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Path: utzoo!watmath!clyde!akgua!sdcsvax!sdcrdcf!hplabs!sri-unix!Craig.Everhart@CMU-CS-A.ARPA
From: Craig.Everhart@CMU-CS-A.ARPA
Newsgroups: net.physics
Subject: Re: Clouds
Message-ID: <12241@sri-arpa.UUCP>
Date: Fri, 13-Apr-84 04:08:00 EDT
Article-I.D.: sri-arpa.12241
Posted: Fri Apr 13 04:08:00 1984
Date-Received: Sat, 12-May-84 07:21:14 EDT
Lines: 17

Just in case the backlog of mail doesn't catch this one.  Bill Jefferys'
answer about the Green Flash verges on correcting some earlier mis-statement
about sunsets being red because the photons lose energy passing through the
atmosphere.  Not as I understand it!  The atmosphere preferentially scatters
the higher-energy (more blue) photons to the side (90 degrees from the
original direction of travel), and preferentially allows lower-energy
(redder) photons pass through undisturbed.  Other media will do this, also;
my college E&M professor showed this to us with a flashlight beam through
milky water.

This phenomenon alone will never produce other than reddened sunsets and
blue skies--and as a bonus, explains why the sky is the richest blue
when you look at the part 90 degrees away from the sun.  The Green Flash
needs the atmospheric absorption in order to work, not just scattering.
(As Jefferys' submission explains.)  I just couldn't bear to let people
think that sunsets were red due to ``energy loss of the photons passing
through the atmosphere.''