Halo

From Encyclopediak

Halo, a general term used to designate a variety of luminous appearances in the sky. Halos appear to be rings about the sun or moon, and are believed to be due to diffraction or scattering, by particles of moisture, of the light in the atmosphere. The halo around the moon is thought to be due to refraction of the light. These halos are commonly called coronas. Sun halos seen in the Arctic regions are due to the refraction of light by the ice crystals of cirrus clouds. These halos sometimes have the appearance of circles within circles intersected by vertical or horizontal lines of light. At the points of intersection, bright spots appear, which are called mock suns or sun dogs.