- either of two regions of high-energy-charged particles surrounding the earth, the inner region centered at an altitude of 2,000 miles (3,200 km) and the outer region at an altitude between 9000 and 12,000 miles (14,500 and 19,000 km).
- either of two regions of charged particles above the earth, the inner one extending from 2400 to 5600 kilometres above the earth and the outer one from 13 000 to 19 000 kilometres. The charged particles result from cosmic rays and are trapped by the earth's magnetic field
