Why is the sky blue?

Our earth is wrapped in a blanket of gas called the atmosphere. The atmosphere, which is the air we breathe, is made up of gases like oxygen, nitrogen, carbon dioxide, water vapour and tiny specks of floating dust.

When sunlight hits this layer, the gases spilt up the white light into its different colours. Of these different colours - red, orange, yellow, green, blue, indigo and violet, the blue is spread about the most and so appears to fill the sky.

Where there is no atmosphere, as on the moon, the sky appears to be black. Though the surface of the moon may be brightly lit, there is no gas around it to break up the passing sunlight into colours. The black sky, with all the stars and planets shining brightly, is what the astronauts see when their craft leaves the earth’s layer of gas and moves into the vacuum of outer space.