Dear Tom,
Why is the sky blue? Does it reflect the color of lakes and oceans?
Kathrine Ciprano
Dear Kathrine,
Our magnificent blue sky results not from reflection of light but rather from a phenomenon known as preferential scattering of sunlight. Pure sunlight consists of a mix of all the colors of the spectrum blended together into white light, and each color has its own specific wavelength.
As sunlight passes through the atmosphere to our eyes, the molecules of nitrogen and oxygen, the two gases that make up 99 percent of the atmosphere, separate (“scatter”) the white light into its component colors. However, this happens much more so for the shortest wavelength color, which is blue, than for the other longer-wavelength colors. Blue light is preferentially scattered, and that is primarily what reaches our eyes.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Pl., Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
