Sundogs

Sundogs characteristically come into view as a bright and colorful patch in the sky at a position 22 degrees or more to the left and/or right of the sun. They are a halo. Other common associated phenomena, together called "ice halos," are the circumzenithal arc, upper tangent arc, parhelic circle, and lower tangent arc. There are many other named ice halo phenomena that can be seen given optimal conditions.
The ice crystals responsible are hexagonal plate shapes 0.05 - >1mm in size. These ice crystals refract the sunlight in many directions but with a minimum deviation angle of about 158°, resulting in the look of sundogs about 22° from the sun. The refraction depends on wavelength so sundogs have a red inner edge and more muted colours further from the sun as colours more and more overlap. Solar altitude is important and sundogs draw away from the sun at rising solar altitudes.
Sundogs are seen in short arcs always at the same altitude as the sun because the plate crystals are preferentially aligned by aerodynamic drag effects with their large basal faces approximately horizontal.
Although often less vivid and more diffuse than the ones depicted in the photographs, sundogs are in fact rather common; they are often overlooked 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 section of a common rainbow.