at 6:18 PM by Jacob Wilkins

Sundogs

Sundogs were a pretty common sight across the southeastern United States this afternoon and evening. Sundogs appear as halos around the sun, although they generally do not make a complete circle. Sundogs typically appear as two subtly-colored patches of light to the left and right of the sun, approximately 22° distant and at the same elevation above the horizon as the sun.

Sundogs are commonly made by the refraction of light from plate-shaped hexagonal ice crystals in high and cold cirrus clouds or, during very cold weather, these ice crystals drift in the air at low levels, in which case they are called diamond dust. The crystals act as prisms, bending the light rays passing through them with a minimum deflection of 22°. If the crystals are randomly oriented, a complete ring around the sun is seen — a halo. But often, as the crystals sink through the air, they become vertically aligned, so sunlight is refracted horizontally — in this case, sundogs are seen.