Circumhorizon Arc Above Rocky Mountain National Park

August 08, 2010


Photographer: Laura Smith
Summary Author: Laura Smith; Jim Foster

The photo above showing what looks like swatches of paint brushed across the sky was captured in Rocky Mountain National Park, Colorado, between Dream Lake and Emerald Lake. In spite of the colorful imagery the names of these lakes connote, on this day the most attention-getting colors, attributable to a circumhorizon arc (CHA), were in the sky rather than in the water. The Sun has to be more than 58 degrees above the horizon in order to see these gorgeous arcs. If oriented, hexagonal ice crystals are present in cirrus type clouds and sunlight enters though their vertical side faces and exits through their lower horizontal basal faces, a CHA may well be visible. Compare the colors shown here with those that result from a sundog, featured in yesterday's Earth Science Picture of the Day. Photo taken near noon on June 26, 2010.

Photo details: Camera Maker: Canon; Camera Model: Canon PowerShot A720 IS; Focal Length: 17.2mm; Aperture: f/5.0; Exposure Time: 0.0007 s (1/1500); ISO equiv: 80; Exposure Bias: none; Metering Mode: Matrix; White Balance: Auto; Flash Fired: No (Auto); Color Space: sRGB