Geosynchronous orbit

A geosynchronous orbit is an orbit around a planet with an orbital period matching the planet's sidereal rotation period. The term geosynchronous can be used to describe any orbital pattern with a period equal to that of its orbiting body, and in the same direction as the parent's rotation, but is specifically used for orbits with no inclination and a semimajor axis of equal length to the minor axis (i.e. circular). Satellites in geosynchronous orbits appear to maintain their longitude, while their latitude oscillates in a 24-hour period. The geosynchronous orbit over the equator is called the geostationary orbit. Satellites in the geostationary orbit appear stationary relative to the planet's surface.

Orbital Defense Platforms in particular make use of geosynchronous orbits to protect certain ground regions from attack; Cairo Station, for example, orbited over the city of Cairo, taking its name. The Athens Station orbited above the Greek city of Athens. Other satellites, predominately telecommunication satellites, orbit in traditional geostationary orbits, holding over the same point during every rotation of the Earth. The terminus stations of Space Elevators are also anchored to a geosynchronous, near-geostationary orbit.