Blue Mountains (Airlight)
Name: Michael B.
My question is about optics. If you are standing near the foothills of a mountain and you can see
all the trees on that mountain you see greens, yellows, oranges but if you are about 3-7 miles away
from that same mountain it turns blue and all the other colors are gone. What causes this bluish
mountain, could it be the sky color reflecting off the haze between the mountain and the person
eye or is it that the colors from the mountain scatter through the distance and since blue
scatters most it takes over. So my question is what causes a mountain to take a blue color a
blue haze in between or the scattering of light coming from the mountain?
The phenomenon you speak of is called "airlight". There is an extensive discussion of this in
John Naylor's book, Out of the Blue, A 24-Hour Skywatcher's Guide (Cambridge). Sections 1.3 -
1.5 discuss airlight, complete with pictures and diagrams, in this 2002 book.
Greatly boiled down, the molecule of the atmosphere scatter light in the blue range, and transmit
the orange range. The farther through the atmosphere you look, the more scattered light you see.
This is not the color of the "haze" between you and the mountain.
Another good conceptual physics source that is easy to read and will help you is: Paul Hewitt
"Conceptual Physics" Addison-Wesley.
---Nathan A. Unterman
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Update: June 2012