![Mountains look blue for the same reason the sky looks blue. Very distant mountains look a slightly lighter blue than medium distant ones. [NOAA]](http://www.wonderquest.com/images/2003-08-29-blue-mountains.jpg)
Q:
If you are standing in the foothills of a mountain, you see greens, yellows,
oranges, and many other colors — but, if you are about three to seven miles
away, it turns blue and all the other colors are gone. What causes this bluish
mountain? Is it a blue haze or is it a scattering of light reflected from the
mountain? Michael, Corona, CaliforniaA: We see blue low-sky light when we are far from a mountain. The farther away the mountain, the brighter blue it appears. By low-sky light, I mean the layer of air between us and the mountain.
The sky is blue because tiny air molecules of oxygen and nitrogen, water molecules, and dust motes interact with light. The small sizes of these particles means that high-frequency light (like, blue) is much more likely to interact than low-frequency light (such as red). The interaction scatters blue light in all directions. Consequently, we are more likely to see blue light than any other color. Thus, the sky looks blue.
Distant dark mountains reflect little light to our eyes. Sunlight scattered by tiny molecules between us and the mountain dominates. That’s blue low-sky light. So, the blue sky makes mountains appear blue.
Further Surfing:
WeathererQuesting: Why the sky is blue
Rod Nave, Georgia State University: Hyperphysics, Blue sky