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Why is the sky blue?
Name: macmillan
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
Why is the sky blue? Why is glacial ice blue? What common
properties cause them both to appear blue?
Replies:
In this case the reflected color is a measure of the size of the
centers that are scattering the light. The fact that a sunset is red and the
sky is blue indicates that the scattering centers for light are not big enough
to scatter red light, but are big enough to scatter blue light or shorter
wavelength light. Usually dust is regarded as a contributor, but molecular
sizes are also involved. I believe.
Sam Bowen
Air molecules scatter (reflect) the shorter wavelengths (violet,
blue, and green) more effectively than the other colors. As you look at the
sky the violet, blue, and green strike your eyes from all directions,
combining to make blue. Pure ice crystals also scatter light so as to give a
blue color, the purer the ice the bluer the color. Glacier ice is purer than
other ices. A sunset is red because the light is going through so much air
that the short wavelengths are scattered away and only the longer wavelengths
are bent into your eyes. Dust particles scatter all wavelengths about the
same so a really dusty sky looks white.
Mark Fernau
The reasons for why the sky is blue and why glacial ice is blue are
different. The sky is blue because the air molecules scatter the short
(violet/blue) wavelength part of the visible spectrum more strongly that
the long wavelength (red) part. For an excellent discussion, see "Colors
of the Sky," C. F. Bohren and A. B. Fraser, The Physics Teacher, May 1985,
pp. 267-272.
Glacial ice is blue because of the selective absorption by the ice of the
red part of the visible light spectrum. For a nice discussion, see the
following web site:
http://www.gi.alaska.edu/ScienceForum/ASF7/773.html
Dr. Lawrence D. Woolf
General Atomics
3550 General Atomics Court; P. O. Box 85608
Mail Stop 15/242
San Diego CA 92121-1194
General Atomics: www.ga.com/
GA Sciences Education Foundation: www.sci-ed-ga.org
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Update: June 2012
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