Lunar Halo and Moondog

September 25, 2010


Photographer: Geir T. Øye; Geir's Website
Summary Author: Geir T. Øye; Jim Foster

The above photo showing a lunar halo and pronounced moondog was taken from Orsta, Norway on August 23, 2010. It was snapped just before midnight when the almost full Moon was rising behind a low mountain range. Moonlight is sufficiently bright to permit halos to be observed when a veil of cirrus clouds is in the vicinity of the Moon. Ice crystals that compose cirrus clouds will form the common 22 degree solar or lunar halos as long as they're randomly oriented. Plate-shaped crystals, having a more common orientation, are responsible for the moondogs (paraselenae), which have the same altitude as the Moon and are at least 22 degrees from the lunar disk. Note the upper tangent arc at the top of the halo. The bright star at upper right is Altair in the constellation Aquila the Eagle.