Presidential Lecture 1992 - James A. Van Allen Figure 5. A schematic diagram of the motion of an electrically charged par ticle in the external magnetic field of the Earth. The particle gyrates around a line of magnetic force, os cillates from one hemisphere to the other, and gradually drifts in longi tude around the Earth within a toroidal-shaped region.
Protons drift westward and electrons, eastward.
The pictured particle is one of a huge number of such particles that consti tute a radiation belt.