Circumzenithal Arc Over Tracy, California

October 11, 2010

Photographer: Isolde Irene
Summary Author: Isolde Irene; Jim Foster

Having a chance to see colorful arcs like the circumzenithal arc shown above should be reason enough to look up every once in awhile. This beauty was taken from Tracy, California on September 28, 2010 at 6:15 p.m. It was visible for approximately thirty minutes. The Sun was dipping toward the horizon and the circumzenithal arc was positioned nearly overhead, in command of the sky. These graceful arcs form in hexagonal ice crystals found in cirrus clouds; sunlight enters the upper basal face of the plate-shaped crystals and exits through a side face.

Photo details: f/9; 1/250sec exposure; ISO 100; exposure bias -0.7 step; focal length 28 mm.