Weather Explainer: Sundogs

Photo courtesy Cotton Ketchie
Photo courtesy Cotton Ketchie

CHARLOTTE, NC (WBTV) - Check out this picture sent in by one of our viewers taken over Mooresville Sunday morning.  What you're looking at is called a Sundog. 

These Sundogs, also called mock suns or parhelia, appear as a colored patch of light to the left or right of the sun.  They always appear at the same elevation as the sun, and can be reminiscent of a oval, compact rainbow, with the red color nearest to the sun.

Sundogs form when light is refracted at a 22° angle off of plate-shaped hexagonal ice crystals in high level cirrus clouds.  Clouds made of liquid water will not produce this effect.  You're most likely to see one when the sun is low.  

As the sun gets higher in the sky, the rays pass through the ice crystals at a larger angle, and the sundogs move farther from the sun.  

Sundogs will form if the hexagonal ice crystals are oriented with the flat faces horizontally.  If the crystals are skewed, a halo will form around the sun instead.