| either of two regions of high-energy-charged particles surrounding the earth, the inner region centered at an altitude of 2000 mi. (3200 km) and the outer region at an altitude between 9000 and 12,000 mi. (14,500 and 19,000 km). |
Van Al·len belt  (vān āl'ən)  n. Either of two zones of high-intensity particulate radiation trapped in Earth's magnetic field and surrounding the planet, beginning at an altitude of about 800 kilometers (500 miles) and extending tens of thousands of kilometers into space. [After James Alfred Van Allen (1914-2006), American physicist.] |
Either of two layers of electrically charged (see electrical charge) particles held in orbits above the atmosphere by the magnetic field of the Earth. The belt is named after its discoverer, the twentieth-century American physicist James Van Allen.
Van Allen belt (vān āl'ən) Pronunciation Key
(click for larger image in new window) Either of the two zones surrounding the Earth in which a thin distribution of atomic particles with very high energies are trapped by Earth's magnetic field. The inner belt lies between about 500 and 6,440 km (310 to 4,000 mi) above Earth's equator and consists mostly of a mix of protons and electrons. The upper belt lies between about 15,000 and 30,000 km (9,300 to 18,600 mi) and consists mostly of protons. Both belts are thickest at the equator and have irregular densities of particles. The outer radiation belt is much larger and the number of particles varies, increasing in the aftermath of solar flares. The polar auroras are caused when some of the charged particles from the outer Van Allen belt hit the upper atmosphere. The Van Allen belt is named after its discoverer, American astrophysicist James Van Allen (born 1914). |
