Sun dog
From The Book of THoTH (Leaves of Wisdom)
A sun dog or sundog (scientific name parhelion) is a relatively common atmospheric optical phenomenon associated with the reflection/refraction of sunlight by the numerous small ice crystals that make up cirrus or cirrostratus clouds. Sundogs typically appear as a bright and sometimes colorful spot in the sky at a position 22 degrees to the left and/or right of the sun. They are closely related to, and sometimes appear together with, a halo. Less common associated phenomena, collectively called "ice halos," are the circumzenithal arc, upper tangental arc, parhelic circle, and lower tangental arc. There are 14 other named ice halo phenomena that could be seen given optimal conditions.
The ice crystals responsible are tiny (less than 0.5 micrometers in diameter) and hexagonal. These ice crystals refract the sunlight at an angle of about 158º, resulting in the appearance of sundogs about 22º from the sun. (180º is line of sight; subtract the 158º of refraction and the image appears at 22º.) The amount of refraction is dependent on size of the crystals, so instead of a precise, neat rainbow, stretched, pale images can appear.
Sundogs are seen in short arcs in a horizontal plane with the sun because the short, hexagonal "plate" ice crystals that make up them predominantly tumble through the sky with their flat axis oriented horizontally. The faint halo seen with the sundogs is from longer, pencil-like crystals that are at the correct orientation for their location to refract light to the eye.
Because it occurs due to internal reflection in ice crystals, it is produced only by clouds cold enough to consist entirely of ice particles rather than liquid water droplets. Such clouds are usually found only at temperatures below about -20°C. These can be seen frequently during winter cold snaps in North America and Europe, as well as at high altitudes and in the arctic regions.
Although often less vivid and more diffuse than the one depicted in the photograph, sundogs are actually rather common; they are often overlooked by amateurs because one must look in the general direction of the bright sun in order to spot them.
In remote stretches of Western Texas, sundog refers colloquially to a segment of a common rainbow.
