Geosynchronous Orbit

A Geosynchronous Orbit (sometimes abbreviated GSO) is an orbit around the any planetoid with an orbital period that matches the that planetoid's sidereal rotation period. The synchronization of rotation and orbital period means that for an observer on the surface of the planetoid, the satellite appears to constantly hover over the same meridian (north-south line) on the surface, moving in a slow oscillation alternately north and south with a period of one standard day, so it returns to exactly the same place in the sky at exactly the same time each day.

However, the term is often popularly used to refer to the special case of a geosynchronous orbit called a geostationary orbit. This is a geosynchronous orbit that is circular and at zero inclination, that is, directly above the equator. A satellite in a geostationary orbit appears stationary, always at the same point in the sky, to ground observers. Orbital stations and satellites are often given geostationary orbits, or close to geostationary, so that the satellite antennas that communicate with them don't have to move, but can be pointed permanently at the fixed location in the sky where the satellite appears.