All You Want to Know About Sundogs

If you are lucky, you have seen one; either a simple one or a complex one. Some claim to have seen the counterpart at night around the moon. These atmospheric and celestial phenomena depend on just the right circumstances to manifest. They also serve as the direct inspiration behind the popular and universal religious symbol of the cross and circle. The inspiration behind this ancient symbol is the sundog.

Sundogs typically form when a number of conditions are filled. The sun is typically close to the horizon at sunset or sunrise and there is a thin layer of small hexagonal ice crystals in the stratosphere within cirrus or cirrostratus clouds. Various other phenomena are associated with sundogs, but the typical sundogs form on a halo that forms as a result of light refracting through the ice crystals high in the stratosphere. The halo itself forms at about 22 degrees from the sun and the sundogs will appear as a bright circular patch on the halo that is parallel to the horizon on either side of the sun simultaneously. Sometimes, there will be a sundog above the sun as well. There may also be a tangential arc on the top portion of the halo that curves upward and away from the halo, as if to form the beginning of a second halo above the one around the sun. The sun typically has to be lower than 61 degrees from the horizon for conditions to be right for the formation of sundogs through high flown ice crystals.

Sundogs look like bright patches of light, sometimes rivaling the sun in brightness and sometimes they can be confused with comets, especially when an elongated parhelion (tail) is associated with them. As comet tails point away from the sun, an observation of a parhelion can reasonably be confused for a comet. Comets however, can be on any inclination. Parhelions are always parallel to the horizon along with the line of the sundogs and sun. They may or may not come in pairs. This depends on atmosphereic conditions which may not be uniform. Sometimes, one may notice slight color separation with the reddish part of a halo and sundog closest to the sun and the bluish part further away. Colour separation occurs only with refracted sundogs. Sometimes, sundogs and halo will be all white and this is due to the light reflecting off the snow crystals instead of refracting through them. In the case of a complex display where there are arcs above, tails on either side as well as the sundogs themselves, a mixture of various crystals with different alignments produces these phenomena at the same time. There are two basic configurations that will scatter sunlight, or moonlight into halos and sundogs with tails and crosses.

When sunlight passes through the sides of the flat hexagonal crystal, both the angle of the sun’s rays and the orientation of the crystals affects the shape and color of the sundogs. Misaligned or wobbling crystals produce colorful and elongated sundogs, while light passing through the crystal in non-optimal deviation angles up to 50° produces the "tail" of the sundog stretching away from the sun.

A line often extends through the sun to the sundogs and extends past in a long parhelion. Sometimes the sundog above the sun will also be connected with a line. This gives the appearance of a halo intersected by three crosses and the sun centered on a cross and is likely the inspiration behind the halo one often sees behind the heads of painted divinities like Jesus and the saints. As Jesus is partly derived from a solar deity, this begins to make some sense. Look carefully at a typical complex sundog complete with the rays forming crosses and you will see the three crosses that are described in the crucifixion scene. Jesus the sun deity is on the middle cross of light and the two thieves are on either side, also on crosses of light. Extending the idea of this one can see the inspiration for “the light of the world” on a cross. This vision enhances the idea of a solar deity. There is no doubt that other solar deities of the pre Christian era were also configured with a halo such as depicted in paintings of Jesus.