Sun Dogs

Karsten left this note on my last post:



I had never heard of, much less, seen "sun dogs" before. They are beautiful. But,why are they called "sun dogs"?



Here is the photo my son Andrew took back in 2006 of sun dogs. The vertical line in the sky was due to Andrew having to piece two photos together to show the entire display.



I included Wikipedia's explanation, but they neglected to explain why "sun dogs" is their common name. Please let me know if anyone knows the reason why.

Sun dog

From Wikipedia, the free encyclopedia

A sun dog or sundog (scientific name parhelion, plural parhelia, for "beside the sun") is a common bright circular spot on a solar halo. It is an atmospheric optical phenomenon primarily associated with the reflection or refraction of sunlight by small ice crystals making up cirrus or cirrostratus clouds. Often, two sun dogs can be seen (one on each side of the sun) simultaneously.


PHYSICAL CHARACTERISTICS

[Sun dogs appear on a cold day with blizzard conditions. This photograph was taken in the evening as the sun was setting in Fargo, North Dakota. ]


Sun dogs typically, but not exclusively, appear when the sun is low, e.g. at sunrise and sunset, and the atmosphere is filled with ice crystal forming cirrus clouds, but diamond dust and ice fog can also produce them. They are often bright white patches of light looking much like the sun or a comet, and occasionally are confused with those phenomena. Sometimes they exhibit a spectrum of colours, ranging from red closest to the sun to a pale bluish tail stretching away from the sun. White sun dogs are caused by light reflected off of atmospheric ice crystals, while coloured sun dogs are caused by light refracted through them. White sun dogs are also thought to be caused by the light from the sun reflecting off of water on the ground and focusing the reflected light on the clouds above.

The ice crystals causing atmospheric phenomena are shaped as hexagonal prisms (ice Ih, e.g. with a hexagonal top and bottom and six rectangular sides). Some of these crystals are elongated, some are flat; the latter causing crisp and bright sun dogs if evenly oriented with their hexagonal ends aligned horizontally, while the former produces other atmospheric phenomena, such as parhelic circles, 22° halos, circumzenithal arcs, upper tangent arcs, and lower tangent arcs. A mixture of various crystals with different alignments produces several of these phenomena at the same time.

When sunlight passes through the sides of a flat crystal, both the angle of the sun rays and the orientation of the crystals affects the shape and colour of the sun dogs. Misaligned or wobbling crystals produce colourful and elongated sun dogs, while light passing through the crystal in non-optimal deviation angles (up to 50°) produces the "tail" of the sun dog stretching away from the sun. As refraction is dependent on wavelength, the sun dogs tend to have red inner edges while the colours farther from the sun tend to be more bluish-white as colours increasingly overlap.


When the sun is low, the two sun dogs are located on the circle of the 22° halo. As the sun rises, the sun dogs slowly move along the parhelic circle away from the sun, finally to vanish as the sun reaches 61° over the horizon(e.g. the sun dogs move from the 22° halo to the circumscribed halo).


On Earth, the first planet (counting from the sun) with significant amounts of ice crystal-carrying clouds, the pair of sun dogs flanking the sun are aligned with the horizon. On other planets and moons where water and ice are less prevalent, however, various crystal structures produce different halos. On the giant gas planets—Jupiter, Saturn, Uranus and Neptune—other crystals form the clouds of ammonia, methane, and other substances that can produce halos with four or more sun dogs.


In remote stretches of western Texas, sundog refers colloquially to a segment of a common rainbow.