Why is the sky blue and not some other color?

Weather Blog

Dear Tom,
Why is the sky blue and not some other color?

Bill Weingarten, Chicago

Dear Bill,
Visible “white” light (electromagnetic radiation) that we perceive as sunlight consists of a range of wavelengths and a full spectrum of colors completely blended together. Each color has its own specific wavelength. The color with the shortest wavelength is scattered more by molecules of atmospheric gases and by other minute particles in the air than are other colors with longer wavelengths. In the range of wavelengths that are visible to the human eye, the color blue possesses the shortest wavelength. The blue component of sunlight is therefore scattered more than the light of other colors. This process, called selective scattering, is why the sky looks blue.

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