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A geostationary orbit (or Geostationary Earth Orbit - GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. A person watching from Earth sees a object in a geostationary orbit as motionless, at a fixed position in the sky. Communications satellites and weather satellites often have geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them. The ground atennas can be pointed permanently at a fixed position in the sky. With fixed 0° latitude and circularity of geostationary orbits, satellites in GEO differ in location by longitude only.
The notion of a geosynchronous satellite for communication purposes was first published in 1928 (but not widely so) by Herman Potočnik. The idea of a geostationary orbit was first disseminated on a wide scale in a 1945 paper entitled "Extra-Terrestrial Relays — Can Rocket Stations Give Worldwide Radio Coverage?" by British science fiction writer Arthur C. Clarke, published in Wireless World magazine. The orbit, which Clarke first described as useful for broadcast and relay communications satellites, is sometimes called the Clarke Orbit. Similarly, the Clarke Belt is the part of space about 35,786 km (22,000 mi) above sea level, in the plane of the equator, where near-geostationary orbits may be implemented. The Clarke Orbit is about 265,000 km (165,000 mi) long.
The satellite orbits in the direction of the Earth's rotation, at an altitude of 35,786 km (22,236 mi) above ground, producing an orbital period equal to the Earth's period of rotation, known as the sidereal day.
- Noordung, Hermann; et al. (1995) . The Problem With Space Travel. Translation from original German. DIANE Publishing. pp. 72. ISBN 978-0788118494.
- "Extra-Terrestrial Relays — Can Rocket Stations Give Worldwide Radio Coverage?". Arthur C. Clark. October 1945. http://www.clarkefoundation.org/docs/ClarkeWirelessWorldArticle.pdf. Retrieved 2009-03-04.
- "Basics of Space Flight Section 1 Part 5, Geostationary Orbits". NASA. http://www2.jpl.nasa.gov/basics/bsf5-1.php. Retrieved 2009-06-21.