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Why Do Sunsets Look Red?

A beautiful red sunset, the colors warm and glowing, is one of the loveliest sights we can imagine. And sometimes, when we look at it we might say, “See how red the sun is!”

But, of course, we know that the sun itself hasn’t become red or changed in any way. It merely looks that way to us at that particular time of day. In fact, at that very moment, people are looking at that same sun thousand of miles to the west and it doesn’t look red to them at all.

What produces the colors of a sunset is the distance that the sunlight must travel through our atmosphere. The lower it is, the more of our earth’s atmosphere does that light travel through.

But first, let’s remind ourselves that sunlight is a mixture of light of all colors. Normally, this mixture of light appears as white to our eyes. But the atmosphere has molecules of air, dust, water vapor, and other impurities present in it.

As the light passes through them, different colors are scattered by these particles. Now, it so happens our atmosphere scatters out violet, blue, and green light more than it does the reds and yellows.

So when the sun is low, this scattering leaves more reds and yellows for us to see and we have a reddish sunset. By the way, this scattering of light also explains why the sky looks blue.

Violet and blue light have short waves and are scattered about 10 times more than red light waves by our atmosphere. This means that the red rays go straight through our atmosphere, while the blue waves don’t come through directly but are scattered by the air, water, and dust particles. It is this scattered light that we see as the blue sky when we look up.

Read: What Keeps the Sun Shining?