Photographer: Lisa Gonnelli
Summary Author: Lisa Gonnelli; Jim Foster
The photo above showing a classic 22 degree
ice halo and a splendid
circumhorizon arc (CHA) was taken from
Pilesgrove, New Jersey on May 24, 2009, at approximately 11:25 a.m. Halos are formed by randomly oriented hexagonal
ice crystals typically found in
cirrus type clouds whereas, CHAs result from crystals having
preferred orientations. Sunlight enters through the vertical side faces and exits the lower horizontal basal faces. For CHAs, the blue side (not easily visible) is nearest to the horizon and the red side nearest the zenith. These gorgeous arcs can only be observed when the Sun is high in the sky, higher than 58 degrees above the horizon. In the mid-latitudes, look for them near noon in late spring and early summer. Note that
infralateral arcs, which can be confused with CHAs, seem to curve slightly upwards from the horizon.
