A sun dog (or sundog), mock sun[1] or phantom sun,[2] scientific name
parhelion (plural parhelia), 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.[3]
Sundogs may appear as a colored patch of light to the left or right of
the sun, 22� distant and at the same distance above the horizon
as the sun, and in ice halos. 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 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 are
called diamond dust, and drift 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.
As the sun rises higher, the rays passing through the crystals are
increasingly skewed from the horizontal plane. Their angle of deviation
increases, and the sundogs move farther from the sun.[8] However, they
always stay at the same elevation as the sun.
Sundogs are red-colored at the side nearest the sun. Farther out the colors
grade through oranges to blue. However, the colors overlap considerably and
so are muted, never pure or saturated. The colors of the sundog finally
merge into the white of the parhelic circle (if the latter is visible). As
described in Wikipedia