Twenty Two Degree Halo
May 16, 2003
The above photo shows a portion of a classic 22 degree halo about the Sun. Notice that the inner edge of the halo appears reddish, while the outer edge is bluish. Blue light is deviated more than is red light, thus the inner edge (nearest to the Sun) is red and the outer edge is blue. Hexagonal ice crystals tumbling through the air, with no particular orientation, are responsible for halo phenomena. When light passes through randomly oriented crystals, there's a concentration of light rays deviated by angles close to 22 degrees. So in order to see a 22 degree halo, look 22 degrees away from the Sun -- about 2 fists held at arm's length.