Why is the Sky Any Color?

“Everyone at one time or another has marveled at the beautiful red and orange colors of a sunrise or sunset. Although colorful sunrises and sunsets can be seen anywhere, certain parts of the world are especially famous for their twilight hues. The deserts and tropics quickly come to mind. Indeed, it is a rare issue of Arizona Highways that does not include at least one sunset view, and one could amass a respectable collection of the Caribbean or Hawaiian sunset postcards in just one trip.

To understand why this is so, one need only recall how typical sky colors are produced. The familiar blue of the daytime sky is the result of the selective scattering of sunlight by air molecules. Scattering is the scientific term used to describe the reflection or re-direction of light by small particles. Scattering by dust or by water droplets is responsible for the shafts of light that appear when the sun partly illuminates a smoky room or mist-laden forest. Selective scattering, also known as Rayleigh scattering (after the nineteenth century English physicist Lord Rayleigh), is used to describe scattering that varies with the wavelength of the incident light. Particles are good Rayleigh scatterers when they are very small compared to the wavelength of the light.” http://www.spc.noaa.gov/publications/corfidi/sunset/

The ancient Greek poet Homer never used a word for blue in The Odyssey or The Iliad, because blue is one of the last colors that cultures pick out a word for. In this episode, I’ll tell you not only why the sky is blue, but why it’s red at sunset. It turns out, those colors are all part of the same sunbeam. And when you’re looking at a blue sky, you could be sharing a special moment with someone thousands of miles away. Next time a kid (or the kid inside you) wants to know why the sky is blue, you’ll have science to back you up!

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