Why is the sky blue?

Sunlight looks white. It contains all colors: red, orange, yellow, green, blue, indigo, violet. Light travels as waves. Different colors have different wave sizes. Red light has long, wide waves. Blue light has short, choppy waves.

Earth has an atmosphere. It is a layer of gases around our planet. This layer contains tiny molecules of nitrogen and oxygen. When sunlight hits the atmosphere, the light strikes these molecules.

Long red waves pass through the atmosphere easily. They go straight to your eyes. Blue waves are different. They hit the gas molecules and scatter in every direction. This scattering sends blue light all over the sky. When you look up, your eyes catch this scattered blue light from every part of the sky.

Why does the sky turn red at sunset?

When the sun is low, light travels through more atmosphere to reach you. The blue light scatters away completely before it reaches your eyes. Only the long red and orange waves pass through. This makes the sunset look warm and colorful.

Science explains our world. Light, atmosphere, and scattering create the beautiful blue sky we see every day.

What color is the sky on a cloudy day?