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The solar system
The universe contains over 100 billion galaxies. A galaxy is a group of billions of stars. Our own galaxy is called the Milky Way, and it contains about 100 billion stars, including our Sun. The Sun is at the centre of the solar system.
The solar system contains different types of objects including:
- a star - the Sun
- planets, which go around the Sun
- satellites, which go around planets
- smaller objects such as asteroids and comets
Heliocentric model
People used to think that the Earth was at the centre of the universe, with everything going around it. We now know that this is not correct. The idea that fits scientific observations and allows us to predict the movement of the planets is called the heliocentric model. This just means that the Sun is at the centre of the solar system, and the Earth and other planets go around it. We say that the planets are in orbit around the Sun.
The planets in order from the Sun
Mercury to Pluto
Although scientists have discovered some extra objects orbiting the Sun that may be planets, normally we assume that there are eight planets in the solar system. In order, working away from the Sun, these are:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
If you can't remember the correct order, try this sentence, or make one up of your own:
My Very Easy Method Just Speeds Up Naming
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