Figure 5. A schematic diagram of the motion of an electrically charged par­ticle in the external magnetic field of the Earth. The particle gyrates around a line of magnetic force, os­cillates from one hemisphere to the other, and gradually drifts in longi­tude 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 consti­tute a radiation belt.