Van Allen radiation belts
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Van Allen radiation belts,belts of radiation outside the earth's atmosphere, extending from c.400 to c.40,000 mi (c.650–c.65,000 km) above the earth. The existence of two belts, sometimes considered as a single belt of varying intensity, was confirmed from information secured by launching the first U.S. earth satellite, Explorer I, sent up during the International Geophysical YearInternational Geophysical Year
(IGY), 18-month period from July, 1957, through Dec., 1958, during a period of maximum sunspot activity, designated for cooperative study of the solar-terrestrial environment by the scientists of 67 nations.
..... Click the link for more information. of 1957–58. The belts were named for James A. Van AllenVan Allen, James Alfred,
1914–2006, American physicist and space scientist, Mt. Pleasant, Iowa. A graduate (Ph.D 1939) of and professor of physics (1951–85) at what is now the Univ.
..... Click the link for more information. , the American astrophysicist who first predicted the belts and then was first to interpret the findings of the Explorer satellite. In 2012 NASA space probes studying the belt tracked the formation of a third belt, between the two belts previously known. This third belt and the outer belt disappeared several weeks after the third belt appeared; the outer belt subsequently re-formed.
The region of the radiation belts has been given the name of magnetosphere to distinguish it from the atmosphereatmosphere
[Gr.,=sphere of air], the mixture of gases surrounding a celestial body with sufficient gravity to maintain it. Although some details about the atmospheres of other planets and satellites are known, only the earth's atmosphere has been well studied, the science of
..... Click the link for more information. . The high-energy particles of which the belts are composed circulate along the earth's magnetic lines of force extending from the area above the equator to near (but not above) the North and South Poles. The inner belt is mainly protons with some electrons; the outer one mainly electrons. The particles of the inner belt are believed to be produced by the collisions of cosmic rayscosmic rays,
charged particles moving at nearly the speed of light reaching the earth from outer space. Primary cosmic rays consist mostly of protons (nuclei of hydrogen atoms), some alpha particles (helium nuclei), and lesser amounts of nuclei of carbon, nitrogen, oxygen, and
..... Click the link for more information. with atoms in the upper atmosphere. Those of the outer belt are believed to originate both from the atmosphere and from the solar windsolar wind,
stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds.
..... Click the link for more information. ; particles from the solar wind become trapped by the earth's magnetic field and are responsible for the aurora borealisaurora borealis
and aurora australis
, luminous display of various forms and colors seen in the night sky. The aurora borealis of the Northern Hemisphere is often called the northern lights, and the aurora australis of the Southern Hemisphere is known as the southern
..... Click the link for more information. seen at polar regions. A part of a belt dips into the upper region of the atmosphere over the South Atlantic to form the Southern Atlantic Anomaly. This can present a dangerous hazard to satellites orbiting the earth.