What Is The Definition Of A Planet?

The planets are large bodies, like the Earth, that revolve around a star – in our case, the Sun. Planets do not give off light of their own but they reflect light from the Sun. Including the Earth, there are nine planets in the solar system – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

The planets were first observed by the ancient Greeks who saw points of light that seemed to move backwards and forwards against the background of apparently fixed stars. It was the Greeks who gave the planets their name, from a Greek word meaning 'wonderer'.

Jupiter is the largest of the planets in our solar system and is about 1000 times bigger than Earth. It has twelve moons and is formed mainly of a ball of gas. Like Earth, Venus, Mercury and Mars are solid planets with a dense core. Unlike Earth, none of the other planets support life.