We see thousands of stars twinkling in the sky at night. They seem like tiny bulbs of light. This is because they are millions of kilometres away from the Earth. In fact, these are very big balls of fire. They are made of hot gases like our Sun. Some are billions of years old. Some of the stars are very far from the Earth. Their light takes many years to reach the Earth. We cannot see the stars during the day because of the bright light of the Sun.