What is a satellite?

A satellite is an object that orbits a planet. The Moon is Earth satellite, and all the planets except Mercury and Venus have them. Natural satellites, however, are usually referred to as moons, and man-made satellites, often called artificial satellites, are what is usually meant by the word 'satellite'.

There are about 1,000 of them working in space right now. Each one is a scientific package designed to carry out a particular job. They orbit between about 300 and 1000 km above Earth's surface and are launched into orbit by a rocket or occasionally by a space shuttle.

Space satellites have revolutionized communications, making possible everyday developments such as mobile phones and television. Communications satellites receive signals beamed at them from the Earth, and send them on to other places. They transmit television and telephone signals around the world, even to remote areas. They are also used for defence communications, including checking on the movement of military forces. Satellites can survey the Earth's surface, predict weather changes and track hurricanes. They can also help to examine resources such as xrops, forests and even minerals. Navigation satellites enable people on land or at sea to work out their exact map position, to within a few meters.