Why is the sky blue?

 The gases and particles in the Earth's atmosphere scatter sunlight in every direction. This includes blue light, which is scattered more then the other colors because it travels in smaller and shorter waves. This is why the sky is blue most of the time.

The sky can also appear to be other colors, such as red, orange, or yellow. This is usually due to pollution or dust in the air, which can scatter sunlight differently then the gases in the atmosphere.