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The Color of Clouds

Wednesday, September 15, 2004
David
Lien (PSI)

Blue skies, red sunsets, and spectacular rainbows are all familiar to us. But a closer look at how sunlight interacts with the small water droplets found in clouds reveals a number of other colorful features often missed by all but the most careful observer: coronae (concentric colored rings around the sun or moon), glories (concentric colored rings around shadows cast on clouds), cloudbows and fogbows (similar to rainbows, but almost colorless), blue clouds (clouds the color of the blue sky), and my favorite, irridescent clouds. Irridescent clouds can show a wide range of colors, and any spatial organization tends to be seen in the form of rings of colors concentric about the cloud (not concentric around the sun, as seen in coronae).

I will show numerous examples of the optical phenomena described above (many taken here in Tucson) and explain the physics behind their formation with the aid of a unique graphical representation of all of the colors which can be created by sunlight passing through a spherical water drop.

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