We know that there is air all around the world. And we could not breathe without air. Airplanes could not fly without air. They need air to lift their wings. Airplanes can not fly very high because as they go higher the air gets thinner. If we go far enough away from the earth, we find that there is no air.
What is the sky? Nothing. Where is it? It is all around the world. The sky is space. In this space there is nothing except the sun, the moon and all the stars.
The moon is about 384,000 kilometers away from the earth. An airplane cannot fly to the moon because the air reaches to an altitude of only 240 kilometers. Then there is no air. But there is something that can fly even when there is no air. It is a rocket.
How does a rocket fly? If you want to know, get a balloon and blow it up, until it is quite big. Do not tie up the neck of the balloon. Let go! The balloon will fly off through the air very quickly. The air inside the balloon tries to get out. It reaches out through the neck of the balloon and this pushes the balloon through the air. It does not need wings like airplane.
