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This is an artist's conception of the Earth and its radiation belts.
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The Discovery of the Radiation Belts

The belts of trapped radiation above the Earth's atmosphere, but within the magnetosphere, were first detected by James Van Allen in 1958. Therefore these belts are also known as Van Allen Belts.

When Sputnik I, the first spacecraft, was launched in 1957 by the Soviet Union, the Americans were anxious to respond.

Dr. James Van Allen had already been exploring the upper atmosphere of the Earth with balloons that could measure radiation levels in the atmosphere. Van Allen and his team placed a Geiger counter and an altimeter on Explorer I, the first American spacecraft, to take radiation readings at different heights.

During the flight, radiation levels seemed to increase and then suddenly drop to zero and then again to increase, then suddenly drop to zero. What the team soon realized was that regions appearing as zero were really off the scale! These high-radiation regions were mapped and are now known as the Van Allen radiation belts.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF