Scientists think that the Sun and planets grew out of a cloud of dust and gas about 4,600 million years ago. Part of this cloud collapsed and shrank and got very hot. This was the beginning of the Sun. The planets formed from the left-over gas and dust that circled the Sun.
Our Sun is a star. Stars form in enormous groups called ‘galaxies’. Our Sun is part of the Milky Way galaxy. Stars are so far apart that we use special units called ‘light years’ to measure distances between them. Light travels faster than anything else in the universe. But light takes about 80,000 years to cross from one side of the Milky Way to the other! We say the Milky Way measures 80,000 light years across.
Birth of the Solar System
These diagrams show how the Solar System probably began. The Sun formed first at the centre of the cloud. Specks of material bumped into each other and gradually built up into lumps. These grew to form the planets.
Close to the Sun, where it was hottest, rocky planets grew. They had iron at their centres. These are the ‘inner planets’. Further from the Sun, where it was cooler, giant gas planets grew. All the planets moved around the Sun.
This spiral galaxy at the top of the photo is a similar shape to our own galaxy.