A satellite is a small body revolving around a plane. The moon is a satellite of the earth. As the earth revolves in its orbit around the sun, the moon revolves around the earth.
The satellites of other planets are also known as ‘moons’. Earth has only one moon, whereas Saturn has nine, Jupiter has twelve, Mars and Neptune have two each and Uranus has five. The only planets no moon are known are Mercury, Venus and Pluto. Thus, Jupiter has maximum number of moons.
The satellites, like planets, have no light of their own. They shine by reflecting the light of the sun. A satellite is held by the gravitational force of the planet and revolves around it. Now let us study in somewhat detail, the earth’s satellite, the moon.
Moon – the earth’s Satellite
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Our moon is about 3.86* 105 Kilometres away from the earth and is about 3476 kilometres in diameter. It takes 271/3 days to complete one revolution around the earth. Because of its small size the moon’s gravitational force is only one-sixth as great as the earths and the moon is unable to hold gases. Its surface has large number of cracters and mountains and is covered with hard and loose dirt. On the moon, days are very hot while nights are very cold. The large temperature variation is due to the absence of atmosphere on the moon. The atmosphere acts as a blanket by absorbing radiations and keeps the body warmer. Since the moon is closer to the earth, it appears to be much bigger than the stars.
In addition to plants and satellites, the solar system contains a large number of small objects that are held in the orbit by the sun’s gravity. These are –asteroids, meteors and comets. These bodies have negligible mass as compared with planets.