We have had a few days this winter when the sundogs have been quite prominent in the morning and evening sky. Although not rainbows, the basic principles are similar. The scientific name for sundogs is parihelia (singular parahelion). They often appear during cold winter days when ice crystals are abundant in the atmosphere and the sun is low in the sky.
For sundogs to form the sun must be low in the sky such as around sunrise and sunset. There must also be lots of cirrus clouds between the sun and the observer in which the ice crystals, shaped like little hexagon plates, are horizontally oriented. As the sunlight passes through all those ice crystals, the light is refracted, producing the sundogs.
Sundogs will be located at 22 degrees on either side of the sun. The height of the sundogs is a function of how the ice crystals are orientated. Those little hexagon-shaped ice crystals are mostly oriented horizontally. However, greater deviations of the ice crystals from horizontal increases the vertical dimension of the sundogs. And the more the crystals wobble, the more color is produced.
So how did this interesting phenomenon come to be known as sundogs? No doubt different cultures had different explanations before the scientific explanation was discovered, but I did do a little snooping on the subject.
The term sundog may be a reference to the two sundogs following the sun, much as a dog (or in this case two dogs) follow its master. Or perhaps the sundogs are “dogging” the sun, meaning to follow, track, or hunt the sun. One Germanic version explained that the sun god Odin had two dogs [Geri (Ravener) and Freki (Glutton)] that could have been represented by the rainbows that flanked the sun on cold winter days. Sundogs have also been interpreted as a sign of the trinity (two sundogs and the sun). They have also been interpreted as two wolves hunting the sun, a sign of a coming storm, god’s wrath, or even a sign of impending good weather or good fortune.
So be on the lookout for sundogs. And if those explanations of why they are called sundogs do not suit you fancy, just get creative and make up your own explanation!