Geosynchronous Satellite - Definition

Definition

According to Kepler's Third Law, the orbital period of a satellite in a circular orbit increases with increasing altitude. Space stations and Shuttles in Low Earth orbit (LEO), typically two to four hundred miles above the Earth's surface, make between fifteen and sixteen revolutions per day. The Moon, at an altitude of about 238,900 miles (384,400 km), takes about 27 days 7 hours to make a complete revolution. Between those extremes lies the "magic" altitude of 22,236 miles (35,786 km) at which a satellite's orbital period matches the period at which the Earth rotates: once every sidereal day (23 hours 56 minutes 4 seconds). In that case, the satellite is said to be geosynchronous.

If a geosynchronous satellite's orbit is not exactly aligned with the Earth's equator, the orbit is known as an inclined orbit. It will appear (when viewed by someone on the ground) to oscillate daily around a fixed point. As the angle between the orbit and the equator decreases, the magnitude of this oscillation becomes smaller; when the orbit lies entirely over the equator, assuming a circular orbit, the satellite remains stationary relative to the Earth's surface – it is said to be geostationary.