Satellite can be divided into following types.


Natural and Artificial Satellite

1. The celestial bodies which revolve around the planets in close and stable orbits, are called as Satellite.

2. Our solar system consists of a sun which is stationary at the centre of the universe and nine planets which revolve around the sun in separate orbits. The nine planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Each of these planets may be called a satellite of the sun. These planets too have got satellites revolving around them. Whereas mercury, Venus and Pluto do not have any satellite, the earth has one, mars and Neptune two each, Uranus five, Saturn ten and Jupiter has twelve. These celestial bodies moving around a planet are called “natural satellites”. Thus, the earth, in an almost circular orbit of radius 3.84 × 105 km.

3. Artificial satellite

These satellites are launched from the earth so as to move around it. A number of rockets are fired from the satellite at appropriate times of establish the satellite in the desired orbit. Once the satellite is placed in the desired orbit with the correct speed for that orbit, it will continue to move in that orbit under gravitational attraction of the earth.

4. Geostationary satellite

Our earth rotates about its own axis (the line joining the North Pole and the South Pole) once in 24 hours. Suppose a satellite is established in an orbit in the plane of the equator. Let the height of the satellite is such that its time period of revolution is 24 hours and it moves in the same sense as the earth. Such a satellite will always be overhead at a particular place on the equator. As seen from the earth, this satellite will appear to be stationary. Such a satellite is called geostationary satellite. These satellites are used for telecommunication, weather forecast and other useful purposes. The radius of geostationary satellite comes out to be 4.2 × 104km i.e., its height above the earth’s surface is about 3.6 × 104 km.