetic

text: field that has a simple, symmetric shape – a magnetic

text: dipole

text: . Its strength at the equator – 0.2

text: gauss

text: µT

text: ) – is approximately one twentieth of that of the field around Jupiter and slightly weaker than Earth's

text: magnetic field

text: . As a result, Saturn's

text: magnetosphere

text: is much smaller than Jupiter's. When Voyager 2 entered the magnetosphere, the

text: solar wind

text: pressure was high and the magnetosphere extended only 19 Saturn radii, or 1.1 million km (712,000 mi), although it enlarged within several hours, and remained so for about three days. Most probably, the magnetic field is generated similarly to that of Jupiter – by currents in the liquid metallic-hydrogen layer called a metallic-hydrogen dynamo. This magnetosphere is efficient at deflecting the

text: solar wind

text: particles from the

text: Sun

text: . The moon Titan orbits within the outer part of Saturn's magnetosphere and contributes plasma from the

text: ion

text: ized particles in Titan's outer atmosphere. Saturn's magnetosphere, like

text: Earth's

text: , produces

text: aurorae

text: Earth’s magnetic field: A number of moths use the Earth's magnetic field to navigate, as a study of the stray Heart and Dart suggests. Another study, this time of the migratory behaviour of the Silver Y, showed that this species, even at high altitudes, can correct its course with changing winds, and prefers flying with favourable winds, which suggests a great sense of direction. Aphrissa statira in Panama loses its navigational capacity when exposed to a magnetic field, suggesting it uses the Earth’s magnetic field.

text: Earth’s magnetic field: A number of moths use the

text: Earth's magnetic field

text: to navigate, as a study of the stray

text: Heart and Dart

text: suggests. Another study, this time of the migratory behaviour of the

text: Silver Y

text: , showed that this species, even at high altitudes, can correct its course with changing winds, and prefers flying with favourable winds, which suggests a great sense of direction.

text: Aphrissa statira

text: in

text: Panama

text: loses its navigational capacity when exposed to a magnetic field, suggesting it uses the Earth’s magnetic field.

text: The mollusc Tochuina tetraquetra (formerly Tritonia diomedea or Tritonia gigantea) has been studied for clues as to the neural mechanism behind magnetoreception in a species. Some of the earliest work with Tochuina showed that prior to a full moon Tochuina would orient their bodies between magnetic north and east. A Y-maze was established with a right turn equal to geomagnetic south and a left turn equal to geomagnetic east. Within this geomagnetic field 80% of Tochuina made a turn to the left or magnetic east. However, when a reversed magnetic field was applied that rotated magnetic north 180° there was no significant preference for either turn, which now corresponded with magnetic north and magnetic west. These results, though interesting, do not conclusively establish that Tochuina uses magnetic fields in magnetoreception. These experiments do not include a control for the activation of the Rubens’ coil in the reversed magnetic field experiments. Therefore, it is possible that heat or noise generated by the coil was responsible for the loss of choice preference.  Further work with Tochuina was unable to identify any neurons that showed rapid changes in firing as a result of magnetic fields. However, pedal 5 neurons, two bisymmetric neurons located within the Tochuina pedal ganglion, exhibited gradual changes in firing over time following 30 minutes of magnetic stimulation provided by a Rubens’ coil.  Further studies showed that pedal 7 neurons in the pedal ganglion were inhibited when exposed to magnetic fields over the course of 30 minutes. The function of both pedal 5 neurons and pedal 7 neurons is currently unknown.

text: The mollusc

text: Tochuina tetraquetra

text: The Earth has a magnetic field which is approximately aligned with its axis of rotation. A magnetic compass is a device that uses this field to determine the cardinal directions. Magnetic compasses are widely used, but only moderately accurate.

text: The

text: Earth

text: has a magnetic field which is approximately aligned with its axis of rotation. A

text: magnetic compass

text: is a device that uses this field to determine the cardinal directions. Magnetic compasses are widely used, but only moderately accurate.

text: Earth's magnetic field stops its atmosphere from being stripped away by the solar wind. Venus and Mars do not have magnetic fields, and as a result the solar wind is causing their atmospheres to gradually bleed away into space. Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into Earth's upper atmosphere, where its interactions create aurorae seen near the magnetic poles.

text: Earth's magnetic field

text: stops

text: its atmosphere

text: from being stripped away by the solar wind. Venus and Mars do not have magnetic fields, and as a result the solar wind is causing their atmospheres to gradually bleed away into space.

text: Coronal mass ejection

text: s and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into Earth's upper atmosphere, where its interactions create

text: aurorae

text: seen near the

text: magnetic poles

text: A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction.  When cooled below a temperature called the Curie temperature, the magnetization of a piece of ferromagnetic material spontaneously divides into many small regions called magnetic domains.  The magnetization within each domain points in a uniform direction, but the magnetization of different domains may point in different directions.   Magnetic domain structure is responsible for the magnetic behavior of ferromagnetic materials like iron, nickel, cobalt and their alloys, and  ferrimagnetic materials like ferrite.  This includes the formation of permanent magnets and the attraction of ferromagnetic materials to a magnetic field.    The regions separating magnetic domains are called domain walls, where the magnetization rotates coherently from the direction in one domain to that in the next domain.  The study of magnetic domains is called micromagnetics.

text: A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual

text: magnetic moment

text: s of the atoms are aligned with one another and they point in the same direction.  When cooled below a temperature called the

text: Curie temperature

text: , the magnetization of a piece of

text: ferromagnetic

text: material spontaneously divides into many small regions called magnetic domains.  The magnetization within each domain points in a uniform direction, but the magnetization of different domains may point in different directions.   Magnetic domain structure is responsible for the magnetic behavior of

text: ferromagnetic

text: materials like

text: iron

text: nickel

text: cobalt

text: and their

text: alloy

text: s, and

text: ferrimagnetic

text: materials like

text: ferrite

text: .  This includes the formation of

text: permanent magnet

text: s and the attraction of ferromagnetic materials to a magnetic field.    The regions separating magnetic domains are called

text: domain wall

text: s, where the magnetization rotates coherently from the direction in one domain to that in the next domain.  The study of magnetic domains is called

text: micromagnetics

text: Geomagnetic imprinting has not been proven to occur, but it appears to be plausible for several reasons.  The earth's magnetic field varies across the globe in such a way that different geographic areas have different magnetic fields associated with them.  Also, sea turtles have a well-developed magnetic sense  and can detect both the intensity (strength) of the Earth's field as well as the inclination angle (angle at which the field lines intersect the earth's surface).  Thus, it is plausible that sea turtles, and maybe salmon also, can recognize their home areas using the distinctive magnetic fields that exist there.

text: An astatic system comprises two equal and parallel magnetic needles, but with their polarities reversed. This arrangement protects the system from the influence of the terrestrial magnetic field, as the magnetisms of the two needles cancel each other out. Because of this phenomenon, astatic needles were often used in galvanometers.

text: An astatic system comprises two equal and parallel magnetic needles, but with their

text: polarities

text: reversed. This arrangement protects the system from the influence of the

text: terrestrial magnetic field

text: , as the

text: magnetisms

text: of the two needles cancel each other out. Because of this phenomenon, astatic needles were often used in

text: galvanometer

text: s.

text: Relatively shortly after his breakthrough Ugelstad gave a lecture in the United States. After the lecture some scientists asked if it was possible to magnetize the spheres, so they could be used to separate cells. The inquiry sparked new nights with research problems in John Ugelstad bedrooms and resulted in the development of magnetic monodisperse particles at SINTEF. The solution was designated as ingenious in its simplicity. Basically he made particles paramagnetic, i.e. they are only magnetic in a magnetic field. When this field is removed, the particles are non-magnetic.

text: The basic premise of the film, that the movement of the Earth's magnetic north and south poles to the middle latitude would cause a massive climatic shift, is only partially true. Although such an event (if it were possible) would result in dramatic effects on global weather patterns, it would not reverse the Earth's climate zones as shown in the film, since climate is governed not just by the Earth's magnetic field, but mainly by altitude and proximity to the poles via the tilt of the Earth's axis, which affords lower latitudes more direct sun rays.  Furthermore, the movement of the poles, not the magnetic poles, would move both arctic and temperate regions, but would not necessarily trigger an ice age.  It would not cause an ice age localized to Miami, as the film suggests.

text: The basic premise of the film, that the movement of the Earth's magnetic north and south poles to the middle latitude would cause a massive climatic shift, is only partially true. Although such an event (if it were possible) would result in dramatic effects on global weather patterns, it would not reverse the Earth's climate zones as shown in the film, since climate is governed not just by the Earth's magnetic field, but mainly by altitude and

text: proximity to the poles via the tilt of the Earth's axis

text: , which affords lower latitudes more direct sun rays.  Furthermore, the movement of the poles, not the magnetic poles, would move both arctic and temperate regions, but would not necessarily trigger an ice age.  It would not cause an ice age localized to Miami, as the film suggests.

text: One measuring device is placed at the surface of the sonde, the identical second of the pair is placed a necessary distance off the body of the sonde by unfolding a 1 m long boom (carbon composite tube). Two redundant pyrotechnical cutters cut one loop of thin rope to free the power of metal springs. The driven knee lever rotates the boom perpendicularly outwards and latches it in place. Only the use of a pair of sensors together with the rotation of the sonde allows to resolve the small natural magnetic field beneath the fields of the disturbing fields of the probe itself. The measurements to identify the fields produced by the craft took place on the route from Earth to Venus. The lack of magnetic cleanness was due to the reuse of the Mars Express spacecraft bus which did not carry a magnetometer. By combining the data from two-point simultaneous measurements and using software to identify and remove interference generated by Venus Express itself, it was possible to obtain results of a quality comparable to those produced by a magnetically clean craft.

text: One measuring device is placed at the surface of the sonde, the identical second of the pair is placed a necessary distance off the body of the sonde by unfolding a 1 m long boom (carbon composite tube). Two redundant pyrotechnical cutters cut one loop of thin rope to free the power of metal springs. The driven knee lever rotates the boom perpendicularly outwards and latches it in place. Only the use of a pair of sensors together with the rotation of the sonde allows to resolve the small natural magnetic field beneath the fields of the disturbing fields of the probe itself. The measurements to identify the fields produced by the craft took place on the route from Earth to Venus. The lack of magnetic cleanness was due to the reuse of the

text: Mars Express

text: spacecraft bus which did not carry a magnetometer. By combining the data from two-point simultaneous measurements and using software to identify and remove interference generated by Venus Express itself, it was possible to obtain results of a quality comparable to those produced by a magnetically clean craft.

text: Changing magnetic dipole fields (i.e., magnetic near-fields) are used commercially for many types of magnetic induction devices. These include motors and electrical transformers at low frequencies, and devices such as metal detectors and MRI scanner coils at higher frequencies. Sometimes these high-frequency magnetic fields change at radio frequencies without being far-field waves and thus radio waves; see RFID tags.See also near-field communication.Further uses of near-field EM effects commercially, may be found in the article on virtual photons, since at the quantum level, these fields are represented by these particles. Far-field effects (EMR) in the quantum picture of radiation, are represented by ordinary photons.

text: Changing magnetic dipole fields (i.e., magnetic near-fields) are used commercially for many types of

text: magnetic induction

text: devices. These include motors and electrical transformers at low frequencies, and devices such as

text: metal detector

text: s and

text: MRI

text: scanner coils at higher frequencies. Sometimes these high-frequency magnetic fields change at radio frequencies without being far-field waves and thus radio waves; see

text: RFID

text: tags.See also

text: near-field communication

text: .Further uses of near-field EM effects commercially, may be found in the article on

text: virtual photon

text: s, since at the quantum level, these fields are represented by these particles. Far-field effects (EMR) in the quantum picture of radiation, are represented by ordinary

text: photon

text: s.

text: Voyager's observations revealed that Uranus's magnetic field is peculiar, both because it does not originate from its geometric centre, and because it is tilted at 59° from the axis of rotation. In fact the magnetic dipole is shifted from the Uranus's centre towards the south rotational pole by as much as one third of the planetary radius. This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0.1 gauss (10 µT), whereas in the northern hemisphere it can be as high as 1.1 gauss (110 µT). The average field at the surface is 0.23 gauss (23 µT). In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator. The dipole moment of Uranus is 50 times that of Earth. Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants. One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean. Another possible explanation for the magnetosphere's alignment is that there are oceans of liquid diamond in Uranus's interior that would deter the magnetic field.

text: Voyager's observations revealed that Uranus's magnetic field is peculiar, both because it does not originate from its geometric centre, and because it is tilted at 59° from the axis of rotation. In fact the magnetic dipole is shifted from the Uranus's centre towards the south rotational pole by as much as one third of the planetary radius. This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0.1

text: gauss

text: µT

text: ), whereas in the northern hemisphere it can be as high as 1.1 gauss (110 µT). The average field at the surface is 0.23 gauss (23 µT). In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator. The dipole moment of Uranus is 50 times that of Earth. Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants. One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean. Another possible explanation for the magnetosphere's alignment is that there are oceans of liquid diamond in Uranus's interior that would deter the magnetic field.

text: The earliest use of these terms cited by the Oxford English Dictionary (OED) is by Walter M. Elsasser (1946) in the context of the generation of the Earth's magnetic field by currents in the core, with "toroidal" being parallel to lines of latitude and "poloidal" being in the direction of the magnetic field (i.e. towards the poles).

text: The earliest use of these terms cited by the Oxford English Dictionary (OED) is by

text: Walter M. Elsasser

text: (1946) in the context of the generation of the

text: Earth's magnetic field

text: by currents in the core, with "toroidal" being parallel to lines of latitude and "poloidal" being in the direction of the magnetic field (i.e. towards the poles).

text: If a planet's magnetic field is strong enough, its interaction with the solar wind forms a magnetosphere. Early space probes mapped out the gross dimensions of the Earth's magnetic field, which extends about 10 Earth radii towards the Sun. The solar wind, a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail, hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles called the Van Allen radiation belts.

text: If a planet's

text: magnetic field

text: is strong enough, its interaction with the solar wind forms a

text: magnetosphere

text: . Early

text: space probe

text: s mapped out the gross dimensions of the

text: Earth's magnetic field

text: , which extends about 10

text: Earth radii

text: towards the Sun. The solar wind, a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the

text: magnetic tail

text: , hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles called the

text: Van Allen radiation belt

text: s.

text: Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the magnetic declination does shift with time, this wandering is slow enough that a simple compass remains useful for navigation. Using magnetoception various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation.

text: Humans have used compasses for direction finding since the 11th century A.D. and for navigation since the 12th century. Although the

text: magnetic declination

text: does shift with time, this wandering is slow enough that a simple compass remains useful for navigation. Using

text: magnetoception

text: various other organisms, ranging from some types of bacteria to pigeons, use the Earth's magnetic field for orientation and navigation.

text: Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the solar wind. This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the interplanetary magnetic field (IMF).

text: Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the

text: solar wind

text: . This is a stream of charged particles leaving the Sun's

text: corona

text: and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the

text: interplanetary magnetic field

text: (IMF).

text: The importance of Earth's magnetic field to the development of complex life has been disputed. Kasting argues that the atmosphere provides sufficient protection against cosmic rays even during times of magnetic pole reversal and atmosphere loss by sputtering. Kasting also dismisses the role of the magnetic field in the evolution of eukaryotes citing the age of the oldest known magnetofossils.

text: The importance of Earth's magnetic field to the development of complex life has been disputed. Kasting argues that the atmosphere provides sufficient protection against cosmic rays even during times of magnetic pole reversal and atmosphere loss by sputtering. Kasting also dismisses the role of the magnetic field in the evolution of eukaryotes citing the age of the oldest known

text: magnetofossils

text: In early attempts to understand the Earth's magnetic field, measuring it was only part of the challenge. Understanding the measurements was also difficult because the mathematical and physical concepts had not yet been developed – in particular, the concept of a vector field that associates a vector with each point in space. The Earth's field is generally represented by field lines that run from pole to pole; the field at any point is parallel to a field line but does not have to point at either pole.  As late as the eighteenth century, however, a natural philosopher would believe that a magnet had to be pointing directly at something. Thus, the Earth's magnetic field had to be explained by localized sources, and as more was learned about the Earth's field, these sources became increasingly complex.

text: In early attempts to understand the Earth's magnetic field, measuring it was only part of the challenge. Understanding the measurements was also difficult because the mathematical and physical concepts had not yet been developed – in particular, the concept of a

text: vector field

text: that associates a vector with each point in space. The Earth's field is generally represented by

text: field line

text: s that run from pole to pole; the field at any point is parallel to a field line but does not have to point at either pole.  As late as the eighteenth century, however, a

text: natural philosopher

text: would believe that a magnet had to be pointing directly at something. Thus, the Earth's magnetic field had to be explained by localized sources, and as more was learned about the Earth's field, these sources became increasingly complex.

text: Depending on planet size and atmospheric composition, however, a lack of magnetic field does not determine the fate of a planet's atmosphere. Venus, for instance, has no powerful magnetic field. Its close proximity to the Sun also increases the speed and number of particles, and would presumably cause the atmosphere to be stripped almost entirely, much like that of Mars. Despite this, the atmosphere of Venus is  two orders of magnitudes denser than Earth's. Recent models indicate that stripping by solar wind accounts for less than 1/3 of total non-thermal loss processes.

text: Depending on planet size and atmospheric composition, however, a lack of magnetic field does not determine the fate of a planet's atmosphere.

text: Venus

text: , for instance, has no powerful magnetic field. Its close proximity to the

text: Sun

text: also increases the speed and number of particles, and would presumably cause the atmosphere to be stripped almost entirely, much like that of

text: Mars

text: . Despite this, the atmosphere of Venus is  two orders of magnitudes denser than Earth's. Recent models indicate that stripping by solar wind accounts for less than 1/3 of total non-thermal loss processes.

text: Collectively, strongly magnetic materials are often referred to as ferromagnets. However, this magnetism can arise as the result of more than one kind of magnetic order. In the strict sense, ferromagnetism refers to magnetic ordering where neighboring electron spins are aligned by the exchange interaction. The classic ferromagnet is iron. Below a critical temperature called the Curie temperature, ferromagnets have a spontaneous magnetization and there is hysteresis in their response to a changing magnetic field. Most importantly for rock magnetism, they have remanence, so they can record the Earth's field.

text: Collectively, strongly magnetic materials are often referred to as

text: ferromagnets

text: . However, this magnetism can arise as the result of more than one kind of magnetic order. In the strict sense,

text: ferromagnetism

text: refers to magnetic ordering where neighboring electron spins are aligned by the

text: exchange interaction

text: . The classic ferromagnet is

text: iron

text: . Below a critical temperature called the

text: Curie temperature

text: , ferromagnets have a

text: spontaneous magnetization

text: and there is

text: hysteresis

text: in their response to a changing magnetic field. Most importantly for rock magnetism, they have

text: remanence

text: , so they can record the Earth's field.

text: In experimental condensed matter physics, external magnetic fields act as thermodynamic variables that control the state, phase transitions and properties of material systems.  Nuclear magnetic resonance (NMR) is a technique by which external magnetic fields can be used to find resonance modes of individual electrons, thus giving information about the atomic, molecular and bond structure of their neighborhood. NMR experiments can be made in magnetic fields with strengths up to 60 Tesla.  Higher magnetic fields can improve the quality of NMR measurement data. Quantum oscillations is another experimental technique where high magnetic fields are used to study material properties such as the geometry of the Fermi surface.  High magnetic fields will be useful in experimentally testing of the various theoretical predictions such as the quantized magnetoelectric effect, image magnetic monopole, and the half-integer quantum Hall effect.

text: In experimental condensed matter physics, external

text: magnetic field

text: s act as

text: thermodynamic variable

text: s that control the state, phase transitions and properties of material systems.

text: Nuclear magnetic resonance

text: (NMR) is a technique by which external magnetic fields can be used to find resonance modes of individual electrons, thus giving information about the atomic, molecular and bond structure of their neighborhood. NMR experiments can be made in magnetic fields with strengths up to 60

text: Tesla

text: .  Higher magnetic fields can improve the quality of NMR measurement data.

entity_name: Quantum oscillations (experimental technique)

text: Quantum oscillations

text: is another experimental technique where high magnetic fields are used to study material properties such as the geometry of the

text: Fermi surface

text: .  High magnetic fields will be useful in experimentally testing of the various theoretical predictions such as the quantized

text: magnetoelectric effect

text: , image

text: magnetic monopole

text: , and the half-integer

text: quantum Hall effect

text: Earth's ring current is responsible for shielding the lower latitudes of the Earth from magnetospheric electric fields.  It therefore has a large effect on the electrodynamics of geomagnetic storms. The ring current system consists of a band, at a distance of 3 to 5 [[Earth radius|R, which lies in the equatorial plane and circulates clockwise around the Earth (when viewed from the north). The particles of this region produce a magnetic field in opposition to the Earth's magnetic field and so an Earthly observer would observe a decrease in the magnetic field in this area.

text: Earth

text: 's ring current is responsible for shielding the lower latitudes of the Earth from magnetospheric electric fields.  It therefore has a large effect on the electrodynamics of

text: geomagnetic storm

text: s. The ring current system consists of a band, at a distance of 3 to 5 [[Earth radius|R, which lies in the

text: equatorial plane

text: and circulates clockwise around the Earth (when viewed from the north). The particles of this region produce a magnetic field in opposition to the

text: Earth's magnetic field

text: and so an Earthly observer would observe a decrease in the

text: magnetic field

text: in this area.

text: Field Aligned Irregularities (FAIs) are anisotropic (different values when measured in different directions) perturbations of plasma density associated with magnetic fields. FAIs are often thought of in the context of the Earth's ionosphere where several natural processes generate FAIs in the E-region and F-region. They occur at 50 and 140 MHz, where electrons associated with the event become vertically aligned with Earth's magnetic field. FAI may occur for several hours after it starts. Optimum times for observance appear to be between 8 PM and midnight.

text: Field Aligned Irregularities (FAIs) are

text: anisotropic

text: (different values when measured in different directions) perturbations of

text: plasma

text: density associated with

text: magnetic field

text: s. FAIs are often thought of in the context of the Earth's

text: ionosphere

text: where several natural processes generate FAIs in the

text: E-region

text: and

text: F-region

text: . They occur at 50 and 140

text: MHz

text: , where

text: electrons

text: associated with the event become vertically aligned with Earth's

text: magnetic field

text: . FAI may occur for several hours after it starts. Optimum times for observance appear to be between 8 PM and midnight.

text: Walter M. Elsasser, considered a "father" of the presently accepted dynamo theory as an explanation of the Earth's magnetism, proposed that this magnetic field resulted from electric currents induced in the fluid outer core of the Earth. He revealed the history of the Earth's magnetic field through pioneering the study of the magnetic orientation of minerals in rocks.

text: Walter M. Elsasser

text: , considered a "father" of the presently accepted dynamo theory as an explanation of the Earth's magnetism, proposed that this magnetic field resulted from electric currents induced in the fluid outer core of the Earth. He revealed the history of the Earth's magnetic field through pioneering the study of the magnetic orientation of minerals in rocks.

text: Shannon makes magnetically levitated sculpture. The sculptures are suspended using permanent magnets. His series of suspended arrays includes room-filling three-dimensional crystalline arrangements of magnetic spheres each of which orient to Earth's magnetic field like a compass.

text: The Fishbowl tests were monitored by a large number of surface and aircraft-based stations in the wide area around the planned detonations and also in the region in the southern hemisphere in the Samoan Islands region, which was known in these tests as the southern conjugate region.  Johnston Island is in the northern hemisphere, as were all of the planned Operation Fishbowl nuclear detonation locations.  It was known from previous high altitude tests, as well as from theoretical work done in the late 1950s, that high-altitude nuclear tests produce a number of unique geophysical phenomena at the opposite end of the magnetic field line of the Earth's magnetic field.

text: The Fishbowl tests were monitored by a large number of surface and aircraft-based stations in the wide area around the planned detonations and also in the region in the southern hemisphere in the

text: Samoan Islands

text: region, which was known in these tests as the southern conjugate region.  Johnston Island is in the northern hemisphere, as were all of the planned Operation Fishbowl nuclear detonation locations.  It was known from previous high altitude tests, as well as from theoretical work done in the late 1950s, that high-altitude nuclear tests produce a number of unique geophysical phenomena at the opposite end of the magnetic field line of the

text: Earth's magnetic field

text: In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core.  A requirement for the induction of field is a rotating fluid.  Rotation in the outer core is supplied by the Coriolis effect caused by the rotation of the Earth.  The Coriolis force tends to organize fluid motions and electric currents into columns (also see Taylor columns) aligned with the rotation axis.  Induction or creation of magnetic field is described by the induction equation:

text: In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core.  A requirement for the induction of field is a rotating fluid.  Rotation in the outer core is supplied by the

text: Coriolis effect

text: caused by the rotation of the Earth.  The Coriolis force tends to organize fluid motions and electric currents into columns (also see

text: Taylor column

text: s) aligned with the rotation axis.  Induction or creation of magnetic field is described by the induction equation:

text: His primary scientific work—much inspired by earlier works of Robert Norman—was De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth) published in 1600. In this work, he describes many of his experiments with his model Earth called the terrella. From these experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses point north (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass).  He was the first to argue, correctly, that the centre of the Earth was iron, and he considered an important and related property of magnets was that they can be cut, each forming a new magnet with north and south poles.

text: His primary scientific work—much inspired by earlier works of

text: Robert Norman

text: —was

text: De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure

text: (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth) published in 1600. In this work, he describes many of his experiments with his model Earth called the

text: terrella

text: . From these experiments, he concluded that the

text: Earth

text: was itself

text: magnetic

text: and that this was the reason

text: compass

text: es point north (previously, some believed that it was the pole star (

text: Polaris

text: ) or a large magnetic island on the north pole that attracted the compass).  He was the first to argue, correctly, that the centre of the Earth was iron, and he considered an important and related property of magnets was that they can be cut, each forming a new magnet with north and south poles.

text: MRI requires a magnetic field that is both strong and uniform. The field strength of the magnet is measured in teslas – and while the majority of systems operate at 1.5 T, commercial systems are available between 0.2–7 T. Most clinical magnets are superconducting magnets, which require liquid helium. Lower field strengths can be achieved with permanent magnets, which are often used in "open" MRI scanners for claustrophobic patients. Recently, MRI has been demonstrated also at ultra-low fields, i.e., in the microtesla-to-millitesla range, where sufficient signal quality is made possible by prepolarization (on the order of 10-100 mT) and by measuring the Larmor precession fields at about 100 microtesla with highly sensitive superconducting quantum interference devices (SQUID

text: MRI requires a

text: magnetic field

text: that is both strong and

text: uniform

text: . The field strength of the magnet is measured in

text: teslas

text: – and while the majority of systems operate at 1.5 T, commercial systems are available between 0.2–7 T. Most clinical magnets are

text: superconducting

text: magnets, which require liquid

text: helium

text: . Lower field strengths can be achieved with permanent magnets, which are often used in "open" MRI scanners for

text: claustrophobic

text: patients. Recently, MRI has been demonstrated also at ultra-low fields, i.e., in the microtesla-to-millitesla range, where sufficient signal quality is made possible by prepolarization (on the order of 10-100 mT) and by measuring the Larmor precession fields at about 100 microtesla with highly sensitive superconducting quantum interference devices (

text: SQUID

text: Animals including birds and turtles can detect the Earth's magnetic field, and use the field to navigate during migration. Cows and wild deer tend to align their bodies north-south while relaxing, but not when the animals are under high-voltage power lines, leading researchers to believe magnetism is responsible.<ref name='Nature summary'></ref> In 2011, researchers reported their failed attempt to replicate the finding using different Google Earth images.

text: Animals including birds and turtles can detect the Earth's magnetic field, and use the field to navigate during

text: migration

text: . Cows and wild deer tend to align their bodies north-south while relaxing, but not when the animals are under high-voltage power lines, leading researchers to believe magnetism is responsible.<ref name='Nature summary'></ref> In 2011, researchers reported their failed attempt to replicate the finding using different

text: Google Earth

text: images.

text: According to the BBC, the "global map shows the variation in strength of the magnetic field after the Earth's dipole field has been removed (Earth's dipole field varies from 35,000 nano-Tesla (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to changes in the magnetic properties of the crustal rocks." The map is graphically represented by illustrating those landmarks of high magnetism in red to yellow hues and those of lower or negative magnetism in blue hues. It can pick up numerous aspects of the earth composition, including the sea floor spreading under the oceans, and reserve deposits like iron ore at Kursk. It identifies some prominent magnetic anomalies on the African continent. The dominant factors for magnetic anomalies picked up on the map are "the thickness of the magnetised layer and the composition of the crust". Younger crust is typically thinner, and naturally has a lower number of magnetic materials.

text: According to the BBC, the "global map shows the variation in strength of the magnetic field after the

text: Earth's dipole field

text: has been removed (Earth's dipole field varies from 35,000

text: nano-

text: Tesla

text: (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to changes in the magnetic properties of the crustal rocks." The map is graphically represented by illustrating those landmarks of high magnetism in red to yellow hues and those of lower or negative magnetism in blue hues. It can pick up numerous aspects of the earth composition, including the sea floor spreading under the oceans, and reserve deposits like iron ore at

text: Kursk

text: . It identifies some prominent magnetic anomalies on the African continent. The dominant factors for magnetic anomalies picked up on the map are "the thickness of the magnetised layer and the composition of the crust". Younger crust is typically thinner, and naturally has a lower number of magnetic materials.

text: The magnetocaloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic phenomenon in which a temperature change of a suitable material is caused by exposing the material to a changing magnetic field. This is also known by low temperature physicists as adiabatic demagnetization. In that part of the refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a magnetocaloric material to become disoriented from the magnetic field by the agitating action of the thermal energy (phonons) present in the material.  If the material is isolated so that no energy is allowed to (re)migrate into the material during this time, (i.e., an adiabatic process) the temperature drops as the domains absorb the thermal energy to perform their reorientation.  The randomization of the domains occurs in a similar fashion to the randomization at the curie temperature of a ferromagnetic material, except that magnetic dipoles overcome a decreasing external magnetic field while energy remains constant, instead of magnetic domains being disrupted from internal ferromagnetism as energy is added.

text: The magnetocaloric effect (MCE, from

text: magnet

text: and

text: calorie

text: ) is a magneto-

text: thermodynamic

text: phenomenon in which a temperature change of a suitable material is caused by exposing the material to a changing magnetic field. This is also known by low temperature physicists as

text: adiabatic

text: demagnetization. In that part of the refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a magnetocaloric material to become disoriented from the magnetic field by the agitating action of the thermal energy (

text: phonon

text: s) present in the material.  If the material is isolated so that no energy is allowed to (re)migrate into the material during this time, (i.e., an adiabatic process) the temperature drops as the domains absorb the thermal energy to perform their reorientation.  The randomization of the domains occurs in a similar fashion to the randomization at the

text: curie temperature

text: of a

text: ferromagnetic

text: material, except that

text: magnetic dipole

text: s overcome a decreasing external magnetic field while energy remains constant, instead of magnetic domains being disrupted from internal

text: ferromagnetism

text: as energy is added.

text: The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects the Earth's surface are called the North and South geomagnetic poles. If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them. However, the Earth's field has a significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either.

text: The global definition of the Earth's field is based on a mathematical model. If a line is drawn through the center of the Earth, parallel to the moment of the best-fitting magnetic dipole, the two positions where it intersects the Earth's surface are called the North and South

text: geomagnetic pole

text: s. If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them. However, the Earth's field has a significant

text: non-dipolar

text: contribution, so the poles do not coincide and compasses do not generally point at either.

text: As a result, the current can be directly calculated from the magnetic field knowing only the separation between the current and the magnetic field sensor. The details of this mathematical calculation can be found elsewhere, but what is important to know here is that this is a direct calculation that is not influenced by other materials or effects, and that through the use of Fast Fourier Transforms these calculations can be performed very quickly.  A magnetic field image can be converted to a current density image in about 1 or 2 seconds.

text: Otherwise, it is suggested that if the planet had a magnetic field, it would deflect the particles from the atmosphere (even the slow rotation of a tidally locked M-dwarf planet—it spins once for every time it orbits its star—would be enough to generate a magnetic field as long as part of the planet's interior remained molten). But actual mathematical models conclude that, even under the highest attainable dynamo-generated magnetic field strengths, exoplanets with masses like that of Earth lose a significant fraction of their atmospheres by the erosion of the exobase's atmosphere by CME bursts and XUV emissions (even those Earth-like planets closer than 0.8 AU—affecting also GK stars— probably lose their atmospheres).

text: Otherwise, it is suggested that if the planet had a magnetic field, it would deflect the particles from the atmosphere (even the slow rotation of a tidally locked M-dwarf planet—it spins once for every time it orbits its star—would be enough to generate a magnetic field as long as part of the planet's interior remained molten). But actual mathematical models conclude that, even under the highest attainable dynamo-generated magnetic field strengths, exoplanets with masses like that of Earth lose a significant fraction of their atmospheres by the erosion of the exobase's atmosphere by

text: CME

text: bursts and

text: XUV

text: emissions (even those Earth-like planets closer than 0.8 AU—affecting also GK stars— probably lose their atmospheres).

text: Although L-value is formally defined in terms of the Earth's true instantaneous magnetic field (or a high-order model like IGRF), it is often used to give a general picture of magnetic phenomena near the Earth, in which case it can be approximated using the dipole model of the Earth's magnetic field.

text: Although L-value is formally defined in terms of the Earth's true instantaneous magnetic field (or a high-order model like

text: IGRF

text: ), it is often used to give a general picture of magnetic phenomena near the Earth, in which case it can be approximated using the

entity_name: Dipole model of the Earth's magnetic field

text: dipole model of the Earth's magnetic field

text: Note that v does not represent the velocity that magnetic fields lines travel through the conductor. The magnetic field pattern observed depends on the frame of reference. They have no velocity on their own. To illustrate, imagine that one were to take a magnet and flip it 180 degrees. The result of assuming that these field lines actually have velocity of their own would be that magnetic field lines far away would swing to the other side, potentially faster than the speed of light, however, that is not what happens.

text: Archaeomagnetic dating is the study and interpretation of the signatures of the Earth's magnetic field at past times recorded in archaeological materials. These paleomagnetic signatures are fixed when ferromagnetic materials such as magnetite cool below the Curie point, freezing the magnetic moment of the material in the direction of the local magnetic field at that time. The direction and magnitude of the magnetic field of the Earth at a particular location varies with time, and can be used to constrain the age of materials. In conjunction with techniques such as radiometric dating, the technique can be used to construct and calibrate the geomagnetic polarity time scale.  This is one of the dating methodologies used for sites within the last 10,000 years. The method has been conceived by E. Thellier in the 1930's and the increased sensitivity of SQUID magnetometers has greatly promoted its use.

text: Archaeomagnetic dating is the study and interpretation of the signatures of the

text: Earth's magnetic field

text: at past times recorded in archaeological materials. These

text: paleomagnetic

text: signatures are fixed when

text: ferromagnetic

text: materials such as

text: magnetite

text: cool below the

text: Curie point

text: , freezing the magnetic moment of the material in the direction of the local magnetic field at that time. The direction and magnitude of the magnetic field of the Earth at a particular location

text: varies with time

text: , and can be used to constrain the age of materials. In conjunction with techniques such as

text: radiometric dating

text: , the technique can be used to construct and calibrate the

text: geomagnetic polarity time scale

text: .  This is one of the

text: dating methodologies

text: used for sites within the last 10,000 years. The method has been conceived by E. Thellier in the 1930's and the increased sensitivity of

text: SQUID

text: magnetometer

text: s has greatly promoted its use.

text: Magnetic camouflage in the form of "degaussing" coils has been used since the Second World War to protect ships from magnetic mines and other weapons with magnetic sensors. Horizontal coils around the whole or parts of the ship generate magnetic fields to "cancel out" distortions to the earth's magnetic field created by the ship.

text: Magnetic

text: camouflage in the form of "

text: degaussing

text: " coils has been used since the Second World War to protect ships from

text: magnetic mine

text: s and other weapons with magnetic sensors. Horizontal coils around the whole or parts of the ship generate

text: magnetic field

text: s to "cancel out" distortions to the earth's magnetic field created by the ship.

text: Magneto-harmonic systems need to bring the tags to magnetic saturation and thus create magnetic fields strong enough to be felt through a small magnet. They routinely interfere with CRT displays. Demagnetization-remagnetization units also create intense fields.

text: Another kind of laboratory remanence is anhysteretic remanence or anhysteretic remanent magnetization (ARM). This is induced by exposing a magnet to a large alternating field plus a small dc bias field. The amplitude of the alternating field is gradually reduced to zero to get an anhysteretic magnetization, and then the bias field is removed to get the remanence. The anhysteretic magnetization curve is often close to an average of the two branches of the hysteresis loop, and is assumed in some models to represent the lowest-energy state for a given field. ARM has also been studied because of its similarity to the write process in some magnetic recording technology and to the acquisition of natural remanent magnetization in rocks.

text: Another kind of laboratory remanence is anhysteretic remanence or anhysteretic remanent magnetization (ARM). This is induced by exposing a magnet to a large alternating field plus a small dc bias field. The amplitude of the alternating field is gradually reduced to zero to get an anhysteretic magnetization, and then the bias field is removed to get the remanence. The anhysteretic magnetization curve is often close to an average of the two branches of the

text: hysteresis loop

text: , and is assumed in some models to represent the lowest-energy state for a given field. ARM has also been studied because of its similarity to the write process in some magnetic recording technology and to the acquisition of

text: natural remanent magnetization

text: in rocks.

text: This process operates by moving particles in a magnetic field. The force experienced in the magnetic field is given by the equation f=m/k.H.dh/dx. with k=magnetic susceptibility, H-magnetic field strength, and dh/dx being the magnetic field gradient. As seen in this equation, the separation can be driven in two ways, either through a gradient in a magnetic field or the strength of a magnetic field. The different driving forces are used in the different concentrators. These can be either with water or without. Like the spirals, washwater aids in the separation of the particles while increases the entrainment of the gangue in the concentrate.

text: These experiments and expeditions led to several insights, one of which was an inference about the magnetic field of the sun. Like the Earth, the sun has a magnetic field. Initial estimates suggested that the sun's magnetic strength was about fifty times that of the Earth. The cosmic ray experiments indicated that the sun's magnetic strength was of the same magnitude as the Earth's; this result is now well-established by many subsequent measurements. The work on the magnetic field of the sun was featured in a 1949 article in Time magazine.

text: These experiments and expeditions led to several insights, one of which was an inference about the

text: magnetic field of the sun

text: . Like the Earth, the sun has a magnetic field. Initial estimates suggested that the sun's magnetic strength was about fifty times that of the Earth. The cosmic ray experiments indicated that the sun's magnetic strength was of the same magnitude as the Earth's; this result is now well-established by many subsequent measurements. The work on the magnetic field of the sun was featured in a 1949 article in Time magazine.

text: A steel core's remanence means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform. Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices.

text: A steel core's

text: remanence

text: means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high

text: inrush current

text: until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform. Overcurrent protection devices such as

text: fuses

text: must be selected to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced currents due to

text: geomagnetic disturbances

text: during

text: solar storms

text: can cause saturation of the core and operation of transformer protection devices.

text: When a direct current (DC) flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current. Careful design of the pole pieces ensures that the magnetic field is uniform, so that the angular deflection of the pointer is proportional to the current. A useful meter generally contains provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without oscillation.

text: When a

text: direct current

text: (DC) flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current. Careful design of the pole pieces ensures that the magnetic field is uniform, so that the angular deflection of the pointer is proportional to the current. A useful meter generally contains provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without

text: oscillation

text: Due to the weakening of the magnetic field, particularly during the transition period, greater amounts of radiation would be able to reach the Earth, increasing production of beryllium 10 and levels of carbon 14. However, it is likely that nothing serious would occur, as the human species has certainly lived through at least one such event; Homo erectus and possibly Homo heidelbergensis lived through the Matuyama reversal with no known ill effect, and excursions are shorter lived and do not result in permanent changes to the magnetic field. The major hazard to modern society is likely to be similar to those associated with geomagnetic storms, where satellites and power supplies may be damaged, although compass navigation would also be affected. Some forms of life which are thought to navigate based on magnetic fields may be disrupted, but again it is suggested that these species have survived excursions in the past.Since excursion periods are not always global, any effect might well only be experienced in certain places, with others relatively unaffected. The time period involved could be as little as a century, or as much as 10,000 years.

text: Due to the weakening of the magnetic field, particularly during the transition period, greater amounts of radiation would be able to reach the

text: Earth

text: , increasing production of

text: beryllium 10

text: and levels of

text: carbon 14

text: . However, it is likely that nothing serious would occur, as the human species has certainly lived through at least one such event;

text: Homo erectus

text: and possibly

text: Homo heidelbergensis

text: lived through the Matuyama reversal with no known ill effect, and excursions are shorter lived and do not result in permanent changes to the magnetic field. The major hazard to modern society is likely to be similar to those associated with

text: geomagnetic storm

text: s, where satellites and power supplies may be damaged, although compass navigation would also be affected. Some forms of life which are thought to navigate based on magnetic fields may be disrupted, but again it is suggested that these species have survived excursions in the past.Since excursion periods are not always global, any effect might well only be experienced in certain places, with others relatively unaffected. The time period involved could be as little as a century, or as much as 10,000 years.

text: Drosophila melanogaster is another invertebrate which may be able to orient to magnetic fields. Experimental techniques such as gene knockouts have allowed a closer examination of possible magnetoreception in these fruit flies. Various Drosophila strains have been trained to respond to magnetic fields. In a choice test flies were loaded into an apparatus with two arms that were surrounded by electric coils. Current was run through each of the coils, but only one was configured to produce a 5-Gauss magnetic field at a time. The flies in this T-maze were tested on their native ability to recognize the presence of the magnetic field in an arm and on their response following training where the magnetic field was paired with a sucrose reward. Many of the strains of flies showed a learned preference for the magnetic field following training. However, when the only cryptochrome found in Drosophila, type 1 Cry, is altered, either through a missense mutation or replacement of the Cry gene, the flies exhibit a loss of magnetosensitivity. Furthermore, when light is filtered to only allow wavelengths greater than 420 nm through, Drosophila loses its trained response to magnetic fields. This response to filtered light is likely linked to the action spectrum of fly-cryptochrome which has a range from 350 nm – 400 nm and plateaus from 430-450 nm.   Although researchers had believed that a tryptophan triad in cryptochrome was responsible for the free radicals on which magnetic fields could act, recent work with Drosophila has shown that tryptophan might not be behind cryptochrome dependent magnetoreception. Alteration of the tryptophan protein does not result in the loss of magnetosensitivity of a fly expressing either type 1 Cry or the cryptochrome found in vertebrates, type 2 Cry. Therefore, it remains unclear exactly how cryptochrome mediates magnetoreception. These experiments used a 5 gauss magnetic field, 10 times the strength of the Earth's magnetic field).  Drosophila has not been shown to be able to respond to the Earth’s weaker magnetic field.

text: Drosophila melanogaster

text: is another invertebrate which may be able to orient to magnetic fields. Experimental techniques such as gene knockouts have allowed a closer examination of possible magnetoreception in these fruit flies. Various Drosophila strains have been trained to respond to magnetic fields. In a

text: choice test

text: tryptophan

text: might not be behind cryptochrome dependent magnetoreception. Alteration of the tryptophan protein does not result in the loss of magnetosensitivity of a fly expressing either type 1 Cry or the cryptochrome found in vertebrates, type 2 Cry. Therefore, it remains unclear exactly how cryptochrome mediates magnetoreception. These experiments used a 5 gauss magnetic field, 10 times the strength of the

text: Earth's magnetic field

text: ).  Drosophila has not been shown to be able to respond to the Earth’s weaker magnetic field.

text: Several species of sharks have demonstrated the ability to sense magnetic fields (Kalmijn, 1978; Ryan, 1980; Klimley, 1993; 2002). The Ampullae of Lorenzini organ within sharks is used to detect weak electrical fields at short ranges. The detection range of this organ is effective only within inches, as sharks sense bioelectrical fields in the final stages of prey capture. The  flux per unit area of certain permanent magnets, particularly Neodymium-Iron-Boride and Barium-Ferrite magnets, corresponds closely with the detection range of the Ampullae of Lorenzini. The fields generated by these permanent magnets (ferrite and rare-earth types) decrease at the inverse cube of the distance from the magnet to sharks and rays. Therefore, at distances of a few meters from the magnet, the field exerted is less than the Earth's magnetic field. Animals which lack that Ampullae of Lorenzini organ do not display aversive behavior in close proximity to the magnetic field, making this technology selective.

text: Several species of sharks have demonstrated the ability to sense magnetic fields (Kalmijn, 1978; Ryan, 1980; Klimley, 1993; 2002). The Ampullae of Lorenzini organ within sharks is used to detect weak electrical fields at short ranges. The detection range of this organ is effective only within inches, as sharks sense bioelectrical fields in the final stages of prey capture. The  flux per unit area of certain permanent magnets, particularly Neodymium-Iron-Boride and Barium-Ferrite magnets, corresponds closely with the detection range of the

text: Ampullae of Lorenzini

text: . The fields generated by these permanent magnets (ferrite and rare-earth types) decrease at the inverse cube of the distance from the magnet to sharks and rays. Therefore, at distances of a few meters from the magnet, the field exerted is less than the Earth's magnetic field. Animals which lack that Ampullae of Lorenzini organ do not display aversive behavior in close proximity to the magnetic field, making this technology selective.

text: is simulation to verify the difference in the magnetic field when the EPM is ON and OFF. This simulation was made using finite element approach by the software COMSOL Multiphysics®.  The picture below shows a simulation of the Magnetic Flux density Field (B) for the EPM ON and OFF (with a calculation of the flux in that specific plane) and below shows multiple cross section measurements of the flux density on top of the EPM (ON and OFF as well). The simulations shown that there are at least 4 orders of magnitude of difference in the external magnetic fields between the two operation modes confirming the magnetic circuit model.

text: Dynamo theory suggests that convection in the outer core, combined with the Coriolis effect, gives rise to Earth's magnetic field. The solid inner core is too hot to hold a permanent magnetic field (see Curie temperature) but probably acts to stabilize the magnetic field generated by the liquid outer core. The average magnetic field strength in Earth's outer core is estimated to be 25 Gauss (2.5 mT), 50 times stronger than the magnetic field at the surface.

text: Dynamo theory

text: suggests that convection in the outer core, combined with the

text: Coriolis effect

text: , gives rise to

text: Earth's magnetic field

text: . The solid inner core is too hot to hold a permanent magnetic field (see

text: Curie temperature

text: ) but probably acts to stabilize the magnetic field generated by the liquid outer core. The average magnetic field strength in Earth's outer core is estimated to be 25 Gauss (2.5 mT), 50 times stronger than the magnetic field at the surface.

text: The atomic beam standard is a direct extension of the Stern-Gerlach atomic splitting experiment. The atoms of choice are heated in an oven to create gas, which is collimated into a beam.  This beam, consisting of a mixture of atoms in two states, passes through a state-selector magnet A, where atoms of the wrong state are separated out from the beam. The remaining beam is exposed to an RF field at or near the transition frequency.  The beam then passes through a space containing a static homogeneous magnetic field before it is again exposed to the RF field. The RF field and the C-field coil will flip the state of the atoms, with a probability depending on how close the microwave frequency is to the atomic transition frequency. After the second RF field exposure the atomic beam passes through a second state selector magnet B, where the atoms that did not change state (are still in the state selected by magnet A) are discarded.  This way, the number of atoms which survive magnet B is related to the microwaves' ability to match the atomic transition frequency.  After the second state selector, a mass-spectrometer using an ionizer detects the rate of atoms being received.

text: The atomic beam standard is a direct extension of the

text: Stern-Gerlach

text: Equipment sometimes requires isolation from external magnetic fields.  For static or slowly varying magnetic fields (below about 100 kHz) the Faraday shielding described above is ineffective.  In these cases shields made of high magnetic permeability metal alloys can be used, such as sheets of Permalloy and Mu-Metal, or with nanocrystalline grain structure ferromagnetic metal coatings.  These materials don't block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the magnetic field lines around the shielded volume.  The best shape for magnetic shields is thus a closed container surrounding the shielded volume.  The effectiveness of this type of shielding depends on the material's permeability, which generally drops off at both very low magnetic field strengths and at high field strengths where the material becomes saturated.  So to achieve low residual fields, magnetic shields often consist of several enclosures one inside the other, each of which successively reduces the field inside it.

text: Equipment sometimes requires isolation from external magnetic fields.  For static or slowly varying magnetic fields (below about 100 kHz) the Faraday shielding described above is ineffective.  In these cases shields made of high

text: magnetic permeability

text: metal

text: alloy

text: s can be used, such as sheets of

text: Permalloy

text: and

text: Mu-Metal

text: , or with nanocrystalline grain structure ferromagnetic metal coatings.  These materials don't block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the

text: magnetic field lines

text: around the shielded volume.  The best shape for magnetic shields is thus a closed container surrounding the shielded volume.  The effectiveness of this type of shielding depends on the material's permeability, which generally drops off at both very low magnetic field strengths and at high field strengths where the material becomes

text: saturated

text: .  So to achieve low residual fields, magnetic shields often consist of several enclosures one inside the other, each of which successively reduces the field inside it.

text: Anti-magnetic seal is sticker which is based on a special sealing duct tape. It is equipped with a sealed capsule, where there is the element sensitive to the magnetic field (suspension, rare earth metals). Microscopic particles contained in the suspension are sensitive to magnetic fields. They inform about the impact of magnet to the counter, that control energy consumption by changing its original state and spread inside the capsule or change the picture. The indicator seal is mounted by sticking to the count’s hull. An individual number provides protection against counterfeits. It is applied using a laser or printing method.

text: Anti-magnetic seal is sticker which is based on a special sealing duct tape. It is equipped with a sealed capsule, where there is the element sensitive to the magnetic field (

text: suspension

text: rare earth metals

text: ). Microscopic particles contained in the suspension are sensitive to magnetic fields. They inform about the impact of magnet to the counter, that control energy consumption by changing its original state and spread inside the capsule or change the picture. The indicator seal is mounted by sticking to the count’s hull. An individual number provides protection against counterfeits. It is applied using a

text: laser

text: or printing method.

text: A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earth's magnetic field. The increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth’s magnetic field and transfers an increased energy into the magnetosphere. Both interactions cause an increase in plasma movement through the magnetosphere (driven by increased electric fields inside the magnetosphere) and an increase in electric current in the magnetosphere and ionosphere.

text: A geomagnetic storm is a temporary disturbance of the

text: Earth

text: 's

text: magnetosphere

text: caused by a

text: solar wind

text: Earth's magnetic field

text: . The increase in the solar wind pressure initially compresses the magnetosphere. The solar wind's magnetic field interacts with the Earth’s magnetic field and transfers an increased energy into the magnetosphere. Both interactions cause an increase in plasma movement through the magnetosphere (driven by increased electric fields inside the magnetosphere) and an increase in electric current in the magnetosphere and

text: ionosphere

text: An early concept design for Magenta by George Pérez appeared in DC Sampler #2, with the character's initial name being Polara and her color scheme consisting of red and blue rather than magenta and white. Frankie Kane was a one time girlfriend of Wally West, who gained magnetic powers which killed her family. Not knowing her purpose in life, she became a villain and first joined the Cicada cult and the New Rogues before reforming. Magenta can generate and control magnetic fields, which she can use to move, lift, and manipulate ferrous metals. She can focus her powers into blasts of concussive magnetic force that can shatter steel, or fire electromagnetic pulses to disrupt electronic systems. She can concentrate her magnetic powers into a protective shield that repels metals and most physical assaults. By surrounding herself with an aura of magnetism that has an equal polarity to the Earth's own geomagnetic field, she can cause the Earth to repel her upward, and thereby fly by magnetic levitation.

text: An early concept design for Magenta by

text: George Pérez

text: appeared in DC Sampler #2, with the character's initial name being Polara and her color scheme consisting of

text: red

text: and

text: blue

text: rather than

text: magenta

text: and

text: white

text: . Frankie Kane was a one time girlfriend of

text: Wally West

text: , who gained magnetic powers which killed her family. Not knowing her purpose in life, she became a villain and first joined the

text: Cicada

text: cult and the New Rogues before reforming. Magenta can generate and control magnetic fields, which she can use to move, lift, and manipulate

text: ferrous

text: metals. She can focus her powers into blasts of concussive magnetic force that can shatter steel, or fire

text: electromagnetic pulse

text: s to disrupt electronic systems. She can concentrate her magnetic powers into a protective shield that repels metals and most physical assaults. By surrounding herself with an aura of

text: magnetism

text: that has an equal

text: polarity

text: to the Earth's own

text: geomagnetic

text: field, she can cause the Earth to repel her upward, and thereby fly by

text: magnetic levitation

text: Robert Norman is noted for The Newe Attractive, a pamphlet published in 1581 describing the lodestone (magnet) and practical aspects of navigation. More importantly, it included Norman's discovery of magnetic dip, the incline at an angle from the horizon by a compass needle. This effect is caused by the Earth's magnetic field not running parallel to the planet's surface.  Norman demonstrated magnetic dip by creating a compass needle that pivoted on a horizontal axis. The needle tilted at a steep angle relative to the horizon line.

text: Robert Norman is noted for The Newe Attractive, a pamphlet published in 1581 describing the

text: lodestone

text: magnet

text: ) and practical aspects of navigation. More importantly, it included Norman's discovery of

text: magnetic dip

text: , the incline at an angle from the horizon by a compass needle. This effect is caused by the

text: Earth's

text: magnetic field

text: not running parallel to the planet's surface.  Norman demonstrated magnetic dip by creating a compass needle that pivoted on a horizontal axis. The needle tilted at a steep angle relative to the

text: horizon

text: line.

text: The  square building contains a  diameter  3-axis Braunbek coil with four loops on each axis. The coil cancels the Earth's magnetic field within a central  spherical volume. Fluctuations in the ambient field are removed by a servo control, producing stability to half a nanotesla. An artificial magnetic vector can be produced and rotated at a variable rate.  Helmholtz coils are used for perm/deperm operations. A  monorail hoist is provided for equipment handling. HEPA filtration and air conditioning are provided.

text: The  square building contains a  diameter  3-axis Braunbek coil with four loops on each axis. The coil cancels the

text: Earth's magnetic field

text: within a central  spherical volume. Fluctuations in the ambient field are removed by a servo control, producing stability to half a

text: nanotesla

text: . An artificial magnetic vector can be produced and rotated at a variable rate.

text: Helmholtz coil

text: s are used for perm/

text: deperm

text: operations. A  monorail hoist is provided for equipment handling.

text: HEPA

text: filtration and air conditioning are provided.

text: The Earth's field is roughly like a tilted dipole, but it changes over time (a phenomenon called geomagnetic secular variation). Mostly the geomagnetic pole stays near the geographic pole, but at random intervals averaging 440,000 to a million years or so, the polarity of the Earth's field reverses. These geomagnetic reversals, analyzed within a Geomagnetic Polarity Time Scale, contain 184 polarity intervals in the last 83 million years, with change in frequency over time, with the most recent brief complete reversal of the Laschamp event occurring 41,000 years ago during the last glacial period. Geologists observed geomagnetic reversal recorded in volcanic rocks, through magnetostratigraphy correlation (see natural remanent magnetization) and their signature can be seen as parallel linear magnetic anomaly stripes on the seafloor. These stripes provide quantitative information on seafloor spreading, a part of plate tectonics. They are the basis of magnetostratigraphy, which correlates magnetic reversals with other stratigraphies to construct geologic time scales. In addition, the magnetization in rocks can be used to measure the motion of continents.

text: The Earth's field is roughly like a tilted

text: dipole

text: , but it changes over time (a phenomenon called

text: geomagnetic secular variation

text: ). Mostly the

text: geomagnetic pole

text: stays near the

text: geographic pole

text: , but at random intervals averaging 440,000 to a million years or so, the polarity of the Earth's field reverses. These

text: geomagnetic reversals

text: , analyzed within a

text: Geomagnetic Polarity Time Scale

text: , contain 184 polarity intervals in the last 83 million years, with change in frequency over time, with the most recent brief complete reversal of the

text: Laschamp event

text: occurring 41,000 years ago during the

text: last glacial period

text: . Geologists observed

text: geomagnetic reversal recorded

text: in volcanic rocks, through

text: magnetostratigraphy correlation

text: (see

text: natural remanent magnetization

text: ) and their signature can be seen as parallel linear magnetic anomaly stripes on the seafloor. These stripes provide quantitative information on

text: seafloor spreading

text: , a part of

text: plate tectonics

text: . They are the basis of

text: magnetostratigraphy

text: , which correlates magnetic reversals with other stratigraphies to construct geologic time scales. In addition, the

text: magnetization in rocks

text: can be used to measure the motion of continents.

text: Many animals use magnetic orientation based on the Earth's magnetic field to find their way home. This is usually used together with other methods, such as a sun compass, as in bird migration and in the case of turtles. This is also commonly used when no other methods are available, as in the case of lobsters, which live underwater, and mole rats, which home through their underground burrows.

text: Many animals use

text: magnetic

text: orientation based on the

text: Earth's magnetic field

text: to find their way home. This is usually used together with other methods, such as a sun compass, as in

text: bird migration

text: and in the case of turtles. This is also commonly used when no other methods are available, as in the case of

text: lobster

text: s, which live underwater, and

text: mole rat

text: s, which home through their underground

text: burrow

text: s.

text: As with most traditional compasses, directional measurements are made in reference to the Earth's magnetic field and will thus run into difficulties if in a region of locally abnormal magnetism.  For example, if the user is near an outcrop that contains magnetite or some other iron-bearing material, compass readings can be affected anywhere from several inches from the outcrop to tens of yards away (depending on the strength of the magnetic field).  Since they are measured only using a rotating level, dip measurements are unaffected by magnetic fields.

text: As with most traditional compasses, directional measurements are made in reference to the

text: Earth's magnetic field

text: and will thus run into difficulties if in a region of locally abnormal

text: magnetism

text: .  For example, if the user is near an outcrop that contains

text: magnetite

text: or some other

text: iron

text: -bearing material, compass readings can be affected anywhere from several inches from the

text: outcrop

text: to tens of yards away (depending on the strength of the magnetic field).  Since they are measured only using a rotating

text: level

text: , dip measurements are unaffected by magnetic fields.

text: Alnico alloys can be magnetised to produce strong magnetic fields, and have a high coercivity (resistance to demagnetization), and thus make strong permanent magnets. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500 gauss (0.15 tesla), or about 3000 times the strength of Earth's magnetic field. Some brands of alnico are isotropic and can be efficiently magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation. Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types. Alnico's remanence (B) may exceed 12,000 G (1.2 T), its coercivity (H) can be up to 1000 oersted (80 kA/m), its energy product ((BH)) can be up to 5.5 MG·Oe (44 T·A/m). This means alnico can produce a strong magnetic flux in closed magnetic circuits, but has relatively small resistance against demagnetization.  The field strength at the poles of any permanent magnet depends very much on the shape and is usually well below the remanence strength of the material.

text: Alnico alloys can be magnetised to produce strong

text: magnetic field

text: s, and have a high coercivity (resistance to demagnetization), and thus make strong permanent magnets. Of the more commonly available magnets, only

text: rare-earth magnet

text: s such as

text: neodymium

text: and

text: samarium-cobalt

text: are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500

text: gauss

text: tesla

text: ), or about 3000 times the strength of Earth's magnetic field. Some brands of alnico are

text: isotropic

text: and can be efficiently magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation. Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types. Alnico's

text: remanence

text: (B) may exceed 12,000 G (1.2 T), its coercivity (H) can be up to 1000 oersted (80 kA/m), its energy product ((BH)) can be up to 5.5 MG·Oe (44 T·A/m). This means alnico can produce a strong magnetic flux in closed magnetic circuits, but has relatively small resistance against demagnetization.  The field strength at the poles of any permanent magnet depends very much on the shape and is usually well below the remanence strength of the material.

text: A magnetic anomaly detector (MAD) is an instrument used to detect minute variations in the Earth's magnetic field. The term refers specifically to magnetometers used by military forces to detect submarines (a mass of ferromagnetic material creates a detectable disturbance in the magnetic field); military MAD equipment is a descendent of geomagnetic survey or aeromagnetic survey instruments used to search for minerals by detecting their disturbance of the normal earth-field.

text: A magnetic anomaly detector (MAD) is an instrument used to detect minute variations in the

text: Earth's magnetic field

text: . The term refers specifically to

text: magnetometer

text: s used by military forces to detect

text: submarine

text: s (a mass of

text: ferromagnetic

text: material creates a detectable disturbance in the

text: magnetic field

text: ); military MAD equipment is a descendent of

text: geomagnetic

text: survey

text: or

text: aeromagnetic survey

text: instruments used to search for

text: mineral

text: s by detecting their disturbance of the normal earth-field.

text: Magnetic fields can play a significant role as a source of orbit perturbation as was seen in the Long Duration Exposure Facility. Like gravity, the magnetic field of the Earth can be expressed through spherical harmonics as shown below:

text: Magnetic fields can play a significant role as a source of orbit perturbation as was seen in the

text: Long Duration Exposure Facility

text: . Like gravity, the magnetic field of the Earth can be expressed through spherical harmonics as shown below:

text: The use of 'West' to mean the 'out' direction (actually 'out' → 'West' → 'sunset' → 'down', i.e. 'out of view') may appear unnecessarily contrived. Previously, as related in the first reference cited above, Faraday had used the more straightforward term "exode" (the doorway where the current exits). His motivation for changing it to something meaning 'the West electrode' (other candidates had been "westode", "occiode" and "dysiode") was to make it immune to a possible later change in the direction convention for current, whose exact nature was not known at the time. The reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant. He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. This made the internal current East to West as previously mentioned, but in the event of a later convention change it would have become West to East, so that the West electrode would not have been the 'way out' any more. Therefore, "exode" would have become inappropriate, whereas "cathode" meaning 'West electrode' would have remained correct with respect to the unchanged direction of the actual phenomenon underlying the current, then unknown but, he thought, unambiguously defined by the magnetic reference. In retrospect the name change was unfortunate, not only because the Greek roots alone do not reveal the cathode's function any more, but more importantly because, as we now know, the Earth's magnetic field direction on which the "cathode" term is based is subject to reversals whereas the current direction convention on which the "exode" term was based has no reason to change in the future.

text: The use of 'West' to mean the 'out' direction (actually 'out' → 'West' → 'sunset' → 'down', i.e. 'out of view') may appear unnecessarily contrived. Previously, as related in the first reference cited above, Faraday had used the more straightforward term "exode" (the doorway where the current exits). His motivation for changing it to something meaning 'the West electrode' (other candidates had been "westode", "occiode" and "dysiode") was to make it immune to a possible later change in the direction convention for

text: current

text: , whose exact nature was not known at the time. The reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant. He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical

text: magnetizing current loop

text: around the local line of latitude which would induce a magnetic

text: dipole

text: field oriented like the Earth's. This made the internal current East to West as previously mentioned, but in the event of a later convention change it would have become West to East, so that the West electrode would not have been the 'way out' any more. Therefore, "exode" would have become inappropriate, whereas "cathode" meaning 'West electrode' would have remained correct with respect to the unchanged direction of the actual phenomenon underlying the current, then unknown but, he thought, unambiguously defined by the magnetic reference. In retrospect the name change was unfortunate, not only because the Greek roots alone do not reveal the cathode's function any more, but more importantly because, as we now know, the Earth's magnetic field direction on which the "cathode" term is based is subject to

text: reversals

text: whereas the

text: current

text: direction convention on which the "exode" term was based has no reason to change in the future.

text: The interaction between the solar wind and the Earth's magnetic field has a number of consequences. In brief, these are the formation of the terrestrial Magnetosphere, the provision of energy and matter to the [magnetosphere], and the powering of large-scale electric currents and the closely related phenomenon of the aurora. Near-Earth space physical processes are of interest for economic reasons and for what we can learn about our environment and the cosmos. These processes are connected along the magnetic field to the Earth's ionosphere, where they lead to the aurora, heating, modification of composition, and large-scale plasma motions. All of these ionospheric processes are interesting in their own right. In addition, there is an increasing understanding of the correspondence between inospheric processes and processes going  on further out in near-Earth space. In this way, observations of the ionospheric processes can be used to in turn remote sense dynamics in near-Earth space.

text: The interaction between the

text: solar wind

text: and the

text: Earth's magnetic field

text: has a number of consequences. In brief, these are the formation of the terrestrial

text: Magnetosphere

text: , the provision of energy and matter to the [magnetosphere], and the powering of large-scale electric currents and the closely related phenomenon of the

text: aurora

text: . Near-Earth

text: space physical

text: processes are of interest for

text: economic reasons

text: and for what we can learn about our environment and the cosmos. These processes are connected along the magnetic field to the Earth's

text: ionosphere

text: , where they lead to the aurora, heating, modification of composition, and large-scale

text: plasma

text: motions. All of these

text: ionospheric

text: processes are interesting in their own right. In addition, there is an increasing understanding of the correspondence between

text: inospheric

text: processes and processes going  on further out in near-Earth space. In this way, observations of the

text: ionospheric

text: processes can be used to in turn remote sense dynamics in near-Earth space.

text: Protons are charged particles and are therefore influenced by magnetic fields. When the energetic protons leave the Sun, they preferentially follow (or are guided by) the Sun's powerful magnetic field. When solar protons enter the Earth's magnetosphere where the magnetic fields are stronger than solar magnetic fields, they are guided by the Earth's magnetic field into the polar regions where the majority of the Earth's magnetic field lines enter and exit.

text: Protons are charged particles and are therefore influenced by magnetic fields. When the energetic protons leave the

text: Sun

text: , they preferentially follow (or are guided by) the Sun's powerful magnetic field. When solar protons enter the

text: Earth's magnetosphere

text: where the magnetic fields are stronger than solar magnetic fields, they are guided by the Earth's magnetic field into the polar regions where the majority of the Earth's magnetic field lines enter and exit.

text: Magnetostratigraphy is also used to determine age. This technique uses the pattern of magnetic polarity zones of CRBG layers by comparison to the magnetic polarity timescale. The samples are analyzed to determine their characteristic remanent magnetization from the Earth's magnetic field at the time a stratum was deposited. This is possible as magnetic minerals precipitate in the melt (crystallize), they orient themselves with Earth's magnetic field.

text: Magnetostratigraphy

text: is also used to determine age. This technique uses the pattern of magnetic polarity zones of CRBG layers by comparison to the magnetic polarity timescale. The samples are analyzed to determine their characteristic remanent magnetization from the Earth's magnetic field at the time a stratum was deposited. This is possible as magnetic minerals precipitate in the melt (crystallize), they orient themselves with Earth's magnetic field.

text: Remote magnetic navigation operates by using two large magnets placed on either side of the patient, and alterations in the magnetic field produced by the magnets deflects the tips of catheters within the patient to the desired direction. The EP operates the catheter placement and direction in a shielded room with screens and a joystick. The catheter itself is advanced by the joystick, instead of the physician's hands. Stereotaxis offers software which enables automated mapping and other advantages through its Navigant suite. Due to the lack of irrigated catheters, completing ablation procedures with magnetic navigation has been difficult, especially in the left atrium. Magnetic irrigated catheters for Stereotaxis's Niobe MNS have been recently approved by the FDA on February 26, 2009, and the catheters have been commercially available in Europe since November, 2008. Dr. Andrea Natale remarked that the new magnetic irrigated catheters are "revolutionary" for the treatment of arrhythmias. It is unclear what kind of procedure Dr. Natale performed and if it was included within the FDA approved procedures.  As of January 2009, 18,000 total clinical cases were performed by magnetic navigation according to Stereotaxis's website, with a complication rate of less than 0.1%, representing a minute fraction of complications occurring with manual and other robotic navigation systems. The Niobe has yet to report an instance of perforation during a procedure. The long-term success, 6 months to 1 year after ablation, and cost effectiveness, has yet to have been approved by multicenter trials; however, single center studies have proven the Niobe superior in both categories when compared to manual techniques.

text: Sharks can detect weak electric fields in their environment using ampullary receptors in to find their prey. A study by Kalmijn et al. 1971 observed this action.  Kalmijn used a type of flatfish, called a plaice as a living source of food along with the electrodes and the whiting pieces. He saw that sharks could detect plaice buried under the sand, and would smoothly change direction to where the plaice lay hidden and attack it. To determine if sharks were using electric fields or smell to detect their prey, he devised an experiment. He used the shark species Scyliorhinus canicula and the ray species Raja clavata. He created an agar chamber, which would hold a plaice (small fish), and an opening tube downstream to separate any smells. The agar chamber would enclose the plaice on all sides. The agar does not allow odors to pass, but it does allow electric field to pass through it. Kalmijn would place the plaice in the agar and bury it underneath the sand to eliminate any visual cues. When sharks were in feeding mode, they would locate the agar with the plaice underneath it and attack it near the head region (where bioelectric fields are thought to originate). If chopped up bits of whiting were put in the agar chamber, the shark would try to locate the prey via smell coming out of the outlet tube. Also, if the plaice was put in an agar chamber and covered with polyethylene film, the sharks could no longer detect the plaice. The polyethylene layer inhibits the bioelectric fields and prevents the shark from using passive electrolocation to hunt its prey. One additional behavior observed in sharks is their orientation to the Earth's magnetic field. The Earth’s magnetic field acts as a uniform field, B. When the shark swim through the Earth's magnetic field with its own velocity v, the shark induces its own electric current. Sharks swimming though the Earth's magnetic field create a voltage gradient that could act as a physical basis for compass orientation.

text: Sharks can detect weak electric fields in their environment using ampullary receptors in to find their prey. A study by Kalmijn et al. 1971 observed this action.  Kalmijn used a type of flatfish, called a

text: plaice

text: The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole. The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is , with global magnetic dipole moment of . The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.

text: The main part of

text: Earth's magnetic field

text: is generated in the core, the site of a

text: dynamo

text: process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a

text: dipole

text: . The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is , with global

text: magnetic dipole moment

text: of . The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes

text: secular variation

text: of the main field and

text: field reversals

text: at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.

text: A reversed field pinch is formed similarly to other toroidal pinch devices, by driving current through the plasma from an associated capacitor bank or other high-current power source. In a tokamak the toroidal field is much stronger than the poloidal field, but in an RFP it's just the opposite. In fact, in an RFP the externally applied toroidal field is switched off shortly after startup. The plasma in an RFP is also much closer to the wall than in a Tokamak. This permits a peculiar arrangement of the magnetic field lines, which will 'relax' into a new state such that the total magnetic energy in the plasma is minimized and the total magnetic helicity is conserved. The relaxed state, called a Taylor state, is marked by a peculiar arrangement of magnetic field lines where the toroidal magnetic field at the edge spontaneously reverses direction.

text: A reversed field pinch is formed similarly to other toroidal pinch devices, by driving current through the plasma from an associated capacitor bank or other high-current power source. In a

text: tokamak

text: the toroidal field is much stronger than the poloidal field, but in an RFP it's just the opposite. In fact, in an RFP the externally applied toroidal field is switched off shortly after startup. The plasma in an RFP is also much closer to the wall than in a Tokamak. This permits a peculiar arrangement of the magnetic field lines, which will 'relax' into a new state such that the total magnetic energy in the plasma is minimized and the total

text: magnetic helicity

text: is conserved. The relaxed state, called a Taylor state, is marked by a peculiar arrangement of magnetic field lines where the toroidal magnetic field at the edge spontaneously reverses direction.

text: Rare-earth magnets are strong permanent magnets made from alloys of rare earth elements (elements in the lanthanide series, plus scandium and yttrium).  Developed in the 1970s and '80s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.  There are two types: neodymium magnets and samarium-cobalt magnets. Magnetostrictive rare-earth magnets such as Terfenol-D also have applications—e.g. in loudspeakers. Rare earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder.

text: Rare-earth magnets are strong

text: permanent magnet

text: s made from

text: alloy

text: s of

text: rare earth element

text: s (elements in the

text: lanthanide

text: series, plus

text: scandium

text: and

text: yttrium

text: ).  Developed in the 1970s and '80s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as

text: ferrite

text: or

text: alnico

text: magnets. The

text: magnetic field

text: typically produced by rare-earth magnets can exceed 1.4

text: teslas

text: , whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.  There are two types:

text: neodymium magnet

text: s and

text: samarium-cobalt magnet

text: s.

text: Magnetostrictive

text: rare-earth magnets such as

text: Terfenol-D

text: also have applications—e.g. in

text: loudspeaker

text: s. Rare earth magnets are extremely

text: brittle

text: and also vulnerable to

text: corrosion

text: , so they are usually

text: plated

text: or

text: coated

text: to protect them from breaking, chipping, or crumbling into powder.

text: In some simulations, this leads to an instability in which the magnetic field spontaneously flips over into the opposite orientation. This scenario is supported by observations of the solar magnetic field, which undergoes spontaneous reversals every 9–12 years. However, with the Sun it is observed that the solar magnetic intensity greatly increases during a reversal, whereas reversals on Earth seem to occur during periods of low field strength.

text: In some simulations, this leads to an instability in which the magnetic field spontaneously flips over into the opposite orientation. This scenario is supported by observations of the

text: solar magnetic field

text: , which undergoes spontaneous

text: reversals

text: every 9–12 years. However, with the Sun it is observed that the solar magnetic intensity greatly increases during a reversal, whereas reversals on Earth seem to occur during periods of low field strength.

text: The central solenoid and toroidal field superconducting magnets designed for the ITER fusion reactor use niobium-tin (NbSn) as a superconductor. The Central Solenoid coil will carry 46 kA and produce a field of 13.5 teslas. The 18 Toroidal Field coils at max field of 11.8 T will store 41 GJ (total?). They have been tested at a record 80 kA. Other lower field ITER magnets (PF and CC) will use niobium-titanium. Most of the ITER magnets will have their field varied many times per hour.

text: The central solenoid and toroidal field superconducting magnets designed for the

text: ITER

text: fusion reactor use

text: niobium-tin

text: (NbSn) as a superconductor. The Central Solenoid coil will carry 46 kA and produce a field of 13.5 teslas. The 18 Toroidal Field coils at max field of 11.8 T will store 41 GJ (total?). They have been tested at a record 80 kA. Other lower field ITER magnets (PF and CC) will use

text: niobium-titanium

text: . Most of the ITER magnets will have their field varied many times per hour.

text: The fundamental basis for induced voltage in a magnetic field comes from Faraday's law describing an induced electromotive force (EMF) as follows:Emf = -N (∆Φb / ∆t)(Nave, C. R. 2011).This implies that as the number of magnetic flux lines increase or decrease there is a subsequent induced voltage of negative or positive polarity.  However the relationship of electric forces and magnetic forces were summed up in Lorentz Force Law as F as follows:F = qE + qv x BHere all three forces were found to be perpendicular to each other (Nave, a, 2011).  Thus Lorentz gave specially oriented direction to each of the forces allowing us to predict the direction of forces within the inductive pump architecture.  Salamey further investigated the relationship of magnetic flux to circumferential area about the magnetic field where most of the magnetic forces were found to create mechanical forces used to direct the motion of the piston.  Salamey further describes in his second patent the incorporation of a magnetic field gap.  The gap is defined as a region of non-magnetic conduction circumferentially located at either end of the piston bore.  The magnetic gap allows for increased propagation of magnetic flux through the magnetic piston body causing an increased force pulling the piston towards the magnetic end-pole (Salamey, 1999).

text: The fundamental basis for induced voltage in a magnetic field comes from

text: Faraday's law

text: describing an induced electromotive force (EMF) as follows:Emf = -N (∆Φb / ∆t)(Nave, C. R. 2011).This implies that as the number of magnetic flux lines increase or decrease there is a subsequent induced voltage of negative or positive polarity.  However the relationship of electric forces and magnetic forces were summed up in

text: Lorentz Force Law

text: as F as follows:F = qE + qv x BHere all three forces were found to be perpendicular to each other (Nave, a, 2011).  Thus Lorentz gave specially oriented direction to each of the forces allowing us to predict the direction of forces within the inductive pump architecture.  Salamey further investigated the relationship of magnetic flux to circumferential area about the magnetic field where most of the magnetic forces were found to create mechanical forces used to direct the motion of the piston.  Salamey further describes in his second patent the incorporation of a magnetic field gap.  The gap is defined as a region of non-magnetic conduction circumferentially located at either end of the piston bore.  The magnetic gap allows for increased propagation of magnetic flux through the magnetic piston body causing an increased force pulling the piston towards the magnetic end-pole (Salamey, 1999).

text: If an inductor is connected across a charged capacitor, current will start to flow through the inductor, building up a magnetic field around it and reducing the voltage on the capacitor. Eventually all the charge on the capacitor will be gone and the voltage across it will reach zero. However, the current will continue, because inductors resist changes in current. The current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. Due to Faraday's law, the EMF which drives the current is caused by a decrease in the magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field. When the magnetic field is completely dissipated the current will stop and the charge will again be stored in the capacitor, with the opposite polarity as before. Then the cycle will begin again, with the current flowing in the opposite direction through the inductor.

text: If an inductor is connected across a charged capacitor, current will start to flow through the inductor, building up a magnetic field around it and reducing the voltage on the capacitor. Eventually all the charge on the capacitor will be gone and the voltage across it will reach zero. However, the current will continue, because inductors resist changes in current. The current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. Due to

text: Faraday's law

text: , the

text: EMF

text: which drives the current is caused by a decrease in the magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field. When the magnetic field is completely dissipated the current will stop and the charge will again be stored in the capacitor, with the opposite polarity as before. Then the cycle will begin again, with the current flowing in the opposite direction through the inductor.

text: The Galileo craft made six close flybys of Ganymede from 1995–2000 (G1, G2, G7, G8, G28 and G29) and discovered that Ganymede has a permanent (intrinsic) magnetic moment independent of the Jovian magnetic field. The value of the moment is about , which is three times larger than the magnetic moment of Mercury. The magnetic dipole is tilted with respect to the rotational axis of Ganymede by 176°, which means that it is directed against the Jovian magnetic moment. Its north pole lies below the orbital plane. The dipole magnetic field created by this permanent moment has a strength of 719 ± 2 nT at Ganymede's equator, which should be compared with the Jovian magnetic field at the distance of Ganymede—about 120 nT. The equatorial field of Ganymede is directed against the Jovian field, meaning reconnection is possible. The intrinsic field strength at the poles is two times that at the equator—1440 nT.The permanent magnetic moment carves a part of space around Ganymede, creating a tiny magnetosphere embedded inside that of Jupiter; it is the only moon in the Solar System known to possess the feature. Its diameter is 4–5 R (R = 2,631.2 km). The Ganymedian magnetosphere has a region of closed field lines located below 30° latitude, where charged particles (electrons and ions) are trapped, creating a kind of radiation belt. The main ion species in the magnetosphere is single ionized oxygen—O—which fits well with Ganymede's tenuous oxygen atmosphere. In the polar cap regions, at latitudes higher than 30°, magnetic field lines are open, connecting Ganymede with Jupiter's ionosphere. In these areas, the energetic (tens and hundreds of kiloelectronvolt) electrons and ions have been detected, which may cause the auroras observed around the Ganymedian poles. In addition, heavy ions continuously precipitate on Ganymede's polar surface, sputtering and darkening the ice.

text: The Galileo craft made six close flybys of Ganymede from 1995–2000 (G1, G2, G7, G8, G28 and G29) and discovered that Ganymede has a permanent (intrinsic)

text: magnetic moment

text: independent of the Jovian magnetic field. The value of the moment is about , which is three times larger than the

text: magnetic moment of Mercury

text: . The magnetic dipole is tilted with respect to the rotational axis of Ganymede by 176°, which means that it is directed against the Jovian magnetic moment. Its north pole lies below the

text: orbital plane

text: . The

text: dipole magnetic field

text: created by this permanent moment has a strength of 719 ± 2

text: nT

text: at Ganymede's equator, which should be compared with the Jovian magnetic field at the distance of Ganymede—about 120 nT. The equatorial field of Ganymede is directed against the Jovian field, meaning

text: reconnection

text: is possible. The intrinsic field strength at the poles is two times that at the equator—1440 nT.The permanent magnetic moment carves a part of space around Ganymede, creating a tiny

text: magnetosphere

text: embedded inside

text: that of Jupiter

text: ; it is the only moon in the Solar System known to possess the feature. Its diameter is 4–5 R (R = 2,631.2 km). The Ganymedian magnetosphere has a region of closed

text: field line

text: s located below 30°

text: latitude

text: , where

text: charged particle

text: s (

text: electron

text: s and

text: ion

text: s) are trapped, creating a kind of

text: radiation belt

text: . The main ion species in the magnetosphere is single ionized

text: oxygen

text: —O—which fits well with Ganymede's tenuous oxygen

text: atmosphere

text: . In the polar cap regions, at latitudes higher than 30°, magnetic field lines are open, connecting Ganymede with Jupiter's

text: ionosphere

text: . In these areas, the energetic (tens and hundreds of

text: kiloelectronvolt

text: ) electrons and ions have been detected, which may cause the

text: aurora

text: s observed around the Ganymedian poles. In addition, heavy ions continuously precipitate on Ganymede's polar surface,

text: sputtering

text: and darkening the ice.

text: The Group’s operations are based on a multi-format, multi-banner, multi-channel approach and a dual retailing/property business model.

text: The leading world chromite ore-producing countries in 2008 were India (almost 4 Mt), Kazakhstan (more than 3 Mt), and South Africa (almost 10 Mt). More than 94% of chromite ore production was smelted in electric-arc furnaces to produce ferrochromium for the metallurgical industry. The leading world ferrochromium-producing countries in 2008 were China (more than 1 Mt), Kazakhstan (more than 1 Mt), and South Africa (more than 3 Mt). India and Russia each produced in excess of 0.5 Mt of ferrochromium. Most of the 7.84 Mt of ferrochromium produced worldwide was consumed in the manufacture of stainless steel which exceeded 26 Mt in 2008.Production for this is very economical.

text: In engineering applications the residual magnetization is often measured using a B-H Analyzer, which measures the response to an AC magnetic field  (as in Fig. 1). This is represented by a flux density B. This value of remanence is one of the most important parameters characterizing permanent magnets; it measures the strongest magnetic field they can produce. Neodymium magnets, for example, have a remanence approximately equal to 1.3 teslas.

text: In engineering applications the residual magnetization is often measured using a

text: B-H Analyzer

text: , which measures the response to an AC magnetic field  (as in Fig. 1). This is represented by a

text: flux density

text: B. This value of remanence is one of the most important parameters characterizing

text: permanent magnet

text: s; it measures the strongest magnetic field they can produce.

text: Neodymium magnets

text: , for example, have a remanence approximately equal to 1.3

text: teslas

text: where n are the stoichiometric coefficients of the reactants in the equilibrium equation, and m are the coefficients of the products. The value of δG for these reactions is a function of the chemical potentials of all the species.

text: where n are the

text: stoichiometric coefficient

text: s of the reactants in the equilibrium equation, and m are the coefficients of the products. The value of δG for these reactions is a function of the chemical potentials of all the species.

text: The Earth’s magnetic field is a potential map cue as the field varies in both strength and direction over the Earth’s surface Manipulations of the ambient magnetic field are rather difficult, although Keeton (1971) and Ioalé (1984) did report that magnets caused disorientation in pigeons when they were released under total overcast.  This first indication for magnetic compass orientation in homing was later supported by other studies, which reversed the field around the head of the pigeon using battery operated coils.  Though the coils had little effect in clear conditions, their effect under overcast conditions was dependent on the direction of the current.  Another observation consistent with the idea of a geomagnetic map is the shift in the initial bearings of pigeons that occurs when the field increases during magnetic storms.  In magnetic anomalies too, pigeons are disoriented, even under sunny conditions.

text: The Earth’s magnetic field is a potential map cue as the field varies in both strength and direction over the Earth’s surface Manipulations of the ambient magnetic field are rather difficult, although

text: Keeton

text: (1971) and Ioalé (1984) did report that magnets caused disorientation in pigeons when they were released under total overcast.  This first indication for magnetic compass orientation in homing was later supported by other studies, which reversed the field around the head of the pigeon using battery operated

text: coils

text: .  Though the coils had little effect in clear conditions, their effect under overcast conditions was dependent on the direction of the current.  Another observation consistent with the idea of a geomagnetic map is the shift in the initial bearings of pigeons that occurs when the field increases during magnetic storms.  In

text: magnetic anomalies

text: too, pigeons are disoriented, even under sunny conditions.

text: Programmes under the EEA and Norway Grants 2009-2014 may run until 2017. More than 80 programmes are implemented in cooperation with public entities from the Donor states. More than 20% of the projects have partners from either Norway, Iceland or Liechtenstein. A full overview of projects are available on the EEA and Norway Grants project portal.

text: Deira Island is a group of artificial islands in Dubai, United Arab Emirates. The project was initially planned to be  part of the Palm Islands and was called 'Palm Deira'.

text: Deira Island is a group of

text: artificial island

text: s in

text: Dubai

text: United Arab Emirates

text: . The project was initially planned to be  part of the

text: Palm Islands

text: and was called 'Palm Deira'.

text: Viborg Power Station () is a natural gas-fired power station operated by Energi Viborg in Viborg, Denmark.

text: Viborg Power Station () is a

text: natural gas

text: -fired power station operated by

text: Energi Viborg

text: in

text: Viborg

text: Denmark

text: An Byeong-hun, Matteo Manassero

text: An Byeong-hun

text: Matteo Manassero

text: The Basimba people have a Chishimba stone and this stone represents the Chishimba spirit which came from Buluba and is related to the institution of kingship. Its absence constitutes the absence of power. According to Traditional African religions and Veneration of the dead ,the Basimba people practice both Totem and Animal worship, dedicated to the Chishimba spirit which is synonymous to kingship. Its importance in the institution of kingship is similar to that attached to Shila tradition. The Chishimba stone is kept in a specially prepared basket called Embuga. It is wrapped with bark cloth and kept in a specifically prepared shrine (Esabbo lye jembe lye Chishimba) dedicated to the spirit.

text: The Basimba people have a Chishimba stone and this stone represents the Chishimba spirit which came from Buluba and is related to the institution of kingship. Its absence constitutes the absence of power. According to

text: Traditional African religions

text: and

text: Veneration of the dead

text: ,the Basimba people practice both

text: Totem

text: and

text: Animal worship

text: , dedicated to the Chishimba spirit which is synonymous to kingship. Its importance in the institution of kingship is similar to that attached to Shila tradition. The Chishimba stone is kept in a specially prepared basket called Embuga. It is wrapped with bark cloth and kept in a specifically prepared shrine (Esabbo lye jembe lye Chishimba) dedicated to the spirit.

text: There have also been two traveling exhibitions, in 2000 and 2003, enabling up to 50 selected works to be shown in regional galleries around Australia, promoting the richness of Aboriginal and Torres Strait Islander art to a wide audience across the country.

text: Besides translation from Homer (Iliad, books i, ii, etc.) and Aeschylus (Agamemnon the King), and works in the Book of Common Prayer, including a paraphrase on a translation of the same in Latin, he edited the Breviarium Aberdonense 1854; and published a pamphlet on Hymns and Hymn Books, 1858; and (with Dr. H.J. Gauntlett) the Church Hymn and Tune Book, 1852, 2nd. ed. 1855. The hymns in the last work are chiefly translations by Blew of Latin hymns. They were written from 1845 to 1852, and printed on fly-sheets for the use of his congregation. Many of these translations have come into common use.

text: Besides translation from

text: Homer

text: (Iliad, books i, ii, etc.) and

text: Aeschylus

text: Agamemnon the King

text: ), and works in the

text: Book of Common Prayer

text: , including a paraphrase on a translation of the same in Latin, he edited the Breviarium Aberdonense 1854; and published a pamphlet on Hymns and Hymn Books, 1858; and (with Dr.

text: H.J. Gauntlett

text: ) the Church Hymn and Tune Book, 1852, 2nd. ed. 1855. The hymns in the last work are chiefly translations by Blew of Latin hymns. They were written from 1845 to 1852, and printed on fly-sheets for the use of his congregation. Many of these translations have come into common use.

text: Established in 1991, Roberson Wine specialises in wines from France and California, selling online to private individuals and wholesale to restaurants and off-trade businesses. It holds regular tastings of fine wine in its Earls Court premises. Roberson Wine closed its Kensington Store at the end of August 2015 and now operates entirely out of its offices in Earls Court. It is situated above central London's only working winery, London Cru, also founded by Cliff Roberson, owner of Roberson Wine.

text: Established in 1991, Roberson Wine specialises in wines from France and California, selling online to private individuals and wholesale to restaurants and off-trade businesses. It holds regular tastings of fine wine in its

text: Earls Court

text: premises. Roberson Wine closed its Kensington Store at the end of August 2015 and now operates entirely out of its offices in Earls Court. It is situated above central London's only working winery, London Cru, also founded by Cliff Roberson, owner of Roberson Wine.

text: With these considerations, the differential equation governing the behavior of a magnetic moment in the presence of an applied magnetic field with damping can be written in the most familiar form of the Landau-Lifshitz-Gilbert equation,

text: With these considerations, the differential equation governing the behavior of a magnetic moment in the presence of an applied magnetic field with damping can be written in the most familiar form of the

text: Landau-Lifshitz-Gilbert equation

text: From Faraday's law, this assumption implies the absence or near-absence of time-varying magnetic fields:

text: From

text: Faraday's law

text: , this assumption implies the absence or near-absence of time-varying magnetic fields: