Sun Dogs
source: http://www.islandnet.com/~see/weather/elements/sundog.htm
Many years ago, the nature-essayist Hal Borland wrote in his book Sundial of the Seasons that “Sun dogs and moon dogs are beautiful accents to a winter day or night as the rainbow is to a showery Summer day.” Sun dogs usually appear in pairs, and are loyal to the sun (as moon dogs are loyal to the moon), sitting on each side of the solar orb along a horizontal line through the solar disk. Sun dogs appear in January, April, August, and October, the month does not really matter, but they are most regularly seen close to their solar master during winter months when the sun is low in the sky and ice crystals in the atmosphere are more common, but we can see them in any of the other seasons whenever cirrus clouds fuzz the sky above.
Sun dogs on 22o halo flank South Pole sun (photo courtesy of NOAA/US Dept of Commerce).
Sun dogs, or mock suns, are technically called solar parhelia (parhelia meaning “with the sun”) and appear as bright bursts of light formed when sunlight passes through ice crystals at the proper angle. Usually, cirrus clouds in front of the sun produce sun dogs, but other ice clouds, such as ice fog and diamond dust, may also generate them. Sun dogs are sometimes so brilliant that dazzled observers mistake them for the sun. They are often bright white but may show a partial spectrum of color with the red wavelengths on the edge nearest the sun. Sun dogs often have comet-like appearance with a bluish-white tail facing away from the sun.
Sun dogs are the second most frequent halo phenomena behind the 22o halo and often accompany that halo. The difference between sun dog and halo formation is the orientation of the ice crystals through which sunlight passes before reaching our eyes. Halo formation requires a mixture of random ice crystal orientations in the sky. But if the sky has only horizontally oriented, flat ice crystals, we just see a sun dog.
Read more…
