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Geostationary or Geosynchronous Orbits

From Earth a geostationary or geosynchronous satellite appears to stay still, always above the same point on the Earth's surface.

This is because, orbiting very high above the Earth, at an altitude of about 36,000 kilometres, geostationary satellites orbit the Earth once every 24 hours. It is sychronised with the rotation of the Earth.

This orbit allows the satellite to monitor the same region of the Earth all of the time.

The area to which it can transmit is called a satellite's footprint. This footprint can be very large indeed - for example, many Canadian communications satellites have a footprint which covers most of Canada.

Geostationary satellites usually measure in "real time", meaning they transmit photographs to the receiving system on the ground as soon as the camera takes the picture. A series of photographs from these satellites can be displayed in sequence to produce a movie showing cloud movement.

This allows weather forecasters to watch the progress of large weather systems such as fronts, storms, and hurricanes. Forecasters can also find out the wind direction and speed by monitoring cloud movement. geostationary satellites are therefore used as weather satellites.

They are also used as communications satellites.