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Geostationary satellites

These satellites are the ones used for relaying TV and radio communications round the world. The signal is transmitted from the ground, received by the satellite which then transmits it to the receiver on the ground. They are now a vital part of our lives. Almost all international communications are relayed by communication satellites.

This animation shows two satellites, one geostatiuonary (orange) and one non-geostationary (light blue).

Geostationary satellites 'hang' in the sky above one point on the Earth's surface - they have a period of revolution equal to the rotation period of the Earth. In other words they take one day to make one revolution. This means that ground based aerials do not have to be moved to pick up the transmissions from them.

For the Earth all synchronous satellites are in an orbit 42000 km from the Earth's centre (about 6 Earth radii) - a potential problem for cosmic junk!

Summary of the properties of a geostationary satellite (for the Earth):
(a) they have an orbit which lies in the same plane as the equator of the Earth
(b) the period of the satellite is one Earth day
(c) they have the same angular velocity as the Earth
(d) the move around their orbit in the same direction as the rotation of the Earth
(e) they remain above a fixed point on the Earth's surface.
© Keith Gibbs/John Bourne 2016