Dear Tom,
Looking at the sky recently, this question came up: Why is the sky blue and not some other color?
Daniel Sommers, Western Springs

Dear Daniel,
Visible “white” light that we perceive as sunlight consists of a range of wavelengths and a full spectrum of colors blended together, but actually each color has its own specific wavelength. The color with the shortest wavelength is scattered more by molecules of atmospheric gases and other minute particles in the atmosphere 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 appears blue.