Why the Sky Is Blue

Look up on a clear day. What color do you see? Bright blue. But why? The answer is light and air.

Sunlight looks white to us. In truth, sunlight has all colors of the rainbow. Red, orange, yellow, green, blue, purple. These colors travel in waves. Some waves are long. Some waves are short. Red waves are long. Blue waves are short.

Earth has air all around it. The air is full of tiny things like gas, dust, and water drops. When sunlight reaches Earth, it hits the air.

Long waves, like red and yellow, pass right through the air. They do not stop.

Short waves, like blue, hit the air and bounce in all directions. They scatter everywhere. When you look up, you see this scattered blue light.

Why not violet? Violet waves are even shorter than blue waves. They scatter even more. But human eyes are more sensitive to blue light than violet light. Our brains see the sky as blue.

What about sunset? When the sun goes down, the light must travel through more air to reach your eyes. Most of the blue light scatters away before it gets to you. Only the long red and orange waves reach your eyes. That is why sunsets are red and yellow.

Science explains the world around us. Light, air, and our eyes work together to paint the sky.

What color is the sky on Mars?