Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne 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



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory