Why Is The Sky Blue? - National Geographic Kids

Skip to contentSearchShopGamesQuizzesPersonality QuizzesPuzzlesActionFunny Fill-InVideosAmazing AnimalsWeird But True!Party AnimalsTry This!AnimalsMammalsBirdsPrehistoricReptilesAmphibiansInvertebratesFishExplore MoreMagazinehistoryScienceSpaceU.S. StatesWeird But True!Subscribemenu

Please be respectful of copyright. Unauthorized use is prohibited.Juice Images Ltd / Getty

Actually, the sky was orange until about 2.5 billion years ago, but if you jumped back in time to see it, you’d double over in a coughing fit. Way back then, the air was a toxic fog of vicious vapors: carbon monoxide, carbon dioxide, nitrogen, cyanide, and methane. This last gas gave the sky an orange tint and the land a strange glow. But then something happened that would change the sky—and the planet—forever.

Blue-green microbes called cyanobacteria formed in the ocean that were capable of a special trick that transformed the planet: photosynthesis. Later used by plants, this natural process converts sunlight and carbon dioxide into energy, creating oxygen as a by-product. Fed by nutrients in the sea and powered by the sun, cyanobacteria exploded across the ocean, pumping more and more oxygen into Earth’s atmosphere. Slowly, over the next two billion years, oxygen in the atmosphere rose to its present levels, and the sky took on the blue hue on view today.

So why is the sky blue?

The light shining from the sun is made of all the colors of the rainbow, and each color travels on its own special type of wave, called its wavelength. When light hits the air molecules in our atmosphere, its colors are scattered in all directions. Blue light is scattered more because of its short, choppy wavelength, making it the color we see the most. At sunrise and sunset, when the sunlight must travel though a thicker chunk of atmosphere to reach our eyes, blue light is scattered completely out of our field of vision, and we’re typically left seeing brilliant red and orange colors.

Text adapted from the Nat Geo Kids book Why Not?, by Chrispin Boyer, boy running photograph by Juice Images Ltd / Getty

Explore more

Weird But True!

Check out Weird But True! videos, fun facts, and more.

(AD) Why Not?

Why do I get sleepy?

Like all animals, our bodies follow a 24-hour schedule known as a circadian rhythm, sort of an internal alarm clock that keeps time by tracking light and darkness.

Why can't I eat cupcakes for dinner?

Dessert for dinner sounds like a miracle meal plan. But is it enough?Legal

• Terms of Use
• Privacy Policy
• Your California Privacy Rights
• Children's Online Privacy Policy
• Interest-Based Ads
• About Nielsen Measurement
• Do Not Sell My Info

Our Sites

• National Geographic
• National Geographic Education
• Shop Nat Geo
• Customer Service

Join Us

• Subscribe
• Manage Your Subscription

Copyright © 1996-2015 National Geographic SocietyCopyright © 2015-2026 National Geographic Partners, LLC. All rights reserved