Why Is The Sky Blue?

In order to understand why the sky is blue, you must first learn a bit about the properties of light. While the light from the Sun or an artificial source such as a light bulb may look white, it's actually composed of many colors. A rainbow displays those colors by splitting the light through water droplets in the air. All of those colors, when combined, appear to be white.

You've probably heard the term "light wave". Each of the colors that make up the white light have a different wavelength. It's not necessary that you totally understand this in order to understand why the sky is blue. Just so you know that the different colors have different properties (wavelengths).

Waves can be affected by the world around them. Light waves can be reflected. That's why you can see your "reflection" in a mirror. Light waves are reflected off your face, then reflected off the mirror's surface, and then back to your eyes and you see yourself!

Waves can also be absorbed. Light waves can be absorbed by the gas molecules in Earth's atmosphere. We mentioned earlier that the different colors in light have different wavelengths. Some wavelengths are absorbed by the atmosphere better than others. Therefore, some of the colors pass through the atmosphere (sky) and some are absorbed.

The color whose wavelength is most readily absorbed just happens to be blue! The other colors of sunlight pass straight through the atmosphere and illuminate the surface of the Earth and everything on it. The blue light, however, after being absorbed by the gas molecules, re-radiates away from them in all directions. So when you look at the sky, it is literally "shining with blue light".

To put it in very simple terms ... the sky is blue because it absorbs the blue light from the Sun while letting the other colors pass through.

So what makes a sunset look red or orange? Is the atmosphere absorbing orange lightwaves? The answer is no. The same effect that causes the sky to be blue causes a sunset to appear red or orange. Let's look at how that occurs.

When you look at a sunset, you're not looking at the sky ... you're looking at the Sun. You're seeing the light waves that are least absorbed by the molecules in the atmosphere. The ones that pass through and make it to your eyes. The color that is least absorbed just happens to be red. As the Sun gets lower and lower in the sky, its light passes through more and more of the atmosphere before reaching your eyes. That results in not only more and more of the blue light being absorbed ... the molecules start absorbing more and more of the other colors too. If you see the sunset in the flatlands where its light is passing through a maximum amount of atmosphere, all of the lightwaves are being absorbed more and more than the red ones. That's why the color of the sunset changes as it gets lower in the sky!

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