A geo-stationary satellite is an earth-orbiting satellite place at an altitude of approximately 36,000 km directly over the equator that revolves in the same direction in which the earth rotates (west to east). At this altitude, one orbit takes 24 hours, which is the same length of time that the earth requires to rotate once on its on axis. The term geo-stationary comes from the fact that such a satellite appears nearly stationary in the sky as seen by a ground-based observer.