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We now offer the Cool It! card game in our Science Store. Cool It! is the new card game from UCS that teaches kids about the choices we have when it comes to climate change.

When a satellite is held in orbit, what is it orbiting relative to? What's so special about the orbit of geosynchronous satellites?

Well, you're on to something, Elliott. The Space Satellite Handbook defines a satellite as a small body orbiting a larger body. So when a satellite is held in orbit, it is orbiting relative to a larger body. An example is the Surveyor probe which just entered into orbit around Mars. The Surveyor is a satellite in this system because it orbits Mars (the larger body).

Geosynchronous satellites are those man-made satellites which always orbit the Earth at an altitude of 35,785 kilometers (22,236 miles). But that's not all that is special about these satellites. These satellites revolve around the Earth at the same speed at which the Earth rotates, or geosynchronous satellites complete one orbit in exactly one Earth day. Because the orbital velocity matches the spin rate of the Earth, a satellite in geosynchronous orbit appears to hover motionless over a single location on Earth. Because these satellites always look at the same region of the Earth, they are often used to study environmental conditions for that specific region.

In 1945, Arthur C. Clarke wrote of such satellites that would hang stationary over one spot on the Earth's surface. So the region of space where geosynchronous satellites fly is fondly termed the Clarke Belt.

Submitted by Elliott (England)
(September 30, 1997)



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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA