Television pictures, radio and telephone communications are bounced off satellites to cover the greatest possible area of the world. Satellites orbiting the Earth must travel at high speed to escape being brought down by the Earth’s gravity. As the Earth itself is spinning rapidly, there is a point above the Earth’s surface where the orbiting speed of the satellite can be matched with the rotational speed of the Earth. At this point —35,900 kilometres above the Earth — the satellite appears to stand still and is said to be in a geostationary orbit.
Geostationary satellites can be positioned right over the areas where they are needed. They can also be used as spy satellites, because they remain constantly over a region of interest.
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