National Science Foundation A sun dog on the right side of a halo around the sun. The globe blocking the sun is atop a pedestal marking the Ceremonial South Pole. A sun dog is a rainbow-like spot in a cirrus cloud. Light shining through ice crystals in the cloud makes a sun dog, much like light shining through raindrops makes a rainbow.
Ice can take on many forms and shapes.
The cloud ice, however, is shaped like hex bathroom tiles or stubby pencils each no bigger than the tiniest grains of sand. The horizontal crystals bend the light 22 degrees, say Lynch and Livingston, as the light enters and exits the crystal. Light colors fan out from the bending and display as a sun dog Sun dogs are among the most commonly seen sky phenomena, appearing most prominently when the sun is low. Hold your arms straight out to estimate the two handbreadths.