Sun dog
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Sun_dog_-_wea00148.jpg
A sundog 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. Sundogs are closely related to, and sometimes appear together with, a halo. The scientific name for the phenomenon is parhelion (Plural parhelia). 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 -40°C. Except in polar regions, such cold temperatures are usually found only at fairly high altitudes (typically well above 7,000 m in the middle latitudes). Sundogs (and other associated phenomena such as sun pillars) are common in Antarctica.
Although weak sundogs are actually rather common, they are often overlooked by laypeople because one must look in the general direction of the bright sun in order to spot them.
In remote streches of Western Texas, sundog refers colloquially to a segment of a common rainbow.
External links
- http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/ice/sd.rxml
- http://www.astrophys-assist.com/wilobs/weathwin/sundog.htm
- http://www.sundog.clara.co.uk/atoptics/phenom.htm