Why is the sky blue? - Weather Science
Welcome to Quatr.us Study Guides!

Atmosphere

blue sky

This is an easy question to ask but the answer is pretty hard. The light that comes from the Sun to Earth looks white, but really it is made up of all different colors of light mixed together. You can see this by using a glass of water or a glass prism to break up sunlight into rainbows.

rainbow

In the rainbow, red is on the outside and blue is on the inside. That's because red light travels in long, slow waves and blue light travels in short, quick ones. As the Sun's light travels through the air to get to your eyes, many of the light waves hit molecules of (mostly) oxygen and nitrogen in the air. These molecules soak up the light energy, but mostly the blue light because it has shorter wavelengths and is more likely to hit them. Then they shoot out that light energy again, but in all different directions so it gets scattered all over, and you see it all over the sky.

Meanwhile, the longer wavelengths of light - red, yellow, orange - don't get absorbed so much. More of them make it in a straight line from the Sun through the air to your eyes. That's why the Sun looks yellow to you.

But violet - purple - moves in even shorter waves than blue. Why doesn't the sky look purple? It's true that the air molecules do scatter the purple light even more than the blue light. But 1) the sun actually puts out less violet light than blue light, 2) our eyes are not as good at seeing the color purple as we are at seeing blue, and 3) the scattered light we actually see in the sky is mostly blue, with some violet on one end and some green on the other end. The violet and green cancel each other out so we see blue.

Learn by doing: scattering blue light
Learn by doing - atmosphere
More about the atmosphere

Bibliography and further reading about the atmosphere:

Learn by Doing - Clouds
More about clouds
More about Thunderstorms
More about Weather
Quatr.us home


Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram, Pinterest, or Twitter, or buy her book, Vandals to Visigoths.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter, or buy her book, Vandals to Visigoths.
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Check out our new ebook: Short and Simple: Ancient Greek Myths! - just out! Twenty-five easy to read, illustrated stories, from Pandora to Medea, Icarus, and the Trojan Horse (you can read these online as samples). Get it this week for just $14.99, five dollars off the regular price of $19.99.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Quatr.us Study Guides
  • Publisher: Quatr.us
  • Date Published:
Did you find what you needed? Ask your teacher to link to this page so other people can use it too! Send it in and win a Quatr.us "Great Page!" award!
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article
Quatr.us is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Quatr.us Study Guides, . Web. 19 September, 2017
ADVERTISEMENT