Natural Phenomena : Parhelion/sundogs
A sun dog (or sundog) or mock sun, formally called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° halo.
Patches of light that sometimes appear beside the sun are called sundogs. The scientific name is parhelion (plural: parhelia) from the Greek parēlion, meaning "beside the sun." Speculation is that they are called that because they follow the sun like a dog follows its master. Sundogs (or sun dogs) are also referred to as mock suns or phantom suns.
Sundogs often appear as colored areas of light to the left or right of the sun, 22 degrees distant and at the same distance above the horizon as the sun. They are frequently observed on a ring or halo around the sun.
There are also moon dogs that appear alongside the moon and are formed by lunar light passing through ice crystals. Moon dogs, or paraselenae, are not observed as often as sundogs because they are visible when the moon is bright and because they appear during the night.
Sundogs are formed from hexagonal ice crystals in high and cold cirrus clouds or, during very cold weather, by ice crystals drifting in the air at low levels. These crystals act as prisms, bending the light rays passing through them. As the crystals sink through the air they become vertically aligned, refracting the sunlight horizontally so that sundogs are observed.
Sundogs, or parahelia, are bright spots in the sky caused by the refraction of sunlight off tiny ice crystals in the atmosphere. Above the Trans-Alaska Pipeline in midwinter, sundogs meld into a halo around the sun.
Sundogs frequently display a reddish tint on the side facing the sun and may sport bluish-white tails that stretch horizontally away from it. The sundog's tail is formed by light passing through the crystal at angles other than the optimal deviation angle.
Just because they are formed from ice crystals does not mean that sundogs can only be observed in cold climates. They can occur at any time of the year and from any place, although they are most visible when the sun is lower on the horizon in January, April, August and October. They also occur when ice crystals in the atmosphere are more common, but can be seen whenever and wherever there are cirrus clouds.
As the sun rises, the sundog can actually drift away from the 22-degree point. Eventually the sun rises to a higher point to where the sundog completely disappears.
Ancient Greeks came to realize that sundogs are fairly accurate rain forecasters. The ice crystals that produce the haloes and sundogs also form cirroform clouds, which make up the typical cloud formation that foretells a precipitating warm front.
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