The Earth is a planet, orbiting the Sun. The Sun is a star – a giant ball of hot gas, emitting light and heat. The Sun is one of the few hundred billion stars in our Milky Way galaxy. And the Milky Way is one of the hundred billion or so galaxies in the Universe.
Astronomers have discovered that the Universe has not existed forever. It all started some 13.8 billion years ago in the big bang – a giant explosion of energy, matter, time and space. Shortly after the big bang, the expanding Universe was filled with a glowing hot gas of simple atoms. So where did all the galaxies, stars and planets come from?