North Cascades Circumzenithal Arc

August 31, 2008

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Photographer: Nevada Ruehlen
Summary Author: Nevada Ruehlen

This picture was taken around 7 a.m. one day in July of 2007 about 25 miles south of the Canadian border on the Pacific Crest Trail at 6,300 ft (1,920 m). The trail runs from the California-Mexico border north 2,650 miles (4,265 km) to its northern terminus about 8 miles into Canada. The day before we were hiking in light rain and that night we had freezing rain, but in the morning we had clear skies and this beautiful circumzenithal arc as the sun was coming up over the North Cascades Mountains.

Circumzenithal arcs are centered on the zenith of the sky, and can only appear if the solar angle is less than 32 degrees. For conditions to be right for a circumzenithal arc to form, small, flat, six sided ice crystals must be suspended high in the sky to create a field of tiny prisms.