Good Question: Why is the sky blue? (explained with toast!)

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Have a piece of heavenly toast! | Stock images

Today I’ll answer one of the first questions you sent in when the Good Question feature started: Why is the sky blue?

Let’s answer this with toast! (It can be wheat or white — just don’t picture it with weird seeds and nuts. This is a good bread zone.)

You have two sticks of butter, which, for some odd reason, have been mixed with food coloring. You left the red stick in the refrigerator for hours, and the blue stick has been on your counter for the same amount of time.

You try to spread the red butter, but it’s hard and doesn’t go very far. The soft blue butter, however, spreads so easily that it covers everything. You now have a delicious piece of crunchy Smurf bread!

Sunlight is butter. And the sky is toast.

The Sun emits white light. White light, as you can prove with a prism, is actually composed of all colors. From

“As the white light from the Sun travels through the Earth’s atmosphere, it collides with particles of air. The different colors, or wavelengths, of light are scattered by these collisions by different amounts. Blue light, which has a shorter wavelength, is scattered more than red light, which has a longer wavelength.”

In other words, blue light is a soft butter that spreads (scatters) more easily than red.

This illustration from NASA visualizes the wavelengths of different colors of light.

During sunrise and sunset, the light is scattered even more because it’s passing through more atmosphere. You could say the blue butter gets spread so thin, you can now mostly see your attempts with the red butter.

Stock images

“By the time the light arrives, it’s been stripped of shorter wavelengths, which have scattered away, leaving only the longer wavelength, direct illumination of sunlight’s redder tones,” according to How

Just remember: Toast is a good idea, regardless of the color of the sky.

See NASA’s explanation for more information (on the science, not the food).

Do you have a Good Question about anything? Send it to Robert! Email him at, or visit him on Twitter @notthegeneral or Facebook.

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