Why is the sky blue and sunsets red?
Sunlight contains every color. Air molecules scatter blue light much more than red, so blue light bounces around the whole sky. At sunset, light travels through so much air that most of the blue is scattered away, leaving reds and oranges.
Sunlight is every color at once
The light from the sun looks white, but it’s really a mix of all the colors of the rainbow. Each color travels as a wave with its own length, blue short and red long.
Share this stepAir bounces blue light everywhere
When sunlight hits the tiny molecules in our air, the short blue waves get scattered in all directions, far more than red. That scattered blue reaches your eyes from every part of the sky.
Share this stepAt sunset, only red makes it through
When the sun is low, its light crosses much more air to reach you. Along the way almost all the blue is scattered off to the side, so the light that gets through is mostly orange and red.
Share this stepSame sunlight, different path.
Sunlightairblue day, red evening
The sky isn’t blue because air is blue. It’s blue because air sorts the colors of sunlight, sending blue toward you from everywhere overhead.
Common follow-up questions
If violet light scatters even more, why isn’t the sky violet?
Sunlight contains less violet than blue, some is absorbed high in the atmosphere, and our eyes are much more sensitive to blue.
Why is the sky black in space?
There’s no air in space to scatter sunlight, so no light bounces toward your eyes from the empty sky around you.
Why are some sunsets more colorful than others?
Dust, smoke and tiny water droplets add extra scattering. After wildfires or volcanic eruptions, sunsets can be especially deep red.
Why are clouds white?
Cloud droplets are much bigger than air molecules and scatter all colors about equally, and all colors together look white.
