Weatherz School: Why the sky is blue

Anyone who has ever put an eye to the sky can tell you that it’s blue. It’s a basic fact of life. But what isn’t as obvious is the reason why.

With water making up over 70% of the Earth’s surface, a common misconception is that the sky is blue because it reflects our oceans. The actual source of the blue color has nothing to do with water and everything to do with light.

The sun emits white light which is made up of all the colors of the rainbow. As light approaches the earth, it encounters air molecules about 18 miles above the surface. Each color has its own wavelength. Air molecules are just the right size to help scatter blue and violet wavelengths.

Meanwhile, the rest of the colors continue down to the surface. That leaves blue light as the one that’s scattered from molecule to molecule until it’s reflected at you from all parts of the sky.

But skies aren’t only blue. Sunrises and sunsets can provide brilliant displays of pinks, oranges, and reds. That’s because sunlight has further to travel to reach your eye as it nears the horizon.

With blue and violet light having shorter wavelengths, they’re most likely to be scattered by air and dust particles. As the distance increases, it’s the long wavelength colors that make it through unscattered.

So next time you take in the stunning view of the sky and its colors, thank the sunlight and the stuff in the atmosphere that breaks it up.