FAR MAGNETIC FIELDS
The magnetosphere is that part of the magnetic field surrounding the earth that exerts a force strong enough to control the motions of charged subatomic particles entering the field. Exerting a strong force even 50,000 kilometers away from the earth's surface, this magnetic field protects us from bombardment by many of the charged subatomic particles traveling through space at speeds that are a significant fraction of the speed of light.
From satellites monitoring the magnetic field we have learned much about the magnetosphere's strength, direction, and composition. It has several concentric zones; the pri ncipal ones are zones of high subatomic-particle densities known as the Van Allen radiation belts (named after American physicist James Van Allen, (1914- ) who discovered their existence in 1958 from Explorer satellite data). The Van Allen belts encircle the planet in two doughnutshaped regions about 3,000 and 17,000 kilometers from the earth's surface.
Charged particles, mainly protons and electrons, populate the magnetosphere's radiation belts. Most of these subatomic particles are ejected from the sun as a reasonably steady flow of matter in the plane of the ecliptic known as the solar wind. When the solarwind particles encounter the earth, they are either diverted away from it or trapped by its magnetic field.
The collision of solar-wind particles with the earth's magnetosphere creates a shock wave that distorts and compresses the magnetic field on the sunlit side and stretches it into a long tail on the night side. (A shock wave is a large-amplitude compression, such as the sonic boom made by a jet plane.)
