What is Geostationary Orbit?

The term geostationary orbit combines two words, ‘geo’ from Greek, which means ‘the earth’ and ‘stacionarie’, from Middle English, which means ‘stationary’. Thus, the word signifies something that is stationary with respect to the earth. And this is exactly how the definition goes: it is an orbit around a planet or a moon in which the time needed to move once around the parent planet or the moon (orbital period) matches the rotation rate of the parent planet or the moon (sidereal rotation).

A geostationary orbit is a special case of ‘geosynchronous orbit’ and the terms aren’t always interchangeable. A geosynchronous orbit is at an angle with respect to the plane of the rotation of a planet but a ‘geostationary orbit’ is normally directly above the equator. So, when the latitude of a ‘geosynchronous orbit’ is zero it is a ‘geostationary orbit’.

If a satellite is in a geostationary orbit, its ground track which is its trail on the earth will be a point on the equator. In other words, it would always hover over the same point on the equator and appear to us from the earth as being motionless in the sky.

A geostationary orbit has to have a required distance from the parent body else the satellite put into the orbit would either fall back to  the parent body or simply shoot up into outer space, beyond recovery.

For the earth, the distance is measured at around 36000 km directly above the equator and an orbital velocity of approximately 3 km/s is required for a satellite to remain in the geostationary orbit.

This property of being constantly over a particular point is of special interest because communication satellites are put into this orbit.

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