A Sun dog or sundog is an atmospheric phenomenon that creates bright spots of light in the sky, often on a luminous ring or halo on either side of the sun. They can be seen anywhere in the world during any season, but they are not always obvious or bright. Sundogs are best seen and are most conspicuous when the sun is low. Sundogs are made commonly of plate-shaped hexagonal ice crystals in high and cold cirrus clouds or, during very cold weather, by ice crystals called diamond dust drifting in the air at low levels.
These 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.
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