An Etymological Dictionary of Astronomy and Astrophysics

Half of the vertex angle of the → Mach cone
generated by a body in → supersonic flight.
It is given by sin μ = (a/v), where a is the speed of the sound waves and v the velocity of the object. In terms of Mach number: μ = asin (1/M). The Mach angle diminishes with the object velocity. For M = 1 it is 90°, for M = 2, it is 30°, and for M = 5, its is 11.5°.

See also: → Mach number; → angle.

Half of the vertex angle of the → Mach cone
generated by a body in → supersonic flight.
It is given by sin μ = (a/v), where a is the speed of the sound waves and v the velocity of the object. In terms of Mach number: μ = asin (1/M). The Mach angle diminishes with the object velocity. For M = 1 it is 90°, for M = 2, it is 30°, and for M = 5, its is 11.5°.

See also: → Mach number; → angle.

The cone that confines the pressure disturbance created by a
→ supersonic object moving in a → compressible medium.

See also: → Mach number; → cone.

The cone that confines the pressure disturbance created by a
→ supersonic object moving in a → compressible medium.

See also: → Mach number; → cone.

Same as → shock diamond.

See also: So named because Ernst Mach (1838-1916) was the first to record its existence.

Same as → shock diamond.

See also: So named because Ernst Mach (1838-1916) was the first to record its existence.

The ratio of the speed of a moving object to the → sound speed in the medium through which the object is traveling.

See also: Named after the Austrian physicist Ernst Mach (1838-1916); → number.

The ratio of the speed of a moving object to the → sound speed in the medium through which the object is traveling.

See also: Named after the Austrian physicist Ernst Mach (1838-1916); → number.

The envelope of wave fronts created by a → supersonic source.

See also: → Mach number; → wave.

The envelope of wave fronts created by a → supersonic source.

See also: → Mach number; → wave.

The local → inertial frame and the → inertia of any body results from the distribution of all matter in the Universe. This principle has been neither confirmed nor refuted.

See also: → Mach number; → number.

The local → inertial frame and the → inertia of any body results from the distribution of all matter in the Universe. This principle has been neither confirmed nor refuted.

See also: → Mach number; → number.

1. An apparatus consisting of interrelated parts with separate functions, used in the performance of some kind of work.
   

2. A device that transmits or modifies force or motion.

Etymology (EN): From M.Fr. machine “device, contrivance,” from L. machina “machine, fabric, device, trick,” from Doric Gk. makhana, Attic Gk. mekhane “device, means,” related to mekhos “means, expedient,” from PIE *maghana- “that which enables,” from base *magh- “to be able, have power” (cf. O.C.S. mogo “be able,” O.E. mæg “I can”).

Etymology (PE): Mâšin, loanword from Fr.

1. An apparatus consisting of interrelated parts with separate functions, used in the performance of some kind of work.
   

2. A device that transmits or modifies force or motion.

Etymology (EN): From M.Fr. machine “device, contrivance,” from L. machina “machine, fabric, device, trick,” from Doric Gk. makhana, Attic Gk. mekhane “device, means,” related to mekhos “means, expedient,” from PIE *maghana- “that which enables,” from base *magh- “to be able, have power” (cf. O.C.S. mogo “be able,” O.E. mæg “I can”).

Etymology (PE): Mâšin, loanword from Fr.

A collective term for objects that reside in the → halo of a galaxy (in particular → brown dwarfs) and which do not emit enough radiation to be detected from Earth. MACHOs can be spotted using the technique of → microlensing.

See also: Acronym from Massive Astrophysical Compact Halo Objects.

A collective term for objects that reside in the → halo of a galaxy (in particular → brown dwarfs) and which do not emit enough radiation to be detected from Earth. MACHOs can be spotted using the technique of → microlensing.

See also: Acronym from Massive Astrophysical Compact Halo Objects.

A → Taylor series that is expanded about the reference point zero.

See also: Named after Colin Maclaurin (1698-1746), a Scottish mathematician.

A → Taylor series that is expanded about the reference point zero.

See also: Named after Colin Maclaurin (1698-1746), a Scottish mathematician.

A combining form meaning “large, long, great, excessive,” used in the formation of compound words; opposite of → micro-.

Etymology (EN): From Gk. makros “long, large,” from PIE base *mak-/*mek- “long, thin” (cf. L. macer “lean, thin;” O.N. magr, O.E. mæger “lean, thin”).

Etymology (PE): Dorošt “large; rough, fierce,” from Mid.Pers. društ “harsh, coarse;” O.Pers. darš- “to dare,” daršam (adv.) “mightily;” Av. darš- “to dare,” darši-, daršita- “bold, strong;” cf. Skt. dhars- “to be bold, courageous, to attack,” dhrsita- “bold, daring;” Gk. thrasys “bold;” O.E. durran; E. dare.

A combining form meaning “large, long, great, excessive,” used in the formation of compound words; opposite of → micro-.

Etymology (EN): From Gk. makros “long, large,” from PIE base *mak-/*mek- “long, thin” (cf. L. macer “lean, thin;” O.N. magr, O.E. mæger “lean, thin”).

Etymology (PE): Dorošt “large; rough, fierce,” from Mid.Pers. društ “harsh, coarse;” O.Pers. darš- “to dare,” daršam (adv.) “mightily;” Av. darš- “to dare,” darši-, daršita- “bold, strong;” cf. Skt. dhars- “to be bold, courageous, to attack,” dhrsita- “bold, daring;” Gk. thrasys “bold;” O.E. durran; E. dare.

The great world or Universe; the Universe considered as a whole (opposed to → microcosm).
A representation of a smaller unit or entity by a larger one, presumably of a similar structure.

See also: → macro-; → cosmos.

The great world or Universe; the Universe considered as a whole (opposed to → microcosm).
A representation of a smaller unit or entity by a larger one, presumably of a similar structure.

See also: → macro-; → cosmos.

A stellar → explosion with energies between those of a → nova and a → supernova and observationally distinguished by being brighter than a typical nova (M_V ~ -8 mag) but fainter than a typical supernova (M_V ~ -19 mag) (Kulkarni 2005; arXiv:astro-ph/0510256).

See also: → macro-; → nova.

A stellar → explosion with energies between those of a → nova and a → supernova and observationally distinguished by being brighter than a typical nova (M_V ~ -8 mag) but fainter than a typical supernova (M_V ~ -19 mag) (Kulkarni 2005; arXiv:astro-ph/0510256).

See also: → macro-; → nova.

Of or relating to scales large enough to be visible to the naked eye or under low order of magnification. Compare → microscopic. → microscopic state.

See also: → macro-; → -scope + → -ic.

Of or relating to scales large enough to be visible to the naked eye or under low order of magnification. Compare → microscopic. → microscopic state.

See also: → macro-; → -scope + → -ic.

Same as → macrostate.

See also: → macroscopic; → state.

Same as → macrostate.

See also: → macroscopic; → state.

Statistical physics: A state of a physical system that is described in terms of the system’s overall or average properties at a macroscopic level (→ temperature, → pressure, → density, → internal energy, etc.). A macrostate will generally consist of many different → microstates. In defining a macrostate we ignore what is going on at the microscopic (atomic/molecular) level. The → probability of a certain macrostate is determined by how many microstates correspond to this macrostate. Therefore, the greater the number of microstates which lead to a particular macrostate, the greater the probability of observing that macrostate. Same as → macroscopic state. See also → entropy, → Boltzmann’s entropy formula, → multiplicity.

See also: → macro-; → state.

Statistical physics: A state of a physical system that is described in terms of the system’s overall or average properties at a macroscopic level (→ temperature, → pressure, → density, → internal energy, etc.). A macrostate will generally consist of many different → microstates. In defining a macrostate we ignore what is going on at the microscopic (atomic/molecular) level. The → probability of a certain macrostate is determined by how many microstates correspond to this macrostate. Therefore, the greater the number of microstates which lead to a particular macrostate, the greater the probability of observing that macrostate. Same as → macroscopic state. See also → entropy, → Boltzmann’s entropy formula, → multiplicity.

See also: → macro-; → state.

The broadening of a star’s → spectral lines due to → Doppler shifts from motions of different parts of the star’s atmosphere.

See also: → macro; → turbulence.

The broadening of a star’s → spectral lines due to → Doppler shifts from motions of different parts of the star’s atmosphere.

See also: → macro; → turbulence.

1. Of, relating to, or named from, Ferdinand Magellan (see below).
   

   2. Of or pertaining to characteristic of the → Magellanic Clouds.

See also: Named in honor of Ferdinand Magellan (c. 1480-1521), the Portuguese navigator, who undertook the first voyage around the world. The two Clouds were first described by Magellan’s chronicler Pigafetta, after leaving the Strait of Magellan in 1520; → -ic.

1. Of, relating to, or named from, Ferdinand Magellan (see below).
   

   2. Of or pertaining to characteristic of the → Magellanic Clouds.

See also: Named in honor of Ferdinand Magellan (c. 1480-1521), the Portuguese navigator, who undertook the first voyage around the world. The two Clouds were first described by Magellan’s chronicler Pigafetta, after leaving the Strait of Magellan in 1520; → -ic.

A filament of → neutral hydrogen which connects the → Small Magellanic Cloud and → Large Magellanic Cloud. The Magellanic Bridge appears to result from a → close encounter between these two galaxies some 200 million years ago.

See also: → Magellanic; → bridge.

A filament of → neutral hydrogen which connects the → Small Magellanic Cloud and → Large Magellanic Cloud. The Magellanic Bridge appears to result from a → close encounter between these two galaxies some 200 million years ago.

See also: → Magellanic; → bridge.

Two irregular satellite galaxies of our own Galaxy which are visible from the Southern Hemisphere as misty patches in the night sky. → Large Magellanic Cloud; → Small Magellanic Cloud.

See also: → Magellanic; → cloud.

Two irregular satellite galaxies of our own Galaxy which are visible from the Southern Hemisphere as misty patches in the night sky. → Large Magellanic Cloud; → Small Magellanic Cloud.

See also: → Magellanic; → cloud.

A class of low-mass galaxies with relatively rare features. In particular, these galaxies are characterized by a → stellar bar whose center is displaced from that of the disk and a one-armed spiral. The → Large Magellanic Cloud (LMC) is considered the prototype of this class of objects. However, despite a wealth of data, there is still a good deal of uncertainty concerning the nature of the LMC’s bar.

The majority of the observed Magellanic spirals in the nearby Universe share the LMC’s structure, in particular the evidence of an offset bar and a one-armed spiral structure. A good example of these systems is NGC 3906, which shows evidence of the bar offset from the photometric center of the galaxy by 1.2 kpc (Pardy et al., 2016, ApJ 827, 149).

See also: → Magellanic; → spiral; → galaxy.

A class of low-mass galaxies with relatively rare features. In particular, these galaxies are characterized by a → stellar bar whose center is displaced from that of the disk and a one-armed spiral. The → Large Magellanic Cloud (LMC) is considered the prototype of this class of objects. However, despite a wealth of data, there is still a good deal of uncertainty concerning the nature of the LMC’s bar.

The majority of the observed Magellanic spirals in the nearby Universe share the LMC’s structure, in particular the evidence of an offset bar and a one-armed spiral structure. A good example of these systems is NGC 3906, which shows evidence of the bar offset from the photometric center of the galaxy by 1.2 kpc (Pardy et al., 2016, ApJ 827, 149).

See also: → Magellanic; → spiral; → galaxy.

A thin trail of gas stretching from the → Magellanic System toward our own Galaxy over about 150° on the sky, corresponding to hundreds of thousands of light-years. This gas consists primarily of → neutral hydrogen and is thought to have originated from the Large and Small Magellanic Clouds as a result of tidal interactions with the Milky Way. See, e.g., Fox et al. 2013, arxiv/1304.4240, and references therein.

See also: → Magellanic; → stream.

A thin trail of gas stretching from the → Magellanic System toward our own Galaxy over about 150° on the sky, corresponding to hundreds of thousands of light-years. This gas consists primarily of → neutral hydrogen and is thought to have originated from the Large and Small Magellanic Clouds as a result of tidal interactions with the Milky Way. See, e.g., Fox et al. 2013, arxiv/1304.4240, and references therein.

See also: → Magellanic; → stream.

A system consisting of the → Magellanic Clouds, the → Magellanic Bridge, and the → Magellanic stream.

See also: → Magellanic Clouds; → system.

A system consisting of the → Magellanic Clouds, the → Magellanic Bridge, and the → Magellanic stream.

See also: → Magellanic Clouds; → system.

A → metal-poor, → irregular galaxy like the → Large Magellanic Cloud or the → Small Magellanic Cloud. Other examples are: NGC 4449, NGC 4214, and NGC 3109.

See also: → Magellanic; → type; → galaxy.

A → metal-poor, → irregular galaxy like the → Large Magellanic Cloud or the → Small Magellanic Cloud. Other examples are: NGC 4449, NGC 4214, and NGC 3109.

See also: → Magellanic; → type; → galaxy.

1a) The power of apparently influencing events by using mysterious or supernatural forces.

1b) Mysterious tricks, such as making things disappear and reappear, performed as entertainment.

2. Having or apparently having supernatural powers (OxfordDictionaries.com)

Etymology (EN): M.E. magik(e) “witchcraft,” from O.Fr. magique “magic, magical,” from L.L. magice “sorcery, magic,” from Gk. magike (tekhne “art”), from magos “one of the members of the learned and priestly class,” from O.Pers. magu-, possibly from PIE root *magh- “to be able, have power.”

Etymology (PE): Mid.Pers. yâtûk “wizard, sorcerer;” Av. yātu-

1a) The power of apparently influencing events by using mysterious or supernatural forces.

1b) Mysterious tricks, such as making things disappear and reappear, performed as entertainment.

2. Having or apparently having supernatural powers (OxfordDictionaries.com)

Etymology (EN): M.E. magik(e) “witchcraft,” from O.Fr. magique “magic, magical,” from L.L. magice “sorcery, magic,” from Gk. magike (tekhne “art”), from magos “one of the members of the learned and priestly class,” from O.Pers. magu-, possibly from PIE root *magh- “to be able, have power.”

Etymology (PE): Mid.Pers. yâtûk “wizard, sorcerer;” Av. yātu-

An n × n matrix in which every row, column, and diagonal add up to the same number.

See also: → magic; → square.

An n × n matrix in which every row, column, and diagonal add up to the same number.

See also: → magic; → square.

1. A civil officer charged with the administration of the law.
   

2. A minor judicial officer, as a justice of the peace or the judge of a police court, having jurisdiction to try minor criminal cases and to conduct preliminary examinations of persons charged with serious crimes (Dictionary.com).

Etymology (EN): M.E., from O.Fr. magistrat, from L. magistratus “a magistrate, public functionary,” from magistrare “to serve as a magistrate,” from magister, “chief, director,” → master.

Etymology (PE): Dâdyâr, from dâd, → justice,

• yâr, “assistant, helper,” → gravity assist.

1. A civil officer charged with the administration of the law.
   

2. A minor judicial officer, as a justice of the peace or the judge of a police court, having jurisdiction to try minor criminal cases and to conduct preliminary examinations of persons charged with serious crimes (Dictionary.com).

Etymology (EN): M.E., from O.Fr. magistrat, from L. magistratus “a magistrate, public functionary,” from magistrare “to serve as a magistrate,” from magister, “chief, director,” → master.

Etymology (PE): Dâdyâr, from dâd, → justice,

• yâr, “assistant, helper,” → gravity assist.

1. Molten → rock material that occurs below Earth’s surface.
   

2. Molten material both below and on top of the surface of a → planet.

Etymology (EN): From L. magma “dregs of an ointment,” from Gk. magma “an ointment,” from root of massein “to knead, mold.”

Etymology (PE): Mâgma, loanword from Fr.

1. Molten → rock material that occurs below Earth’s surface.
   

2. Molten material both below and on top of the surface of a → planet.

Etymology (EN): From L. magma “dregs of an ointment,” from Gk. magma “an ointment,” from root of massein “to knead, mold.”

Etymology (PE): Mâgma, loanword from Fr.

A large cavity within the Earth’s → crust containing → magma. When a → vent is opened to the surface, magma is extruded onto the surface as → lava.

See also: → magma; → chamber.

A large cavity within the Earth’s → crust containing → magma. When a → vent is opened to the surface, magma is extruded onto the surface as → lava.

See also: → magma; → chamber.

A metallic chemical element; symbol Mg. Atomic number 12; atomic weight 24.305; melting point about 648.8°C; boiling point about 1,090°C. The Scottish chemist Joseph Black recognized it as a separate element in 1755. In 1808, the English chemist Humphrey Davy obtained the impure metal and in 1831 the French pharmacist and chemist Antoine-Alexandre Brutus Bussy isolated the metal in the pure state.

Etymology (EN): The name originally used was magnium and was later changed to magnesium, which is derived from Magnesia, a district in the northeastern region of Greece called Thessalia.

A metallic chemical element; symbol Mg. Atomic number 12; atomic weight 24.305; melting point about 648.8°C; boiling point about 1,090°C. The Scottish chemist Joseph Black recognized it as a separate element in 1755. In 1808, the English chemist Humphrey Davy obtained the impure metal and in 1831 the French pharmacist and chemist Antoine-Alexandre Brutus Bussy isolated the metal in the pure state.

Etymology (EN): The name originally used was magnium and was later changed to magnesium, which is derived from Magnesia, a district in the northeastern region of Greece called Thessalia.

An object that produces a magnetic field around itself.

Etymology (EN): From L. magnetum (nom. magnes) “lodestone,” from Gk. ho Magnes lithos “the Magnesian stone,” from Magnesia region in Thessaly where magnetized ore was obtained.

Etymology (PE): Âhanrobâ, literally “iron attracting, iron robbing,” from âhan→ iron + robâ agent noun of robudan, robâyidan “to attract, to grab, rob;” Av. urūpaiieinti “to cause racking pain(?);” cf. Skt. rop- “to suffer from abdominal pain,” rurupas “to cause violent pain,” ropaná- “causing racking pain,” rópi- “racking pain;” L. rumpere “to break;” O.E. reofan “to break, tear.”
Meqnâtis, from Ar., from Gk., as above.

An object that produces a magnetic field around itself.

Etymology (EN): From L. magnetum (nom. magnes) “lodestone,” from Gk. ho Magnes lithos “the Magnesian stone,” from Magnesia region in Thessaly where magnetized ore was obtained.

Etymology (PE): Âhanrobâ, literally “iron attracting, iron robbing,” from âhan→ iron + robâ agent noun of robudan, robâyidan “to attract, to grab, rob;” Av. urūpaiieinti “to cause racking pain(?);” cf. Skt. rop- “to suffer from abdominal pain,” rurupas “to cause violent pain,” ropaná- “causing racking pain,” rópi- “racking pain;” L. rumpere “to break;” O.E. reofan “to break, tear.”
Meqnâtis, from Ar., from Gk., as above.

A highly magnetized → neutron star with fields a thousand times stronger than those of → radio pulsars. There are two sub-classes of magnetars, → anomalous X-Ray pulsar (AXP)s and → soft gamma repeater (SGR)s, that were thought for many years to be separate and unrelated objects. In fact
SGRs and AXPs are both neutron stars possessing → magnetic fields of unprecedented strength of 10¹⁴ - 10¹⁶ G, and that show both steady X-ray pulsations as well as soft gamma-ray bursts. Their inferred steady X-ray luminosities are about one hundred times higher than their → spin-down
luminosities, requiring a source of power well beyond the magnetic dipole spin-down that powers → rotation-powered pulsar (RPP)s. New high-energy components discovered in the spectra of a number of AXPs and SGRs require non-thermal particle acceleration and look very similar to high-energy spectral components of young rotation-powered pulsars (A. K. Harding, 2013, Front. Phys. 8, 679).

See also: From magnet, contraction of → magnetic + -(s)tar, from → star.

A highly magnetized → neutron star with fields a thousand times stronger than those of → radio pulsars. There are two sub-classes of magnetars, → anomalous X-Ray pulsar (AXP)s and → soft gamma repeater (SGR)s, that were thought for many years to be separate and unrelated objects. In fact
SGRs and AXPs are both neutron stars possessing → magnetic fields of unprecedented strength of 10¹⁴ - 10¹⁶ G, and that show both steady X-ray pulsations as well as soft gamma-ray bursts. Their inferred steady X-ray luminosities are about one hundred times higher than their → spin-down
luminosities, requiring a source of power well beyond the magnetic dipole spin-down that powers → rotation-powered pulsar (RPP)s. New high-energy components discovered in the spectra of a number of AXPs and SGRs require non-thermal particle acceleration and look very similar to high-energy spectral components of young rotation-powered pulsars (A. K. Harding, 2013, Front. Phys. 8, 679).

See also: From magnet, contraction of → magnetic + -(s)tar, from → star.

Of or pertaining to a magnet or magnetism.

Etymology (EN): From → magnet + → -ic.

Etymology (PE): Meqnâtisi, meqnâti, from meqnâtis, → magnet; âhanrobâyik, from âhanrobâ, → magnet, + → -ik, → -ic.

Of or pertaining to a magnet or magnetism.

Etymology (EN): From → magnet + → -ic.

Etymology (PE): Meqnâtisi, meqnâti, from meqnâtis, → magnet; âhanrobâyik, from âhanrobâ, → magnet, + → -ik, → -ic.

The transport of the magnetic field by a fluid. It is given by the term ∇ x (v x B) in the → induction equation.

See also: → magnetic; → advection.

The transport of the magnetic field by a fluid. It is given by the term ∇ x (v x B) in the → induction equation.

See also: → magnetic; → advection.

The imaginary straight line joining the two → poles of a → magnet.

See also: → magnetic; → meridian.

The imaginary straight line joining the two → poles of a → magnet.

See also: → magnetic; → meridian.

Any configuration of → magnetic fields used in the containment of a → plasma during controlled → thermonuclear reaction experiments.

See also: → magnetic; → bottle.

Any configuration of → magnetic fields used in the containment of a → plasma during controlled → thermonuclear reaction experiments.

See also: → magnetic; → bottle.

The process whereby a star which loses mass slows down under the action of its → magnetic field. The stellar material follows the → magnetic field lines extending well beyond the stellar surface. The material gain → angular momentum and the underlying object is slowed down. Magnetic braking is an efficient mechanism for removing angular momentum from the the rotating object. See also → disk locking.

See also: → magnetic; → braking.

The process whereby a star which loses mass slows down under the action of its → magnetic field. The stellar material follows the → magnetic field lines extending well beyond the stellar surface. The material gain → angular momentum and the underlying object is slowed down. Magnetic braking is an efficient mechanism for removing angular momentum from the the rotating object. See also → disk locking.

See also: → magnetic; → braking.

The failure of numerical star formation calculations to produce rotationally supported → Keplerian disks because of the → magnetic braking effect, when → magnetic fields of strengths comparable to those observed in → molecular clouds are accounted for.

The formation and early evolution of disks is a long-standing fundamental problem in → star formation models. Early work in the field had concentrated on the simpler problem of disk formation from the → collapse of a rotating dense core in the absence of a magnetic field. However, dense star-forming cores are observed to be significantly magnetized. There is increasing theoretical evidence that disk formation is greatly modified, perhaps even suppressed, by a dynamically important magnetic field.

This has been found in analytic studies, axisymmetric numerical models and in 3D calculations using → ideal magnetohydrodynamics. By contrast, recent observations suggest the presence of massive, 50-100 AU disks and evidence for associated → outflows in the earliest (→ class 0) stages of star formation around both low and high mass stars.

Two primary solutions have been proposed: → turbulence and → non-ideal magnetohydrodynamics.

Calculations of the collapse of a massive 100 Msun core have shown that 100 AU scale disk formation in the presence of strong magnetic fields was indeed possible, with some argument over whether this is caused by turbulent reconnection or another mechanism. Studies, using simulations of collapsing 5 Msun cores, have found that turbulence diffuses the strong magnetic field out of the inner regions of the core, and that the non-zero → angular momentum of the turbulence causes a misalignment between the rotation axis and the magnetic field. Both of these effects reduce the magnetic braking, and allow a massive disk to form (Wurster et al. 2016, arxiv/1512.01597 and references therein).

See also: → magnetic; → braking; → catastrophe.

The failure of numerical star formation calculations to produce rotationally supported → Keplerian disks because of the → magnetic braking effect, when → magnetic fields of strengths comparable to those observed in → molecular clouds are accounted for.

The formation and early evolution of disks is a long-standing fundamental problem in → star formation models. Early work in the field had concentrated on the simpler problem of disk formation from the → collapse of a rotating dense core in the absence of a magnetic field. However, dense star-forming cores are observed to be significantly magnetized. There is increasing theoretical evidence that disk formation is greatly modified, perhaps even suppressed, by a dynamically important magnetic field.

This has been found in analytic studies, axisymmetric numerical models and in 3D calculations using → ideal magnetohydrodynamics. By contrast, recent observations suggest the presence of massive, 50-100 AU disks and evidence for associated → outflows in the earliest (→ class 0) stages of star formation around both low and high mass stars.

Two primary solutions have been proposed: → turbulence and → non-ideal magnetohydrodynamics.

Calculations of the collapse of a massive 100 Msun core have shown that 100 AU scale disk formation in the presence of strong magnetic fields was indeed possible, with some argument over whether this is caused by turbulent reconnection or another mechanism. Studies, using simulations of collapsing 5 Msun cores, have found that turbulence diffuses the strong magnetic field out of the inner regions of the core, and that the non-zero → angular momentum of the turbulence causes a misalignment between the rotation axis and the magnetic field. Both of these effects reduce the magnetic braking, and allow a massive disk to form (Wurster et al. 2016, arxiv/1512.01597 and references therein).

See also: → magnetic; → braking; → catastrophe.

Same as → synchrotron radiation.

See also: → magnetic; → bremsstrahlung.

Same as → synchrotron radiation.

See also: → magnetic; → bremsstrahlung.

The phenomenon whereby the presence of a → magnetic field can make a portion of → compressible fluid less dense than its surroundings, so that it floats upward under the influence of gravity. This magnetic buoyancy is thought, in fact, to be the mechanism by which magnetic flux tubes rise through the Sun’s → convection zone and break at the surface in the form of → sunspots. The Sun’s rotation would have a major effect on the rate at which these magnetic flux tubes rise.
The rotation substantially lengthen the time taken for the flux tubes to reach the surface (D. J. Acheson, 1979, Nature 277, 41).

See also: → magnetic; → buoyancy.

The phenomenon whereby the presence of a → magnetic field can make a portion of → compressible fluid less dense than its surroundings, so that it floats upward under the influence of gravity. This magnetic buoyancy is thought, in fact, to be the mechanism by which magnetic flux tubes rise through the Sun’s → convection zone and break at the surface in the form of → sunspots. The Sun’s rotation would have a major effect on the rate at which these magnetic flux tubes rise.
The rotation substantially lengthen the time taken for the flux tubes to reach the surface (D. J. Acheson, 1979, Nature 277, 41).

See also: → magnetic; → buoyancy.

A cataclysmic binary in which the white dwarf primary has a strong magnetic field that radically affects the accretion flow in the system. → polar

See also: → magnetic; → cataclysmic;
→ binary.

A cataclysmic binary in which the white dwarf primary has a strong magnetic field that radically affects the accretion flow in the system. → polar

See also: → magnetic; → cataclysmic;
→ binary.

A transient ejection in the → solar wind having an enhanced field, a large and smooth change in field direction, and a low → proton temperature compared to the ambient proton temperature (L. F. Burlaga, 1995, Interplanetary Magnetohydrodynamics, Oxford Univ. Press, 89-114).

See also: → magnetic; → cloud.

A transient ejection in the → solar wind having an enhanced field, a large and smooth change in field direction, and a low → proton temperature compared to the ambient proton temperature (L. F. Burlaga, 1995, Interplanetary Magnetohydrodynamics, Oxford Univ. Press, 89-114).

See also: → magnetic; → cloud.

→ compass.

See also: → magnetic; → compass.

→ compass.

See also: → magnetic; → compass.

Of magnetic field lines, the condition for them to be connected or the process whereby they become connected or connective.

See also: → magnetic;→ connectivity.

Of magnetic field lines, the condition for them to be connected or the process whereby they become connected or connective.

See also: → magnetic;→ connectivity.

A physical constant relating mechanical and electromagnetic units of measurement. It has the value of 4π × 10^-7 henry per meter. Also called the permeability of free space, or → absolute permeability.

See also: → magnetic; → constant.

A physical constant relating mechanical and electromagnetic units of measurement. It has the value of 4π × 10^-7 henry per meter. Also called the permeability of free space, or → absolute permeability.

See also: → magnetic; → constant.

Thermal → convection modified by the presence of magnetic fields.

See also: → magnetic; → convection.

Thermal → convection modified by the presence of magnetic fields.

See also: → magnetic; → convection.

In terrestrial magnetism, the difference between → true north (the axis around which the earth rotates) and magnetic north (the direction the needle of a compass will point,→ magnetic pole).

See also: → magnetic; → declination.

In terrestrial magnetism, the difference between → true north (the axis around which the earth rotates) and magnetic north (the direction the needle of a compass will point,→ magnetic pole).

See also: → magnetic; → declination.

The process whereby the magnetic field tends to diffuse across the plasma and to smooth out any local inhomogeneities under the influence of a finite resistance in the plasma. For a stationary plasma the → induction equation becomes a pure → diffusion equation:

∂B/∂t = D_m∇²B, where

D_m = (μ₀σ₀)^-1 is the → magnetic diffusivity.

See also: → magnetic; → diffusion.

The process whereby the magnetic field tends to diffuse across the plasma and to smooth out any local inhomogeneities under the influence of a finite resistance in the plasma. For a stationary plasma the → induction equation becomes a pure → diffusion equation:

∂B/∂t = D_m∇²B, where

D_m = (μ₀σ₀)^-1 is the → magnetic diffusivity.

See also: → magnetic; → diffusion.

The → diffusion coefficient for a magnetic field. It is expressed as: η = 1/(μ₀σ), where μ₀ is the
→ magnetic permeability and σ the
→ conductivity.

See also: → magnetic; → diffusivity.

The → diffusion coefficient for a magnetic field. It is expressed as: η = 1/(μ₀σ), where μ₀ is the
→ magnetic permeability and σ the
→ conductivity.

See also: → magnetic; → diffusivity.

In terrestrial magnetism, the angle that a → magnetic needle makes with the horizontal plane at any specific location. The angle of magnetic dip at the → magnetic poles of Earth is 90°. Also called → inclination and → dip.

See also: → magnetic; → dip.

In terrestrial magnetism, the angle that a → magnetic needle makes with the horizontal plane at any specific location. The angle of magnetic dip at the → magnetic poles of Earth is 90°. Also called → inclination and → dip.

See also: → magnetic; → dip.

A system that generates a → magnetic field in which the field is considered to result from two opposite poles, as in the north and south poles of a magnet, much as an → electric field originates from a positive and a negative charge in an → electric dipole. A loop carrying an electric current also acts as a magnetic dipole.
Magnetic dipoles experience a torque in the presence of magnetic fields. → dipole moment; → magnetic moment.

See also: → magnetic; → dipole.

A system that generates a → magnetic field in which the field is considered to result from two opposite poles, as in the north and south poles of a magnet, much as an → electric field originates from a positive and a negative charge in an → electric dipole. A loop carrying an electric current also acts as a magnetic dipole.
Magnetic dipoles experience a torque in the presence of magnetic fields. → dipole moment; → magnetic moment.

See also: → magnetic; → dipole.

Same as → magnetic moment.

See also: → magnetic; → dipole; → moment.

Same as → magnetic moment.

See also: → magnetic; → dipole; → moment.

Any of several microscopic areas in a → ferromagnetic material that
possesses a net → magnetic field, because electron spins are aligned in the same direction.

In the absence of an external magnetic field, the directions of the magnetization vectors of the separate domains do not coincide and the resultant magnetization of the whole body may be zero.

See also: → magnetic; → domain.

Any of several microscopic areas in a → ferromagnetic material that
possesses a net → magnetic field, because electron spins are aligned in the same direction.

In the absence of an external magnetic field, the directions of the magnetization vectors of the separate domains do not coincide and the resultant magnetization of the whole body may be zero.

See also: → magnetic; → domain.

The energy stored in a magnetic field. It is the → work that must be done to establish a magnetic field in terms of the → magnetic induction. Magnetic energy varies as the square of the magnetic induction. It can be expressed in several other ways, for example in terms of the current and of the magnetic flux, or in terms of the current density and vector potential.

See also: → magnetic; → energy.

The energy stored in a magnetic field. It is the → work that must be done to establish a magnetic field in terms of the → magnetic induction. Magnetic energy varies as the square of the magnetic induction. It can be expressed in several other ways, for example in terms of the current and of the magnetic flux, or in terms of the current density and vector potential.

See also: → magnetic; → energy.

A field of force that is generated by electric currents, or, equivalently, a region in which magnetic forces can be observed.

See also: → magnetic; → field.

A field of force that is generated by electric currents, or, equivalently, a region in which magnetic forces can be observed.

See also: → magnetic; → field.

An imaginary line used for representing the strength and direction of a magnetic field. Charged particles move freely along magnetic field lines, but are inhibited by the magnetic force from moving across field lines.

See also: → magnetic; → field; → line.

An imaginary line used for representing the strength and direction of a magnetic field. Charged particles move freely along magnetic field lines, but are inhibited by the magnetic force from moving across field lines.

See also: → magnetic; → field; → line.

Same as → magnetic intensity.

See also: → magnetic; → field; → intensity.

Same as → magnetic intensity.

See also: → magnetic; → field; → intensity.

A measure of the quantity of magnetism or magnetic field. It is the number of lines of force passing normally through a given area. Magnetic flux is a scalar quantity defined as the surface integral of the → magnetic flux density. It is usually denoted by the Greek letter Φ and its SI unit is the → weber.

See also: → magnetic; → flux.

A measure of the quantity of magnetism or magnetic field. It is the number of lines of force passing normally through a given area. Magnetic flux is a scalar quantity defined as the surface integral of the → magnetic flux density. It is usually denoted by the Greek letter Φ and its SI unit is the → weber.

See also: → magnetic; → flux.

A vector quantity measuring the strength and direction of the magnetic field. It is the → magnetic flux per unit area of a magnetic field at right angles to the magnetic force. Magnetic flux density is expressed in → teslas. Also called → magnetic induction.

See also: → magnetic; → flux; → density.

A vector quantity measuring the strength and direction of the magnetic field. It is the → magnetic flux per unit area of a magnetic field at right angles to the magnetic force. Magnetic flux density is expressed in → teslas. Also called → magnetic induction.

See also: → magnetic; → flux; → density.

A quantity that measures the extent to which the magnetic field lines wrap and coil around each other. It is closely related to field line topology. Magnetic helicity is defined by: H_M = ∫ A . B dV, where A is the vector potential of the magnetic field and the integration is over a volume V. → helicity; → kinetic helicity

See also: → magnetic; → helicity.

A quantity that measures the extent to which the magnetic field lines wrap and coil around each other. It is closely related to field line topology. Magnetic helicity is defined by: H_M = ∫ A . B dV, where A is the vector potential of the magnetic field and the integration is over a volume V. → helicity; → kinetic helicity

See also: → magnetic; → helicity.

Same as → magnetic dip or → dip.

See also: → magnetic; → inclination.

Same as → magnetic dip or → dip.

See also: → magnetic; → inclination.

1. Same as → magnetic flux density.
   

2. The production of a magnetic field in a piece of un-magnetized iron or other → ferromagnetic substance when a magnet is brought near it.
   The magnet causes the individual particles of iron, which act like tiny magnets, to line up so that the sample as a whole becomes magnetized.

See also: → magnetic; → induction.

1. Same as → magnetic flux density.
   

2. The production of a magnetic field in a piece of un-magnetized iron or other → ferromagnetic substance when a magnet is brought near it.
   The magnet causes the individual particles of iron, which act like tiny magnets, to line up so that the sample as a whole becomes magnetized.

See also: → magnetic; → induction.

Strength of a magnetic field at a point, denoted H. The force which could be exerted on unit north magnetic pole situated at that point. Measured in oersteds. Same as → magnetic field strength.

See also: → magnetic; → intensity.

Strength of a magnetic field at a point, denoted H. The force which could be exerted on unit north magnetic pole situated at that point. Measured in oersteds. Same as → magnetic field strength.

See also: → magnetic; → intensity.

A → stellar magnetic field associated with a → massive star. Magnetic fields are detected only for seven to ten percent of all studied massive → OB stars, and the magnetic field occurrence does not depend on the → spectral type. Because these magnetic fields seem to be stable over long time-scales and their strength does not seem to correlate with known stellar properties, it is assumed that they are of fossil origin (→ fossil magnetic field) and are frozen into the → radiative envelope of the stars. The fields are those of the birth → molecular clouds, partly trapped inside the → pre-main sequence star during the cloud → collapse phase, possibly further enhanced by a → dynamo effect in the early fully convective stellar phase. Typically, the polar field strength ranges from about a hundred → Gauss up to several kiloGauss. However, some weaker fields, below 100 G, have recently been detected.

The stellar magnetic field influences many different regions of the star with various effects. In the deep interior of the star, the field influences the internal → mixing of the star and this affects the size of the → convective overshooting region, changing the lifetime of the star by decreasing the amount of fuel for nuclear burning. Magnetic stars can also confine their → stellar winds, due to their strong magnetic fields, into a → magnetosphere, which slows down the → rotational velocity of the star. This → magnetic braking is an efficient mechanism for → angular momentum transport. At the stellar surface, the magnetic fields can create and sustain areas of chemical over- or under-abundances and/or large temperature differences, which are called spots (Buysschaert et al., 2016, astro-ph/1709.02619).

See also: → magnetic; → massive; → star.

A → stellar magnetic field associated with a → massive star. Magnetic fields are detected only for seven to ten percent of all studied massive → OB stars, and the magnetic field occurrence does not depend on the → spectral type. Because these magnetic fields seem to be stable over long time-scales and their strength does not seem to correlate with known stellar properties, it is assumed that they are of fossil origin (→ fossil magnetic field) and are frozen into the → radiative envelope of the stars. The fields are those of the birth → molecular clouds, partly trapped inside the → pre-main sequence star during the cloud → collapse phase, possibly further enhanced by a → dynamo effect in the early fully convective stellar phase. Typically, the polar field strength ranges from about a hundred → Gauss up to several kiloGauss. However, some weaker fields, below 100 G, have recently been detected.

The stellar magnetic field influences many different regions of the star with various effects. In the deep interior of the star, the field influences the internal → mixing of the star and this affects the size of the → convective overshooting region, changing the lifetime of the star by decreasing the amount of fuel for nuclear burning. Magnetic stars can also confine their → stellar winds, due to their strong magnetic fields, into a → magnetosphere, which slows down the → rotational velocity of the star. This → magnetic braking is an efficient mechanism for → angular momentum transport. At the stellar surface, the magnetic fields can create and sustain areas of chemical over- or under-abundances and/or large temperature differences, which are called spots (Buysschaert et al., 2016, astro-ph/1709.02619).

See also: → magnetic; → massive; → star.

A meridian passing through the Earth’s → magnetic poles.

See also: → magnetic; → meridian.

A meridian passing through the Earth’s → magnetic poles.

See also: → magnetic; → meridian.

1. A measure of the strength of a magnet or current-carrying coil. In the case of a bar magnet it is obtained by multiplying the distance between the two magnetic poles by the average strength of the poles. Same as → magnetic dipole moment See also → dipole moment.
   

2. A measure of the magnetic flux set up by the gyration of an electric charge in a magnetic field.
   

3. In atomic and nuclear physics, → spin magnetic moment.

See also: → magnetic; → moment.

1. A measure of the strength of a magnet or current-carrying coil. In the case of a bar magnet it is obtained by multiplying the distance between the two magnetic poles by the average strength of the poles. Same as → magnetic dipole moment See also → dipole moment.
   

2. A measure of the magnetic flux set up by the gyration of an electric charge in a magnetic field.
   

3. In atomic and nuclear physics, → spin magnetic moment.

See also: → magnetic; → moment.

A hypothetical particle that carries a single → magnetic pole, in contrast to magnets which are north-south pole pairs.
These massive particles (billions of times heavier than the → proton) are required by grand unified theories(→ GUTs) to explain the actual matter content of the Universe, particularly the dominance of matter upon → antimatter. However, their existence contradicts → Gauss’s law for magnetism.

See also: → magnetic; → monopole.

A hypothetical particle that carries a single → magnetic pole, in contrast to magnets which are north-south pole pairs.
These massive particles (billions of times heavier than the → proton) are required by grand unified theories(→ GUTs) to explain the actual matter content of the Universe, particularly the dominance of matter upon → antimatter. However, their existence contradicts → Gauss’s law for magnetism.

See also: → magnetic; → monopole.

A problem concerning the compatibility of grand unified theories (→ GUTs) with standard cosmology. If standard cosmology was combined with grand unified theories, far too many → magnetic monopoles would have been produced in the early Universe. The → inflation hypothesis aims at
explaining the observed scarcity of monopoles. The inflation has deceased their density by a huge factor.

See also: → magnetic; → monopole; → problem.

A problem concerning the compatibility of grand unified theories (→ GUTs) with standard cosmology. If standard cosmology was combined with grand unified theories, far too many → magnetic monopoles would have been produced in the early Universe. The → inflation hypothesis aims at
explaining the observed scarcity of monopoles. The inflation has deceased their density by a huge factor.

See also: → magnetic; → monopole; → problem.

A slender → magnet suspended in a magnetic compass on a mounting with little friction; used to indicate the direction of the Earth’s → magnetic pole.

See also: → magnetic; → needle.

A slender → magnet suspended in a magnetic compass on a mounting with little friction; used to indicate the direction of the Earth’s → magnetic pole.

See also: → magnetic; → needle.

A point of the → magnetosphere where the Earth’s → magnetic field points vertically downward; in other words it has a 90° → magnetic dip toward the Earth’s surface. The magnetic north pole can also be defined as the point toward which the south pole of the → compass needle is directed. The magnetic north pole is different from the → geographic north pole. It is actually hundreds of kilometers south of the geographic north pole. However, this has not always been the case.

In the past 150 years it has moved more than 1,000 kilometers. Every 200,000 to 300,000 years the magnetic field of the Earth reverses direction, → magnetic reversal. Since the Earth’s magnetic field is not exactly symmetrical, the north and south magnetic poles are not → antipodal.

See also: → magnetic; → north; → pole.

A point of the → magnetosphere where the Earth’s → magnetic field points vertically downward; in other words it has a 90° → magnetic dip toward the Earth’s surface. The magnetic north pole can also be defined as the point toward which the south pole of the → compass needle is directed. The magnetic north pole is different from the → geographic north pole. It is actually hundreds of kilometers south of the geographic north pole. However, this has not always been the case.

In the past 150 years it has moved more than 1,000 kilometers. Every 200,000 to 300,000 years the magnetic field of the Earth reverses direction, → magnetic reversal. Since the Earth’s magnetic field is not exactly symmetrical, the north and south magnetic poles are not → antipodal.

See also: → magnetic; → north; → pole.

A region of the → solar corona where the → magnetic field vanishes.

See also: → magnetic; → null; → point.

A region of the → solar corona where the → magnetic field vanishes.

See also: → magnetic; → null; → point.

The ratio of the → magnetic induction, B, in the substance to the external magnetic field, H, causing the → induction: μ = B/H. It is measured in henry/meter and is known as absolute permeability. The relative permeability is equal to the ratio of absolute permeability to the permeability of the free space. Thus μ_r = μ/μ₀, where μ₀, the permeability of free space has the value 4π x 10^-7 henry/meter.

See also: → magnetic; → permeability.

The ratio of the → magnetic induction, B, in the substance to the external magnetic field, H, causing the → induction: μ = B/H. It is measured in henry/meter and is known as absolute permeability. The relative permeability is equal to the ratio of absolute permeability to the permeability of the free space. Thus μ_r = μ/μ₀, where μ₀, the permeability of free space has the value 4π x 10^-7 henry/meter.

See also: → magnetic; → permeability.

1. The region of a magnet toward which the lines of magnetic force
   converge (south pole) or from which the lines of force diverge (north pole).
   

2. Either of the two points on the Earth’s surface where the magnetic lines of force converge. They are not aligned with the geographical poles, but shift and do not lie exactly opposite of the other. → magnetic north pole, → magnetic south pole, → magnetic reversal.

See also: → magnetic; → pole.

1. The region of a magnet toward which the lines of magnetic force
   converge (south pole) or from which the lines of force diverge (north pole).
   

2. Either of the two points on the Earth’s surface where the magnetic lines of force converge. They are not aligned with the geographical poles, but shift and do not lie exactly opposite of the other. → magnetic north pole, → magnetic south pole, → magnetic reversal.

See also: → magnetic; → pole.

A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → kinematic viscosity to → magnetic diffusion. It is described by: P_r = σμ₀ν = ν/η, where σ is the → conductivity of the fluid, μ₀ is the → magnetic permeability of the fluid, ν is the kinematic viscosity of the fluid, and η is the → magnetic diffusivity.

See also: → magnetic; → Prandtl number.

A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → kinematic viscosity to → magnetic diffusion. It is described by: P_r = σμ₀ν = ν/η, where σ is the → conductivity of the fluid, μ₀ is the → magnetic permeability of the fluid, ν is the kinematic viscosity of the fluid, and η is the → magnetic diffusivity.

See also: → magnetic; → Prandtl number.

The pressure exerted by a magnetic field on the material that contains the field.

See also: → magnetic; → pressure.

The pressure exerted by a magnetic field on the material that contains the field.

See also: → magnetic; → pressure.

In atomic physics, a quantum number that denotes the energy levels available within a subshell. Designated by the letter m, it is one of a set of quantum numbers which describe the unique quantum state of an electron.

See also: → magnetic; → quantum;
→ number.

In atomic physics, a quantum number that denotes the energy levels available within a subshell. Designated by the letter m, it is one of a set of quantum numbers which describe the unique quantum state of an electron.

See also: → magnetic; → quantum;
→ number.

In a → plasma, a change of → magnetic connectivity of plasma elements due to the presence of a localized → diffusion region. It allows charged particles to move from one → magnetic field line to another. Magnetic reconnection is an important process transforming magnetic energy into heat or/and kinetic energy. Magnetic reconnection events occur in the Earth’s → magnetosphere. The process plays an important role in explosive phenomena in the Sun, such as → coronal mass ejections and
→ solar flares which heat the → solar corona.

See also: → magnetic; → re-; → connection.

In a → plasma, a change of → magnetic connectivity of plasma elements due to the presence of a localized → diffusion region. It allows charged particles to move from one → magnetic field line to another. Magnetic reconnection is an important process transforming magnetic energy into heat or/and kinetic energy. Magnetic reconnection events occur in the Earth’s → magnetosphere. The process plays an important role in explosive phenomena in the Sun, such as → coronal mass ejections and
→ solar flares which heat the → solar corona.

See also: → magnetic; → re-; → connection.

The process by which a magnetic system relaxes to its minimum energy state over time.

See also: → magnetic; → relaxation.

The process by which a magnetic system relaxes to its minimum energy state over time.

See also: → magnetic; → relaxation.

A phenomenon exhibited by certain atoms whereby they absorb energy at specific (resonant) frequencies when subjected to alternating magnetic fields.

See also: → magnetic; → resonance.

A phenomenon exhibited by certain atoms whereby they absorb energy at specific (resonant) frequencies when subjected to alternating magnetic fields.

See also: → magnetic; → resonance.

A change in the Earth’s → magnetic field in which the → magnetic north pole is transformed into a → magnetic south pole and the magnetic south pole becomes a magnetic north pole. There are geological proofs indicating that the Earth’s magnetic field has undergone numerous reversals of → polarity in the past.

In the last 10 million years, there have been, on average, 4 or 5 reversals per million years. At other times, for example during the → Cretaceous era, there have been much longer periods when no reversals occurred.

Over the past two centuries, Earth’s magnetic field has weakened by 15%. Risks of a weak magnetic field include more deaths from cancer due to increased radiation, electrical grid collapse from severe solar storms, climate change, and temporary ozone holes. See also → geomagnetic excursion.

See also: → magnetic; → reversal.

A change in the Earth’s → magnetic field in which the → magnetic north pole is transformed into a → magnetic south pole and the magnetic south pole becomes a magnetic north pole. There are geological proofs indicating that the Earth’s magnetic field has undergone numerous reversals of → polarity in the past.

In the last 10 million years, there have been, on average, 4 or 5 reversals per million years. At other times, for example during the → Cretaceous era, there have been much longer periods when no reversals occurred.

Over the past two centuries, Earth’s magnetic field has weakened by 15%. Risks of a weak magnetic field include more deaths from cancer due to increased radiation, electrical grid collapse from severe solar storms, climate change, and temporary ozone holes. See also → geomagnetic excursion.

See also: → magnetic; → reversal.

A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of
→ magnetic advection to → magnetic diffusion. It is given by:

R_m = σμ₀νLU₀,

where σ is the → conductivity of the fluid, μ₀ is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and
U₀ the characteristic velocity of the flow. A typical value for the Earth is R_m ~ 200.

See also: → magnetic; → Reynolds number.

A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of
→ magnetic advection to → magnetic diffusion. It is given by:

R_m = σμ₀νLU₀,

where σ is the → conductivity of the fluid, μ₀ is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and
U₀ the characteristic velocity of the flow. A typical value for the Earth is R_m ~ 200.

See also: → magnetic; → Reynolds number.

In → plasma physics, a → quantity that describes the → resistance of a → charged particle to change its direction of motion under the influence of a perpendicular → magnetic field. Rigidity is defined as: R = r_LBc = (pc)/(Ze), where r_L is the → Larmor radius, B is
→ magnetic induction, c is the → speed of light, p is the → momentum of the particle, Z is → atomic number, and e the → electron charge. Since pc has the dimensions of energy and e the dimensions of charge, rigidity has the dimensions of → volts (a 10 GeV proton has a rigidity of 10 GV). In → cosmic ray studies, the energies of cosmic rays are often quoted in terms of their rigidities, rather than their energies per nucleon.

See also: → magnetic; → rigidity.

In → plasma physics, a → quantity that describes the → resistance of a → charged particle to change its direction of motion under the influence of a perpendicular → magnetic field. Rigidity is defined as: R = r_LBc = (pc)/(Ze), where r_L is the → Larmor radius, B is
→ magnetic induction, c is the → speed of light, p is the → momentum of the particle, Z is → atomic number, and e the → electron charge. Since pc has the dimensions of energy and e the dimensions of charge, rigidity has the dimensions of → volts (a 10 GeV proton has a rigidity of 10 GV). In → cosmic ray studies, the energies of cosmic rays are often quoted in terms of their rigidities, rather than their energies per nucleon.

See also: → magnetic; → rigidity.

The → counterpart of the → magnetic north pole. It lies near the → geographic north pole.

See also: → magnetic; → south; → pole.

The → counterpart of the → magnetic north pole. It lies near the → geographic north pole.

See also: → magnetic; → south; → pole.

A process whereby the (internal) → magnetic field of a star modifies the → pulsations by lifting some of its degeneracy. Instead of just one pulsation frequency, a multiplet of frequencies is then observed. This effect was proposed as a possible explanation for the observed frequency pattern of → Beta Cephei. In practice, the magnetic splitting is difficult to observe, because of the very small expected frequency difference between the peaks. However, when unaccounted for, it may lead to a wrong mode identification. The current best candidate to detect magnetic splitting is → HD 43317, since this star displays two close frequency patterns (Buysschaert et al., 2017, astro-ph/1709.02619).

See also: → magnetic; → splitting.

A process whereby the (internal) → magnetic field of a star modifies the → pulsations by lifting some of its degeneracy. Instead of just one pulsation frequency, a multiplet of frequencies is then observed. This effect was proposed as a possible explanation for the observed frequency pattern of → Beta Cephei. In practice, the magnetic splitting is difficult to observe, because of the very small expected frequency difference between the peaks. However, when unaccounted for, it may lead to a wrong mode identification. The current best candidate to detect magnetic splitting is → HD 43317, since this star displays two close frequency patterns (Buysschaert et al., 2017, astro-ph/1709.02619).

See also: → magnetic; → splitting.

A star whose → spectral lines show the → Zeeman effect. See also: → stellar magnetic field, → magnetic massive star, → Ap/Bp star.

See also: → magnetic; → star.

A star whose → spectral lines show the → Zeeman effect. See also: → stellar magnetic field, → magnetic massive star, → Ap/Bp star.

See also: → magnetic; → star.

A temporary, worldwide disturbance of the Earth’s magnetic field by streams of charged particles from the Sun. Magnetic storms are frequently characterized by a sudden onset, in which the magnetic field undergoes marked changes in the course of an hour or less, followed by a very gradual return to normalcy, which may take several days.

See also: → magnetic; → storm.

A temporary, worldwide disturbance of the Earth’s magnetic field by streams of charged particles from the Sun. Magnetic storms are frequently characterized by a sudden onset, in which the magnetic field undergoes marked changes in the course of an hour or less, followed by a very gradual return to normalcy, which may take several days.

See also: → magnetic; → storm.

A property of material defined by the ratio of the → magnetization to the → magnetic intensity. In other words, the magnetization per unit magnetic intensity.

See also: → magnetic; → susceptibility.

A property of material defined by the ratio of the → magnetization to the → magnetic intensity. In other words, the magnetization per unit magnetic intensity.

See also: → magnetic; → susceptibility.

A continuous, flexible ribbon impregnated or coated with magnetic-sensitive material on which information (sound, images, data, etc.) may be recorded.

See also: → magnetic; → tape.

A continuous, flexible ribbon impregnated or coated with magnetic-sensitive material on which information (sound, images, data, etc.) may be recorded.

See also: → magnetic; → tape.

In → magnetohydrodynamic (MHD) treatment of → plasmas, that component of the → Lorentz force which is directed toward the centre of curvature of the → magnetic field lines and thus acts to straighten out the field lines.

The Lorentz force can be decomposed into two components orthogonal to the magnetic field:

j× B = (B . ∇) B / μ₀

• ∇ (B² / 2μ₀),

where j is the → current density, μ₀ is the → magnetic permeability of free space, and B is the → magnetic flux density. The left side term is the Lorentz force, the first term on the right side is the magnetic tension and the second term the → magnetic pressure.

See also: → magnetic; → tension.

In → magnetohydrodynamic (MHD) treatment of → plasmas, that component of the → Lorentz force which is directed toward the centre of curvature of the → magnetic field lines and thus acts to straighten out the field lines.

The Lorentz force can be decomposed into two components orthogonal to the magnetic field:

j× B = (B . ∇) B / μ₀

• ∇ (B² / 2μ₀),

where j is the → current density, μ₀ is the → magnetic permeability of free space, and B is the → magnetic flux density. The left side term is the Lorentz force, the first term on the right side is the magnetic tension and the second term the → magnetic pressure.

See also: → magnetic; → tension.

A vector field A defined so that the → magnetic field  B is given by its → curl: B = ∇ x A.

See also: → magnetic; → vector; → potential.

A vector field A defined so that the → magnetic field  B is given by its → curl: B = ∇ x A.

See also: → magnetic; → vector; → potential.

Radiation emitted by a rotating magnet.

See also: → magnetic; → dipole;
→ radiation.

Radiation emitted by a rotating magnet.

See also: → magnetic; → dipole;
→ radiation.

The study of magnetic phenomena, comprising magnetostatics and electromagnetism.

See also: → magnetic; → -ics.

The study of magnetic phenomena, comprising magnetostatics and electromagnetism.

See also: → magnetic; → -ics.

The science of magnetic phenomena, including the fields and forces produced by magnets and, more generally, by moving electric charges.

See also: N.L. magnetismus; → magnet + → -ism.

The science of magnetic phenomena, including the fields and forces produced by magnets and, more generally, by moving electric charges.

See also: N.L. magnetismus; → magnet + → -ism.

An international collaboration devoted to the study of the origin and physics of → magnetic fields in → massive stars. The project uses several observatories and a large number of telescopes equipped with → spectropolarimetric and → asteroseismologic instruments, including → HARPS, → HARPSpol, and → ESPaDOnS (Wade et al., 2016, MNRAS 456, 2).

See also: → magnetism; → massive; → star.

An international collaboration devoted to the study of the origin and physics of → magnetic fields in → massive stars. The project uses several observatories and a large number of telescopes equipped with → spectropolarimetric and → asteroseismologic instruments, including → HARPS, → HARPSpol, and → ESPaDOnS (Wade et al., 2016, MNRAS 456, 2).

See also: → magnetism; → massive; → star.

1. General: The process of magnetizing or the state of being magnetized.
   

2. Electricity: The → magnetic moment per unit volume induced by an external magnetic field; measured in → amperes per meter.

See also: Verbal noun of → magnetize.

1. General: The process of magnetizing or the state of being magnetized.
   

2. Electricity: The → magnetic moment per unit volume induced by an external magnetic field; measured in → amperes per meter.

See also: Verbal noun of → magnetize.

To make a magnet of, or impart the properties of a magnet to.

See also: From → magnet + → -ize.

To make a magnet of, or impart the properties of a magnet to.

See also: From → magnet + → -ize.

Having been made magnetic; magnetic properties imparted to.

See also: Past participle of → magnetize.

Having been made magnetic; magnetic properties imparted to.

See also: Past participle of → magnetize.

A plasma containing a magnetic field which is strong enough to change the path of charged particles. It can be a → collisional plasma or → noncollisional plasma.

See also: → magnetized; → plasma.

A plasma containing a magnetic field which is strong enough to change the path of charged particles. It can be a → collisional plasma or → noncollisional plasma.

See also: → magnetized; → plasma.

Empty space influenced by very strong → magnetic field. Same as → birefringent vacuum.

See also: → magnetized; → vacuum.

Empty space influenced by very strong → magnetic field. Same as → birefringent vacuum.

See also: → magnetized; → vacuum.

The prefix form of → magnet, representing magnetic or magnetism
in compound words, such as → magnetogram, → magnetohydrodynamics.

See also: → magnet.

The prefix form of → magnet, representing magnetic or magnetism
in compound words, such as → magnetogram, → magnetohydrodynamics.

See also: → magnet.

Combined study of the large-scale → magnetic field (→ magnetometry) and → stellar pulsations
(→ asteroseismology). Magneto-asteroseismology provides strong complementary diagnostics suitable for detailed stellar modeling and permits the determination of the → internal structure and conditions within → magnetic massive  → pulsators, for example the effect of magnetism on → mixing processes. More specifically, asteroseismology yields information on the → density, → composition, and → chemical mixing in multiple internal layers (depending on the number of studied frequencies). Additionally, when rotationally split pulsation modes are observed, the internal rotation profile can be retrieved. From magnetometry surface properties are determined, related to the → chemical composition, including → starspots, and the magnetic field, such as its geometry, obliquity, and strength. Magnetic studies also provide constraints about the → stellar wind geometry and the → circumstellar environment. Moreover, the stellar → rotation period period and the → angle of inclination toward the observer are also retrieved (Buysschaert et al., 2017, astro-ph/1709.02619).

See also: → magneto-; → asteroseismology.

Combined study of the large-scale → magnetic field (→ magnetometry) and → stellar pulsations
(→ asteroseismology). Magneto-asteroseismology provides strong complementary diagnostics suitable for detailed stellar modeling and permits the determination of the → internal structure and conditions within → magnetic massive  → pulsators, for example the effect of magnetism on → mixing processes. More specifically, asteroseismology yields information on the → density, → composition, and → chemical mixing in multiple internal layers (depending on the number of studied frequencies). Additionally, when rotationally split pulsation modes are observed, the internal rotation profile can be retrieved. From magnetometry surface properties are determined, related to the → chemical composition, including → starspots, and the magnetic field, such as its geometry, obliquity, and strength. Magnetic studies also provide constraints about the → stellar wind geometry and the → circumstellar environment. Moreover, the stellar → rotation period period and the → angle of inclination toward the observer are also retrieved (Buysschaert et al., 2017, astro-ph/1709.02619).

See also: → magneto-; → asteroseismology.

The acceleration exerted on the plasma particles according to the → magnetocentrifugal model.

See also: → magnetocentrifugal model; → acceleration.

The acceleration exerted on the plasma particles according to the → magnetocentrifugal model.

See also: → magnetocentrifugal model; → acceleration.

A → magnetohydrodynamic model devised to account for the → bipolar jets and → outflows observed around → protostars. Basically, a → poloidal magnetic field is frozen into a rotating → accretion disk. If the angle between the magnetic field lines threading the disk and the rotation axis of the disk is larger than 30°,
the plasma can be accelerated out of the accretion disk along the field lines. The field lines rotate at a constant → angular velocity, and as the gas moves outward along the field lines, it is accelerated by an increasing → centrifugal force (magnetocentrifugal acceleration). At some point, when the rotation velocity is about the same as the → Alfven velocity in the gas, the field lines get increasingly wound up by the inertia of the attached gas and a strong → toroidal magnetic field component is generated. The toroidal component is the main agent in collimating the flow into a direction along the → open magnetic field lines. The earliest version of the model was proposed by Blandford & Payne (1982, MNRAS 199, 883). It has two main versions: → X-wind and → disk wind models.
See also → magnetorotational instability.

See also: → magneto-; → centrifugal; → model.

A → magnetohydrodynamic model devised to account for the → bipolar jets and → outflows observed around → protostars. Basically, a → poloidal magnetic field is frozen into a rotating → accretion disk. If the angle between the magnetic field lines threading the disk and the rotation axis of the disk is larger than 30°,
the plasma can be accelerated out of the accretion disk along the field lines. The field lines rotate at a constant → angular velocity, and as the gas moves outward along the field lines, it is accelerated by an increasing → centrifugal force (magnetocentrifugal acceleration). At some point, when the rotation velocity is about the same as the → Alfven velocity in the gas, the field lines get increasingly wound up by the inertia of the attached gas and a strong → toroidal magnetic field component is generated. The toroidal component is the main agent in collimating the flow into a direction along the → open magnetic field lines. The earliest version of the model was proposed by Blandford & Payne (1982, MNRAS 199, 883). It has two main versions: → X-wind and → disk wind models.
See also → magnetorotational instability.

See also: → magneto-; → centrifugal; → model.

A graphic representation of solar magnetic field strengths and polarity.

See also: From → magneto- + → -gram.

A graphic representation of solar magnetic field strengths and polarity.

See also: From → magneto- + → -gram.

Of or relating to → magnetohydrodynamics.

See also: → magneto- + → hydrodynamic.

Of or relating to → magnetohydrodynamics.

See also: → magneto- + → hydrodynamic.

The dynamics of an ionized plasma in the non-relativistic, collisional case. In this description, charge oscillations and high frequency electromagnetic waves are neglected. It is an important field of astrophysics since plasma is one of the commonest forms of matter in the Universe, occurring in stars, planetary magnetospheres, and interplanetary and interstellar space.

See also: From → magneto- + → hydrodynamics.

The dynamics of an ionized plasma in the non-relativistic, collisional case. In this description, charge oscillations and high frequency electromagnetic waves are neglected. It is an important field of astrophysics since plasma is one of the commonest forms of matter in the Universe, occurring in stars, planetary magnetospheres, and interplanetary and interstellar space.

See also: From → magneto- + → hydrodynamics.

Any of a variety of devices used to measure the strength and direction of a magnetic field.

See also: From → magneto- + → -meter.

Any of a variety of devices used to measure the strength and direction of a magnetic field.

See also: From → magneto- + → -meter.

The detection or measurement of a magnetic field, especially its strength and direction. See also → magnetometer.

See also: → magneto-; → -metry.

The detection or measurement of a magnetic field, especially its strength and direction. See also → magnetometer.

See also: → magneto-; → -metry.

Fundamental constant, first calculated by Bohr, for the intrinsic magnetic moment of an electron. → Bohr magneton.

See also: From → magnet + → -on.

Fundamental constant, first calculated by Bohr, for the intrinsic magnetic moment of an electron. → Bohr magneton.

See also: From → magnet + → -on.

The boundary layer between a planet’s → magnetosphere and the → magnetic field of the → solar wind. It borders the → magnetosheath and is defined by the surface on which the pressure of the solar wind is balanced by that of the planet’s magnetic field. The front point of the Earth’s magnetopause, on the sun-ward side of the Earth, is about 10 terrestrial radii, on average. This point
can be closer or farther, because the magnetopause contracts or expands depending on the intensity of the solar wind.

Etymology (EN): From → magneto- + pause “break, cessation, stop,” from M.Fr. pause, from L. pausa “a halt, stop, cessation,” from Gk. pausis “stopping, ceasing,” from pauein “to stop, to cause to cease.”

Etymology (PE): From meqnât-→ magnet + marz “frontier, border, boundary,” from Mid.Pers. marz “boundary;” Av. marəza- “border, district,” marəz- “to rub, wipe;” Mod.Pers. parmâs “contact, touching” (→ contact), mâl-, mâlidan “to rub;” PIE base *merg- “boundary, border;” cf. L. margo “edge” (Fr. marge “margin”); Ger. Mark; E. mark, margin.

The boundary layer between a planet’s → magnetosphere and the → magnetic field of the → solar wind. It borders the → magnetosheath and is defined by the surface on which the pressure of the solar wind is balanced by that of the planet’s magnetic field. The front point of the Earth’s magnetopause, on the sun-ward side of the Earth, is about 10 terrestrial radii, on average. This point
can be closer or farther, because the magnetopause contracts or expands depending on the intensity of the solar wind.

Etymology (EN): From → magneto- + pause “break, cessation, stop,” from M.Fr. pause, from L. pausa “a halt, stop, cessation,” from Gk. pausis “stopping, ceasing,” from pauein “to stop, to cause to cease.”

Etymology (PE): From meqnât-→ magnet + marz “frontier, border, boundary,” from Mid.Pers. marz “boundary;” Av. marəza- “border, district,” marəz- “to rub, wipe;” Mod.Pers. parmâs “contact, touching” (→ contact), mâl-, mâlidan “to rub;” PIE base *merg- “boundary, border;” cf. L. margo “edge” (Fr. marge “margin”); Ger. Mark; E. mark, margin.

An instability that arises from the action of a weak → poloidal magnetic field in a → differentially rotating system, such as a → Keplerian disk. The MRI provides a mechanism to account for the additional outward → angular momentum transport.
To put it simply, the → frozen magnetic field line
acts as a spring connecting two radially neighboring fluid parcels. In a Keplerian disk the inner fluid parcel orbits more rapidly than the outer, causing the spring to stretch. The magnetic tension forces the inner parcel to slow down reducing its angular momentum by moving it to a lower orbit. The outer fluid parcel is forced by the spring to speed up, increase its angular momentum, and therefore move to a higher orbit. The spring tension increases as the two fluid parcels grow further apart, and eventually the process runs away. The MRI was first noted in a non-astrophysical context by E. Velikhov in 1959 when considering the stability of → Couette flow of an ideal hydromagnetic fluid. His result was later generalized by S. Chandrasekhar in 1960. The MRI was rediscovered by Balbus and Hawley 1991 (ApJ 376, 214) who demonstrated that this instability does indeed manifest itself in → accretion disks, and could account for the turbulent mixing needed to explain the observed mass → accretion rates.

See also: → magneto-; → rotational; → instability.

An instability that arises from the action of a weak → poloidal magnetic field in a → differentially rotating system, such as a → Keplerian disk. The MRI provides a mechanism to account for the additional outward → angular momentum transport.
To put it simply, the → frozen magnetic field line
acts as a spring connecting two radially neighboring fluid parcels. In a Keplerian disk the inner fluid parcel orbits more rapidly than the outer, causing the spring to stretch. The magnetic tension forces the inner parcel to slow down reducing its angular momentum by moving it to a lower orbit. The outer fluid parcel is forced by the spring to speed up, increase its angular momentum, and therefore move to a higher orbit. The spring tension increases as the two fluid parcels grow further apart, and eventually the process runs away. The MRI was first noted in a non-astrophysical context by E. Velikhov in 1959 when considering the stability of → Couette flow of an ideal hydromagnetic fluid. His result was later generalized by S. Chandrasekhar in 1960. The MRI was rediscovered by Balbus and Hawley 1991 (ApJ 376, 214) who demonstrated that this instability does indeed manifest itself in → accretion disks, and could account for the turbulent mixing needed to explain the observed mass → accretion rates.

See also: → magneto-; → rotational; → instability.

The region between a planet’s magnetopause and the bow shock caused by the solar wind.

Etymology (EN): From → magneto- + sheath, from O.E. sceað, scæð, from P.Gmc. *skaithiz (cf. M.Du. schede, Du. schede, O.H.G. skaida, Ger. Scheide “scabbard”).

Etymology (PE): From meqnât-, → magnet, + niyâm “sheath,” from Proto-Iranian *nigāma-, from ni- “down; into,” → ni-, + gāma- “to go, to come” (Av. gam- “to come; to go,” jamaiti “goes;” O.Pers. gam- “to come; to go;” Mod./Mid.Pers. gâm
“step, pace,” âmadan “to come;” cf. Skt. gamati “goes;” Gk. bainein “to go, walk, step;” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE root *gwem- “to go, come”); cf. Skt. nigamá- “insertion, incorporation.”

The region between a planet’s magnetopause and the bow shock caused by the solar wind.

Etymology (EN): From → magneto- + sheath, from O.E. sceað, scæð, from P.Gmc. *skaithiz (cf. M.Du. schede, Du. schede, O.H.G. skaida, Ger. Scheide “scabbard”).

Etymology (PE): From meqnât-, → magnet, + niyâm “sheath,” from Proto-Iranian *nigāma-, from ni- “down; into,” → ni-, + gāma- “to go, to come” (Av. gam- “to come; to go,” jamaiti “goes;” O.Pers. gam- “to come; to go;” Mod./Mid.Pers. gâm
“step, pace,” âmadan “to come;” cf. Skt. gamati “goes;” Gk. bainein “to go, walk, step;” L. venire “to come;” Tocharian A käm- “to come;” O.H.G. queman “to come;” E. come; PIE root *gwem- “to go, come”); cf. Skt. nigamá- “insertion, incorporation.”

The region around a celestial body in which the magnetic field of the body dominates the external magnetic field. Each planet with a magnetic field (Earth, Jupiter, Saturn, Uranus, and Neptune) has a magnetopause.
The Earth’s magnetosphere is a dynamic system that responds to solar variations. It prevents most of the charged particles carried in the → solar wind, from hitting the Earth.
Since the solar wind is → supersonic, a → bow shock is formed on the sunward side of the magnetosphere. The solar wind ahead is deflected at a boundary called → magnetopause. The region between the bow shock and the magnetopause is called the → magnetosheath. As the solar wind sweeps past the Earth, the terrestrial magnetic field lines are stretched out toward the night side to form a → magnetotail.

See also: From → magnet + → sphere.

The region around a celestial body in which the magnetic field of the body dominates the external magnetic field. Each planet with a magnetic field (Earth, Jupiter, Saturn, Uranus, and Neptune) has a magnetopause.
The Earth’s magnetosphere is a dynamic system that responds to solar variations. It prevents most of the charged particles carried in the → solar wind, from hitting the Earth.
Since the solar wind is → supersonic, a → bow shock is formed on the sunward side of the magnetosphere. The solar wind ahead is deflected at a boundary called → magnetopause. The region between the bow shock and the magnetopause is called the → magnetosheath. As the solar wind sweeps past the Earth, the terrestrial magnetic field lines are stretched out toward the night side to form a → magnetotail.

See also: From → magnet + → sphere.

The portion of a planet’s → magnetosphere which is pushed away from the Sun by the solar wind. Earth’s magnetosphere extends about 65,000 km on the day-side but more than 10 times further.

See also: From → magneto- + → tail.

The portion of a planet’s → magnetosphere which is pushed away from the Sun by the solar wind. Earth’s magnetosphere extends about 65,000 km on the day-side but more than 10 times further.

See also: From → magneto- + → tail.

The factor by which the angular diameter of an object is apparently increased when viewed through an optical instrument to that of the object viewed by the unaided eye.

See also: Verbal noun of → magnify.

The factor by which the angular diameter of an object is apparently increased when viewed through an optical instrument to that of the object viewed by the unaided eye.

See also: Verbal noun of → magnify.

A thing or device that magnifies.

Etymology (EN): From → magnify + suffix -ir.

Etymology (PE): Bozognemâ, agent noun of bozorg nemudan, → magnify.

A thing or device that magnifies.

Etymology (EN): From → magnify + suffix -ir.

Etymology (PE): Bozognemâ, agent noun of bozorg nemudan, → magnify.

To increase the apparent size of, as a lens does.

Etymology (EN): From O.Fr. magnifier, from L. magnificare “esteem greatly, extol,” from magnificus “splendid,” from magnus “great” + root of facere “to make.”

Etymology (PE): From bozorg “large, magnificent, great” + nemudan “to show.” The first element from Mid.Pers. vazurg “great, big, high, lofty;” O.Pers. vazarka- “great;” Av. vazra- “club, mace” (Mod.Pers. gorz “mace”); cf. Skt. vájra- “(Indra’s) thunderbolt,” vaja- “strength, speed;” L. vigere “be lively, thrive,” velox “fast, lively,” vegere “to enliven,” vigil “watchful, awake;”
P.Gmc. *waken (Du. waken; O.H.G. wahhen; Ger. wachen “to be awake;” E. wake); PIE base *weg- “to be strong, be lively.” The second element nemudan from Mid.Pers. nimūdan, nimây- “to show,” from O.Pers./Av. ni- “down; into,” → ni-, + māy- “to measure,” → display.
Bozorgidan infinitive from bozorg + -idan.

To increase the apparent size of, as a lens does.

Etymology (EN): From O.Fr. magnifier, from L. magnificare “esteem greatly, extol,” from magnificus “splendid,” from magnus “great” + root of facere “to make.”

Etymology (PE): From bozorg “large, magnificent, great” + nemudan “to show.” The first element from Mid.Pers. vazurg “great, big, high, lofty;” O.Pers. vazarka- “great;” Av. vazra- “club, mace” (Mod.Pers. gorz “mace”); cf. Skt. vájra- “(Indra’s) thunderbolt,” vaja- “strength, speed;” L. vigere “be lively, thrive,” velox “fast, lively,” vegere “to enliven,” vigil “watchful, awake;”
P.Gmc. *waken (Du. waken; O.H.G. wahhen; Ger. wachen “to be awake;” E. wake); PIE base *weg- “to be strong, be lively.” The second element nemudan from Mid.Pers. nimūdan, nimây- “to show,” from O.Pers./Av. ni- “down; into,” → ni-, + māy- “to measure,” → display.
Bozorgidan infinitive from bozorg + -idan.

A lens or lens system that produces an enlarged virtual image of an object placed near its front focal point. According to Enoch (1998, SPIE vol. 3299, p. 424), the earliest lenses identified are from the IV/V Dynasties of Egypt,
dating back to about 4,500 years ago (e.g., the eyes of the Louvre statue Le scribe accroupi
and other examples located in the Cairo Museum). For more information see → burning sphere.

Etymology (EN): Magnifying, verbal adj. of → magnify; → glass.

Etymology (PE): Zarrebin, from zarré “a minute thing,” → particle,

• bin “seer; to see” (present stem of didan;
  Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
  Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see”).

A lens or lens system that produces an enlarged virtual image of an object placed near its front focal point. According to Enoch (1998, SPIE vol. 3299, p. 424), the earliest lenses identified are from the IV/V Dynasties of Egypt,
dating back to about 4,500 years ago (e.g., the eyes of the Louvre statue Le scribe accroupi
and other examples located in the Cairo Museum). For more information see → burning sphere.

Etymology (EN): Magnifying, verbal adj. of → magnify; → glass.

Etymology (PE): Zarrebin, from zarré “a minute thing,” → particle,

• bin “seer; to see” (present stem of didan;
  Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
  Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see”).

The ratio between the focal lengths of the objective and ocular in a telescope.

See also: Magnifying, verbal adj. of → magnify; → power.

The ratio between the focal lengths of the objective and ocular in a telescope.

See also: Magnifying, verbal adj. of → magnify; → power.

A measure of brightness in astronomy on a → logarithmic scale in which a difference of five magnitudes represents a difference of 100 times in brightness. In this scale the lower a magnitude, the brighter the object. The faintest magnitude reached by → unaided eye is 6.

Etymology (EN): From L. magnitudo “greatness, bulk, size,” from magnus “great,” cognate with Pers. meh “great, large” (Mid.Pers. meh, mas; Av. maz-, masan-, mazant- “great, important,” mazan- “greatness, majesty,” mazišta- “greatest;” cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- “great”) + -tudo, suffix forming abstract nouns from adjectives and participles.

Etymology (PE): Borz “height, magnitude” (it occurs also in the name of the mountain chain Alborz), related to boland “high,” bâlâ “up, above, high, elevated, height,” berg “mountain, hill” (Mid.Pers. buland “high;” O.Pers. baršan- “height;” Av. barəz- “high, mount,” barezan- “height;” cf. Skt. bhrant- “high;” L. fortis “strong” (Fr. & E. force); O.E. burg, burh “castle, fortified place,” from P.Gmc. *burgs “fortress;” Ger. Burg “castle,” Goth. baurgs “city,” E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg); PIE base *bhergh- “high”). Qadr, from Ar.

A measure of brightness in astronomy on a → logarithmic scale in which a difference of five magnitudes represents a difference of 100 times in brightness. In this scale the lower a magnitude, the brighter the object. The faintest magnitude reached by → unaided eye is 6.

Etymology (EN): From L. magnitudo “greatness, bulk, size,” from magnus “great,” cognate with Pers. meh “great, large” (Mid.Pers. meh, mas; Av. maz-, masan-, mazant- “great, important,” mazan- “greatness, majesty,” mazišta- “greatest;” cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- “great”) + -tudo, suffix forming abstract nouns from adjectives and participles.

Etymology (PE): Borz “height, magnitude” (it occurs also in the name of the mountain chain Alborz), related to boland “high,” bâlâ “up, above, high, elevated, height,” berg “mountain, hill” (Mid.Pers. buland “high;” O.Pers. baršan- “height;” Av. barəz- “high, mount,” barezan- “height;” cf. Skt. bhrant- “high;” L. fortis “strong” (Fr. & E. force); O.E. burg, burh “castle, fortified place,” from P.Gmc. *burgs “fortress;” Ger. Burg “castle,” Goth. baurgs “city,” E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg); PIE base *bhergh- “high”). Qadr, from Ar.

A scale for measuring and comparing the brightness of astronomical objects.

See also: → magnitude; → scale.

A scale for measuring and comparing the brightness of astronomical objects.

See also: → magnitude; → scale.

A survey in which the observed objects are bighter than a given → apparent magnitude.

See also: → magnitude; → limited; → volume.

A survey in which the observed objects are bighter than a given → apparent magnitude.

See also: → magnitude; → limited; → volume.

The force exerted on a spinning object moving through a fluid medium in virtue of → Bernoulli’s theorem. The Magnus force can deviate a football from its path when a player strikes it so that it spins about an axis perpendicular to the flow of air around it.
As the spinning ball moves through the air, it will create a pressure difference between its two sides. The air travels faster relative to the centre of the ball where its periphery is moving in the same direction as the airflow. This reduces the pressure according Bernoulli’s theorem. The opposite effect happens on the other side of the ball, where the air travels slower relative to the centre of the ball. There is therefore an imbalance in the forces
that will curve the ball’s trajectory.

See also: Named after Heinrich Gustav Magnus (1802-1870), a German chemist and physicist; → force.

The force exerted on a spinning object moving through a fluid medium in virtue of → Bernoulli’s theorem. The Magnus force can deviate a football from its path when a player strikes it so that it spins about an axis perpendicular to the flow of air around it.
As the spinning ball moves through the air, it will create a pressure difference between its two sides. The air travels faster relative to the centre of the ball where its periphery is moving in the same direction as the airflow. This reduces the pressure according Bernoulli’s theorem. The opposite effect happens on the other side of the ball, where the air travels slower relative to the centre of the ball. There is therefore an imbalance in the forces
that will curve the ball’s trajectory.

See also: Named after Heinrich Gustav Magnus (1802-1870), a German chemist and physicist; → force.

Any of various passerine birds of the genus Pica, especially Pica pica, having a black-and-white plumage, long tail, and a chattering call (Ditionary.com).

Etymology (EN): From Mag diminutive of Margaret, used to signify an excessively talkative person + pie the earlier name of the bird, from O.Fr. pie, from L. pica “magpie,” feminine of picus “woodpecker.”

Etymology (PE): Kaliž, variant of (Dehxodâ) kalâžé, kalâcé, qalivâš, qalivâj,
(Qäyen, Gonâbâd) kaliždak, (Xorâsâni) kelidjak, (Dari Yazd) kelociri, (Bardesir) kerâcik, related to kalâq + dimunitive suffix -iž, vaeiants -iz, -ak.

Any of various passerine birds of the genus Pica, especially Pica pica, having a black-and-white plumage, long tail, and a chattering call (Ditionary.com).

Etymology (EN): From Mag diminutive of Margaret, used to signify an excessively talkative person + pie the earlier name of the bird, from O.Fr. pie, from L. pica “magpie,” feminine of picus “woodpecker.”

Etymology (PE): Kaliž, variant of (Dehxodâ) kalâžé, kalâcé, qalivâš, qalivâj,
(Qäyen, Gonâbâd) kaliždak, (Xorâsâni) kelidjak, (Dari Yazd) kelociri, (Bardesir) kerâcik, related to kalâq + dimunitive suffix -iž, vaeiants -iz, -ak.

Chief in size, extent, or importance; leading; → principal.

Etymology (EN): From M.E. meyn, mayn “strength, power,”
from O.E. mægen “power, strength, force,” from P.Gmc. *maginam- “power,” from *mag- “to be able, have power.”

Etymology (PE): Farist, literally “foremost” (cf. Mid.Pers. frahist “main, principal, first, much”), from far-, Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā “forth,” pouruua- “first”; cf.
Skt. pūrva- “first,” pra- “before, formerly;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore, E. fore + -est superlative suffix, Mid.Pers. -ist, -išt-; Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

Chief in size, extent, or importance; leading; → principal.

Etymology (EN): From M.E. meyn, mayn “strength, power,”
from O.E. mægen “power, strength, force,” from P.Gmc. *maginam- “power,” from *mag- “to be able, have power.”

Etymology (PE): Farist, literally “foremost” (cf. Mid.Pers. frahist “main, principal, first, much”), from far-, Mid.Pers. fra-; O.Pers. fra- “forward, forth;” Av. frā “forth,” pouruua- “first”; cf.
Skt. pūrva- “first,” pra- “before, formerly;” Gk. pro; L. pro; O.E. fyrst “foremost,” superlative of fore, E. fore + -est superlative suffix, Mid.Pers. -ist, -išt-; Av. -išta-, cf. Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost.

Same as → main lobe.

See also: → main; → beam.

Same as → main lobe.

See also: → main; → beam.

The area between → Mars and → Jupiter where most of the → asteroids in our → solar system are found.

See also: → main; → belt.

The area between → Mars and → Jupiter where most of the → asteroids in our → solar system are found.

See also: → main; → belt.

In the n x n → matrix , the entities a₁₁, a₂₂, …, a_nn.

See also: → main; → diagonal.

In the n x n → matrix , the entities a₁₁, a₂₂, …, a_nn.

See also: → main; → diagonal.

The lobe in the reception pattern of a radio telescope
that includes the region of the maximum received power. Also called major lobe and main beam.

See also: → main; → lobe.

The lobe in the reception pattern of a radio telescope
that includes the region of the maximum received power. Also called major lobe and main beam.

See also: → main; → lobe.

A thin strand of material encircling Jupiter;
the main component in → Jupiter’s ring system of three parts. The diffuse innermost boundary begins at approximately 123,000 km. The main ring’s outer radius is found to be at 128,940 km,

See also: → main; → ring.

A thin strand of material encircling Jupiter;
the main component in → Jupiter’s ring system of three parts. The diffuse innermost boundary begins at approximately 123,000 km. The main ring’s outer radius is found to be at 128,940 km,

See also: → main; → ring.

An evolutionary stage in the life of a star when it generates its energy by the conversion of hydrogen to helium via → nuclear fusion in its core. Stars spend 90% of their life on the main sequence. On the → Hertzsprung-Russell diagram it appears as a track running from top left (high temperature, high luminosity, high mass) to lower right (low temperature, low luminosity, low mass). See also → zero age main sequence (ZAMS), → terminal age main sequence (TAMS).

See also: → main; → sequence.

An evolutionary stage in the life of a star when it generates its energy by the conversion of hydrogen to helium via → nuclear fusion in its core. Stars spend 90% of their life on the main sequence. On the → Hertzsprung-Russell diagram it appears as a track running from top left (high temperature, high luminosity, high mass) to lower right (low temperature, low luminosity, low mass). See also → zero age main sequence (ZAMS), → terminal age main sequence (TAMS).

See also: → main; → sequence.

The method of determining the distance to a star cluster by overlaying its main sequence on the theoretical zero-age main sequence and noting the difference between the cluster’s apparent magnitude and the zero-age main sequence’s absolute magnitude.

See also: → main sequence; → fitting.

The method of determining the distance to a star cluster by overlaying its main sequence on the theoretical zero-age main sequence and noting the difference between the cluster’s apparent magnitude and the zero-age main sequence’s absolute magnitude.

See also: → main sequence; → fitting.

The point on the → Hertzsprung-Russell diagram of a star cluster at which stars begin to leave the → main sequence and move toward the → red giant branch. The main-sequence turnoff is a measure of age. In general, the older a star cluster, the
fainter the main-sequence turnoff. Same as → turnoff point.

See also: → main sequence; → turnoff.

The point on the → Hertzsprung-Russell diagram of a star cluster at which stars begin to leave the → main sequence and move toward the → red giant branch. The main-sequence turnoff is a measure of age. In general, the older a star cluster, the
fainter the main-sequence turnoff. Same as → turnoff point.

See also: → main sequence; → turnoff.

Greater in size, extent, or importance.

Etymology (EN): M.E. majour, from O.Fr., from
L. major, irregular comparative of magnus “large, great,” cognate with Pers. meh “large, great,” as below.

Etymology (PE): Mehin comparative and superlative of
meh “great, large”
(Mid.Pers. meh, mas; Av. maz-, masan-, mazant- “great, important,” mazan- “greatness, majesty,” mazišta- “greatest;” cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- “great”) + -in superlative suffix.

Greater in size, extent, or importance.

Etymology (EN): M.E. majour, from O.Fr., from
L. major, irregular comparative of magnus “large, great,” cognate with Pers. meh “large, great,” as below.

Etymology (PE): Mehin comparative and superlative of
meh “great, large”
(Mid.Pers. meh, mas; Av. maz-, masan-, mazant- “great, important,” mazan- “greatness, majesty,” mazišta- “greatest;” cf. Skt. mah-, mahant-; Gk. megas; PIE *meg- “great”) + -in superlative suffix.

The greatest diameter of an ellipse; it passes through the two foci.

See also: → major; → axis.

The greatest diameter of an ellipse; it passes through the two foci.

See also: → major; → axis.

The → merging of two spiral galaxies with roughly equal masses colliding at appropriate angles. The dynamical friction is so efficient that the galaxies merge after only a few perigalactic passages.

See also: → major; → merger.

The → merging of two spiral galaxies with roughly equal masses colliding at appropriate angles. The dynamical friction is so efficient that the galaxies merge after only a few perigalactic passages.

See also: → major; → merger.

A name used to describe any planet that is considerably larger and more massive than the Earth, and contains large quantities of hydrogen and helium. Jupiter and Neptune are examples of major planets.

See also: → major; → planète.

A name used to describe any planet that is considerably larger and more massive than the Earth, and contains large quantities of hydrogen and helium. Jupiter and Neptune are examples of major planets.

See also: → major; → planète.

Logic: In a → categorical syllogism, the premise containing the → major term.

See also: → major; → premisse.

Logic: In a → categorical syllogism, the premise containing the → major term.

See also: → major; → premisse.

Logic: In a → syllogism, the → predicate of the → conclusion which occurs in the → major premise.

See also: → major; → term.

Logic: In a → syllogism, the → predicate of the → conclusion which occurs in the → major premise.

See also: → major; → term.

A function, or an element of a set, that dominates others or is greater than all others. In other words, for a function f defined on the interval I, the point M such that for each x on I, f(x)≤ M. See also → minorant.

Etymology (EN): From Fr. majorant, from majorer “to increase, raise,” from L. → major.

Etymology (PE): Mehân, from mehidan, from meh “great, large,” → major.

A function, or an element of a set, that dominates others or is greater than all others. In other words, for a function f defined on the interval I, the point M such that for each x on I, f(x)≤ M. See also → minorant.

Etymology (EN): From Fr. majorant, from majorer “to increase, raise,” from L. → major.

Etymology (PE): Mehân, from mehidan, from meh “great, large,” → major.

The greater number, part, or quantity of a whole.

See also: → major; → -ity.

The greater number, part, or quantity of a whole.

See also: → major; → -ity.

The third largest known → dwarf planet after → Eris and → Pluto. Numbered 136472, and initially called 2005 FY_g, it
belongs to the → Kuiper belt in the solar system. Discovered in 2005, Makemake is roughly three-quarters of Pluto in size and orbits the Sun in about 310 years.

See also: Named after Makemake “the creator of humanity and god of fertility” in the mythology of the Rapanui, the native people of Easter Island.

The third largest known → dwarf planet after → Eris and → Pluto. Numbered 136472, and initially called 2005 FY_g, it
belongs to the → Kuiper belt in the solar system. Discovered in 2005, Makemake is roughly three-quarters of Pluto in size and orbits the Sun in about 310 years.

See also: Named after Makemake “the creator of humanity and god of fertility” in the mythology of the Rapanui, the native people of Easter Island.

Something put in a scale to complete a required weight.

Etymology (EN): → make; → weight.

Etymology (PE): Pârsang, → counterweight.

Something put in a scale to complete a required weight.

Etymology (EN): → make; → weight.

Etymology (PE): Pârsang, → counterweight.

A → reflecting telescope incorporating a deeply curved → meniscus, → lens, which corrects the → optical aberrations of the spherical → primary mirror to give high-quality → images over a wide → field of view.

See also: Named for the Russian optical specialist Dmitri Maksutov (1896-1964), who developed the design; → telescope.

A → reflecting telescope incorporating a deeply curved → meniscus, → lens, which corrects the → optical aberrations of the spherical → primary mirror to give high-quality → images over a wide → field of view.

See also: Named for the Russian optical specialist Dmitri Maksutov (1896-1964), who developed the design; → telescope.

1. Belonging to the sex that typically has the capacity to produce gametes, especially spermatozoa which fertilize the eggs of a female.
   

   2. A person, plant, or animal capable of fertilizing.

Etymology (EN): M.E. male, from O.Fr. malle, masle, from L. masculus “masculine, a male,” → maculine.

Etymology (PE): Nar “male,” from Mid.Pers. nar, “male; manly;” Av. nar- “male, man,” nairya- “male, manly;” cf. Skt nara- “male, man.”

1. Belonging to the sex that typically has the capacity to produce gametes, especially spermatozoa which fertilize the eggs of a female.
   

   2. A person, plant, or animal capable of fertilizing.

Etymology (EN): M.E. male, from O.Fr. malle, masle, from L. masculus “masculine, a male,” → maculine.

Etymology (PE): Nar “male,” from Mid.Pers. nar, “male; manly;” Av. nar- “male, man,” nairya- “male, manly;” cf. Skt nara- “male, man.”

A selection effect in observational astronomy. If a sample of objects (galaxies, quasars, stars, etc.) is flux-limited, then the observer will see an increase in average luminosity with distance, because the less luminous sources at large distances will not be detected.

See also: Named after the Swedish astronomer Gunnar Malmquist (1893-1982); → bias.

A selection effect in observational astronomy. If a sample of objects (galaxies, quasars, stars, etc.) is flux-limited, then the observer will see an increase in average luminosity with distance, because the less luminous sources at large distances will not be detected.

See also: Named after the Swedish astronomer Gunnar Malmquist (1893-1982); → bias.

A correction introduced into star counts distributed by apparent magnitude.

See also: → Malmquist bias; → correction.

A correction introduced into star counts distributed by apparent magnitude.

See also: → Malmquist bias; → correction.

If the light wave entering an → analyzer is → linearly polarized, the intensity of the wave emerging from the analyzer is I = k I₀ cos²φ,

where k is the coefficient of transmission of the analyzer, I₀ is the intensity of the incident light, and φ is the angle between the planes of → polarization of the incident light and the light emerging from the analyzer.

See also: Named after Etienne Louis Malus (1775-1812), French physicist who also discovered polarization by reflection at a glass surface (1808); → law.

If the light wave entering an → analyzer is → linearly polarized, the intensity of the wave emerging from the analyzer is I = k I₀ cos²φ,

where k is the coefficient of transmission of the analyzer, I₀ is the intensity of the incident light, and φ is the angle between the planes of → polarization of the incident light and the light emerging from the analyzer.

See also: Named after Etienne Louis Malus (1775-1812), French physicist who also discovered polarization by reflection at a glass surface (1808); → law.

A method for deriving the Earth’s size based on measuring a length of meridian between two points corresponding to the difference between the respective latitudes. The Abbasid caliph al-Ma’mun (ruling from 813 to 833 A.D.), appointed two teams of surveyors to this task. They departed from a place in the desert of Sinjad (nineteen farsangs from Mosul and forty-three from Samarra), heading north and south, respectively. They proceeded until they found that the height of the Sun at noon had increased (or decreased) by one degree compared to that for the starting point. Knowing the variation of the Sun’s → declination due to its apparent → annual motion, they could relate the length of the arc of meridian to the difference between the latitudes of the two places. They repeated the measurement a second time, and so found that the length of one degree of latitude is somewhat between 56 and 57 Arabic miles (Biruni, Tahdid). 360 times this number yielded the Earth’s circumference, and from it the radius was deduced.

See also: → Eratosthenes’ method, → Biruni’s method.

See also: The seventh Abbasid caliph Abu Ja’far Abdullâh al-Ma’mûn, son of Hârûn al-Rashîd (786-833 A.D.); → method.

A method for deriving the Earth’s size based on measuring a length of meridian between two points corresponding to the difference between the respective latitudes. The Abbasid caliph al-Ma’mun (ruling from 813 to 833 A.D.), appointed two teams of surveyors to this task. They departed from a place in the desert of Sinjad (nineteen farsangs from Mosul and forty-three from Samarra), heading north and south, respectively. They proceeded until they found that the height of the Sun at noon had increased (or decreased) by one degree compared to that for the starting point. Knowing the variation of the Sun’s → declination due to its apparent → annual motion, they could relate the length of the arc of meridian to the difference between the latitudes of the two places. They repeated the measurement a second time, and so found that the length of one degree of latitude is somewhat between 56 and 57 Arabic miles (Biruni, Tahdid). 360 times this number yielded the Earth’s circumference, and from it the radius was deduced.

See also: → Eratosthenes’ method, → Biruni’s method.

See also: The seventh Abbasid caliph Abu Ja’far Abdullâh al-Ma’mûn, son of Hârûn al-Rashîd (786-833 A.D.); → method.

1. An adult male person.
   

2. A member of the species Homo sapiens. See also → human, → anthropo-.

Etymology (EN): M.E., from O.E. man, mann “human being, person” (O.S., O.H.G. man, Ger. Mann, O.N. maðr, Goth. manna “man”), from PIE base *man-;
cf. Skt. mánu-, más- “man, person, husband;”
Av. manu- in proper noun Manus-ciθra- (Pers. Manucehr); O.C.S. moži, Russ. muž “man, male.”

Etymology (PE): (Mid.Pers./Mod.Pers.) mard “man,” mardom “mankind, people,” cognate with mordan “to die,” → death;
Sogd. martu, marti “man, human;” O.Pers. martiya-; Av. marəta- “mortal, man,” maša- “mortal;” cf. Skt. márta- “mortal, man;” Gk. emorten “died;” L. mortalis “subject to death;” PIE base *merto-, *morto-. Ensân, loan from Ar.

1. An adult male person.
   

2. A member of the species Homo sapiens. See also → human, → anthropo-.

Etymology (EN): M.E., from O.E. man, mann “human being, person” (O.S., O.H.G. man, Ger. Mann, O.N. maðr, Goth. manna “man”), from PIE base *man-;
cf. Skt. mánu-, más- “man, person, husband;”
Av. manu- in proper noun Manus-ciθra- (Pers. Manucehr); O.C.S. moži, Russ. muž “man, male.”