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a region in which magnetic forces can be observed. See "electromagnetic field," a more general field also including electric forces.
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lines in space, used for visually representing magnetic fields. At any point in space, the local field line points in the direction of the magnetic force which an isolated magnetic pole at that point would experience. In a plasma, magnetic field lines also guide the motion of ions and electrons, and direct the flow of some electric currents.
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(1)Magnetic poles of a magnet are points near its ends, at which the magnetic force seems concentrated.
(2) The magnetic poles of the Earth are the point towards which a horizontal compass needle tends to point. Several alternative definitions exist, giving slightly different locations, e.g. the "dip pole" is where the magnetic force is purely vertical.
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Electric charges come in two varieties, denoted (+) and (-). Similarly , the poles of a magnet have different magnetic polarities, "north-seeking" (N) and "south-seeking" (S). If the magnet is freely suspended (e.g. a compass needle), the (N) end turns to face north, the (S) turns to face south. Like electric charges, poles of the same kind repel, of opposite kinds attract.
The names are usually abbreviated to "north" and "south" poles, which occasionally causes confusion. If the magnetic properties of the Earth came from it being a giant magnet (rather than from electric currents in its interior) then the magnetic pole close to its northern geographic pole would in fact be an "S" pole or "south seeking" pole--since it attracts the north-seeking pole of the compass needle!
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A large-scale disturbance of the magnetosphere, often initiated by the arrival of an plasma cloud originating at the Sun.
A magnetic storm is marked by the injection of an appreciable number of ions from the tail regions of the magnetosphere into ]the near-Earth magnetosphere, a process accompanied by increased auroral displays. The injected particles cause a world-wide drop in the equatorial magnetic field, taking perhaps 12 hours to reach its greatest intensity, followed by a more gradual recovery.
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The outermost environment of Earth, dominated by the Earth's magnetic field. The magnetosphere is the site of the radiation belt and many intricate phenomena. See solar wind.
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The mass of a body can be loosely defined as the amount of matter it contains. That is expressed in two ways:
inertial mass, the resistance of the matter to acceleration or deceleration, as given by the factor m in Newton's 2nd law F = ma
gravitational mass, the force exerted on the matter by gravity ("weight"), given near the surface of Earth by F = mg.
According to all experiments, the two are equal, causing all bodies subject to gravity only (near the surface of the Earth) to have the same acceleration a = g.
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An angle used in calculating orbital motion obeying Kepler's laws, increasing by 360 degrees each orbit. The polar angle of an orbiting object around the center of attraction--the "true anomaly"--also increases by 360 degrees each orbit. However, while the true anomaly changes unevenly--faster during closest approach--the mean anomaly increases steadily, in proportion to time. The mean anomaly is one of 6 orbital elements defining Keplerian motion.
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Named for the Athenian astronomer Meton, it is based on the moon, counting each cycle of the phases of the Moon as one month. Days are kept approximately in step with the seasons by including 7 leap years of 13 months in each cycle of 19 years. Used by the Chinese and the Jews.
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Electromagnetic waves longer than infra-red but shorter than radio, with typical wavelength 0.1-10 centimeters.
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Theory by which ice ages were caused by slow changes of the motion of the Earth in space, including the coupling between the 26 000 year cycle of the precession of the equinoxes and the annual variation of the Earth-Sun distance.
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(plural: momenta). The momentum of a moving object is the product (result of multiplication) of its mass and velocity; like velocity, momentum is a vector. The law of conservation of momentum states that when two or more objects interact--a cannon fires a shell, a rocket shoots out a fast jet of hot gas, a bowling ball scatters a group of pins--the total vector sum of their momenta is unchanged. That, too, is an equivalent formulation of Newton's laws.
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Based on a year of 12 months, each corresponding to one cycle of the Moon, but without the Metonic correction. Its months migrate through the seasons.
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