Though we tend instantly to think of "satellites" as the shiny, pod-like crafts whizzing around Earth at high altitude, a satellite is technically any object that revolves around a planet in a path that is circular or elliptical. Therefore there are three major types of satellites. The first group is natural satellites -- our moon would be an example, since it naturally orbits the Earth. Moons of other planets, would, of course, also apply. The other two types of satellites are both artificial satellites. An artificial satellite can either be custom-built or mass-produced. GPS and Iridium satellites have been made in mass, while the rest of the artificial satellites are usually custom-built for specific purposes, such as for satellite-distributed television service.
By definition, satellites revolve around something, and artificial satellite orbits of the Earth come in several flavors: polar orbits, sun synchronous orbits and geosynchronous (also called geostationary) orbits. Polar orbit satellites fly around the Earth in about 90 minutes and, because of their "viewpoint," circling from pole to pole, are able to see the almost the whole surface of the spinning world below them. Sun synchronous satellites help craft that need constant sunlight; and geosynchronous satellites fly around the Earth at the same speed as our planet spins, positioned near the equator, with almost-full views of the hemispheres [source: Rutgers University].
While satellites have uses ranging from pure science to military to consumer applications, communications satellites impact most peoples' everyday lives. They transfer telephone and data conversations all over the world. Each satellite can contain thousands of transponders, which receive radio signals from Earth and relay them back. A signal will come into the transponder at one frequency, and the satellite will transmit it back to Earth at a different frequency. Two examples of communications satellites are Telstar and Intelsat.
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