Lunar Halo Over Cascade, Colorado
May 07, 2009
The above photo of a gauzy 22 degree lunar halo was taken from Cascade, Colorado on November 10, 2008, at approximately 9:00 p.m. Mountain Standard Time. These often conspicuous rings form when moonlight is refracted by randomly oriented, hexagonal ice crystals that compose cirrus clouds. It's the pencil shaped or columnar crystals that are responsible for halo formation. These crystals are aligned horizontally with their long side faces between the observer and the Moon or Sun. Moonlight enters one of the side faces and is refracted 60 degrees through an alternate side face. Though a halo has little color compared to rainbows and specialized arcs, even at night the inside of the ring can be seen to have a reddish hue.