Lunar Halo Over Bad Mergentheim, Germany
January 21, 2010
The fish-eye view above showing a 22 degree halo around the waxing gibbous Moon was taken from my garden in Bad Mergentheim, Germany on December 26, 2009. Halos form in cirrus type clouds composed of randomly oriented, hexagonal ice crystals. The 22 degree halo results from the minimum deviation of moonlight (or sunlight) through 60 degree prisms – pencil shaped hexagonal crystals. Most moonlight as it passes through the side face of a crystal is refracted 22 degrees from the original incidence angle as it exits an alternate side face. Note that above and to the left of the halo the Pleiades star cluster is visible. The reddish star to the left of the Pleiades is Aldebaran; the brightest star in the constellation of Taurus the Bull. Compare this halo to the solar halo on the January 5, 2009 Earth Science Picture of the Day.
Bad Mergentheim coordinates: 49.485833, 9.773736