Van Allen radiation belts

Van Allen radiation belts

(van al -ĕn) Two regions within the Earth's magnetosphere in which charged particles become trapped and oscillate backward and forward between the magnetic poles as they spiral around magnetic field lines. The lower belt, which on average lies 5000 km above the equator, contains protons and electrons either captured from the solar wind or derived from collisions between upper atmosphere atoms and high-energy cosmic rays. The upper belt lies between about 25 000 and 36 000 km or more above the equator but curving downward toward the magnetic poles; it contains fewer and less-energetic particles than the lower belt, mainly electrons from the solar wind. The belts were discovered by James Van Allen in the course of his analysis of observations by early Explorer satellites in 1958.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006