Peeking Sun Halo

A setting sun produced this partial halo effect looking west from Bowman Woods Park in Cedar Rapids, Iowa at 7:00 PM, Saturday, September 1, 2012. The sun was 6 degrees above the horizon at this moment and sunset was at 7:37 PM CDT. When conditions are right water vapor in the frozen upper atmosphere condenses into tiny hexagonal ice crystals which catch the sunlight and bend it, like tiny prisms. Because of the sun's low position in the sky and a cover of trees, only the upper part of the halo was visible.