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Why is the Sky Blue, Space Black and Sunset Red?
by Science Made Simple

Why is Space Black?

We've all see pictures of the blackness of space. And who hasn't enjoyed a colorful sunset or sunrise? Once you understand the science behind why the sky is blue, these other questions are easy to answer.

MIT used parts of this article in their online class!
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On Earth, the sun appears yellow. If you were out in space, or on the moon, the sun would look white. Why? In space, there is no atmosphere to scatter the sun's light.

(Of course, you should NEVER look directly at the sun without adequate protection for your eyes. Regular sunglasses do NOT provide enough protection.)

On Earth, some of the shorter wavelengths of light (the blues and violets) are removed from the direct rays of the sun by scattering in the atmosphere. The remaining colors together appear yellow.

black in outer space

Why Are Sunsets Red?

As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered.

red sunset and sunrise

As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes.

The sky around the setting sun may take on many colors. The most spectacular shows occur when the air contains many small particles of dust or water. These particles reflect light in all directions. Then, as some of the light heads towards you, different amounts of the shorter wavelength colors are scattered out. You see the longer wavelengths, and the sky appears red, pink or orange.

What's in the Air?

The atmosphere is the mixture of gases and other materials that surround the Earth in a thin, mostly transparent shell. Do you know what's in the air you breathe?

READ MORE about Air & the Atmosphere →

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Easy Reading - Why is the Sky Blue?

rainbow picture

Light is a kind of energy that can travel through space. Light from the sun or a light bulb looks white, but it is really a mixture of many colors.

The colors in white light are red, orange, yellow, green, blue and violet. You can see these colors when you look at a rainbow in the sky.

The sky is filled with air. Air is a mixture of tiny gas molecules and small bits of solid stuff, like dust.

As sunlight goes through the air, it bumps into the molecules and dust. When light hits a gas molecule, it may bounce off in a different direction.

sky blue from scattered light

Some colors of light, like red and orange, pass straight through the air. But most of the blue light bounces off in all directions. In this way, the blue light gets scattered all around the sky.

When you look up, some of this blue light reaches your eyes from all over the sky. Since you see blue light from everywhere overhead, the sky looks blue.

Black sky in space

In space, there is no air. Because there is nothing for the light to bounce off, it just goes straight. None of the light gets scattered, and the "sky" looks dark and black.