Why is the sky blue?

On a clear day, the sky is blue. At sunset, it turns orange and red. Both colors come from the way air scatters sunlight.

Sunlight looks white, but it is a mix of all the colors of the rainbow. Each color is a light wave with its own length. Blue waves are short, and red waves are long.

When sunlight hits the air, tiny air molecules send some of it off in all directions. Short waves are scattered much more than long ones. Blue light is scattered about five times more than red.

So blue light reaches your eyes from every part of the sky. Wherever you look, you see blue.

Violet waves are even shorter than blue ones. But sunlight contains less violet, and our eyes are more sensitive to blue.

At sunset, the light travels through much more air to reach you. Most of the blue is scattered away on the way. The oranges and reds are what is left.

So the sky is blue because air scatters short blue waves much more than long red ones.