Why Is the Sky Blue

Have you ever wondered why the sky is blue? Sunlight looks white, but it is actually made of all the colors of the rainbow. When sunlight hits the tiny gas molecules in our atmosphere, blue light gets scattered in every direction. That scattered blue light is what we see when we look up.

How Light Scatters

Sunlight is made of many colors: red, orange, yellow, green, blue, and violet. When sunlight enters the atmosphere, it bumps into tiny molecules of nitrogen and oxygen. Blue light has a short wavelength and bounces around a lot. Red light has a longer wavelength and passes through more easily. The scattered blue light fills the sky.

Why Sunsets Are Red

At sunset, sunlight has to travel through much more atmosphere to reach your eyes. By the time it gets to you, most of the blue light has already scattered away. The red and orange light, which travels farther, is what is left. That is why sunsets look red and orange.

Fun Facts

• The sky on Mars looks pinkish-red because Mars has different dust particles in its thin atmosphere.
• If Earth had no atmosphere, the sky would look black even during the day, just like in space.
• Violet light actually scatters more than blue, but our eyes are more sensitive to blue.

Did You Know?

The scientific explanation for why the sky is blue is called Rayleigh scattering, named after the British scientist Lord Rayleigh who figured it out in the 1870s!