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Friday, March 23, 2007
Foto Friday: Mine Eyes Have Seen the Glory
What? Friday already? Bah. Well, reflect on this:
Here's a close-up:
The colors are a bit subtle; I tried beefing them up but didn't like the result.
I didn't get to see Haleakala Crater, but I did get a nice glory out of the deal. Glories are the result of backscattering of light by water droplets. They appear when the sun is low behind the observer and the clouds below are (fairly) near. Here's a site with many glory photos, all -- harrumph! -- much better than this. Look at the links on the left for more pictures, an explanation of how glories are formed, and info on other optical phenomena. Turns out that simple reflection is not sufficient to explain the glory. Surface waves are required in order to explain the effect. That is, the light hits the surface of the water droplet, and, instead of bouncing off, travels for a short distance along its surface before being reflected. (The diagrams in the link make this clearer.)
The glory phenomenon is often seen from airplanes (see the side links at the Atmospheric Optics site). It's frequently associated with the spooky Brocken spectre (WoooOOOOooo!), and is related to heiligenschein, easily seen on a dewy morning. Like the glory and Brocken spectre, heiligenschein only appears around the position of the observer. It's sometimes referred to as "Cellini's halo", because artist (Warning! Wikipedia!) Benvenuto Cellini thought the phenomenon was a sign of his own genius.
Some people, eh? The first time I noticed the heiligenschein, I realized it was an optical phenomenon, and not anything to do with me. I guess only a great genius would make a dumb mistake like that. Reminds of the fellow who thought he had special powers, because he could make a computer monitor flicker just by humming. Turns out that the humming caused his eyes to vibrate at the frequency of the scan rate (or integral factor thereof) (these are CRTs we're talking about). (I figured this out on my own, too.) Wonder if he was a genius.
(That would be a really lame superpower, wouldn't it? Almost as lame as Turkey Volume Guessing Man. I wonder if someone's invented the League of Embarrassed Lame-Powered Superheroes. Probably. Many times over.)
If you want to make your own glories, you can get the free program MiePlot, which models Mie scattering. My inner pedant/show-off was tempted to try to simulate the glory here, but fortunately the program is a Windows program. I do not do Windows for scientific work.