Circumzenithal Arc


No, this is not a photo of a rainbow turned upside down! It's a halo phenomenon called a circumzenithal arc, which is caused by sunlight refracting off ice crystals high in the atmosphere. This colorful arc appears about 50 degress above the sun, when the sun is less than 32 degrees above the horizon. As the name implies, the arc is centered on the zenith, and since it appears so high in the sky it frequently goes unnoticed. In this photo, I've adjusted the contrast and saturation slightly to make the arc more plainly visible.

Date: April 26, 2004
Time: 5:32pm MST
Location: Phoenix, Arizona
Camera: Olympus OM-1 35mm SLR
Film: Kodak Ektachrome E200 Professional slide
Focal length: 50mm with polarizer
Aperture: f/8-11
Exposure time: 1/125 second
Scanner: Nikon Coolscan LS-2000

Revised: December 26, 2004
Copyright © 2004 Joe Orman
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