What is the sky? Where is it? How high is it? What lies above it? These questions are difficult to answer, aren’t they? Is the sky blue? No, the sky has no colour. Is the sky full of air? Yes, we know that there is air all over the world. When planes fly, they need air to lift their wings. Planes can’t fly very high, because when they go higher, the air gets thinner. When we go high enough from the earth, we find there is no air. Maybe we can answer some of the questions now. What is the sky? Nothing. Where is it? It’s all round the world. The sky is space. In this space there is nothing but the sun, the moon and all the stars.