58
Sundogs - The Fact and Fiction
A sundog, or to give it its correct name, a parhelion
approximately 20 degrees of sky. Why is 22 degrees
(plural parhelia) is a well documented atmospheric
so special? It is to do with the angle that the light
phenomenon. In a similar way to how light is split by
is deflected as it passes through those hexagonal
water droplets when a rainbow forms, parhelia are
ice crystals. When the ice crystals sink through the
formed when the light from the Sun is refracted by
air and become vertically aligned, a parhelic circle
hexagonal shaped ice crystals found in cirrus clouds
is formed. If the ice crystals are arranged randomly,
high in the atmosphere. These ice crystals act like tiny
then a pair of parhelia is formed, but often the two
prisms, causing bright patches to appear either side
are present at the same time. They are usually only
of the Sun. These patches may look multicoloured,
visible when the Sun is low in the sky (below 60
but often the colours overlap so are more muted than
degrees) either at sunrise or sunset. Depending
you would expect to see in a rainbow. Sometimes the
on the conditions, there may be one or two parhe-
pair of bright patches is part of a white 22 degree ?????()?????????????????????????????????????????()???????????????M??????????????????????????????()???????????????????????????????????????()]????????????????????????????Q????????????)???????????????????????????????????????????????????????????????%??????????????????????????)??????????????????????????????????????????????)??????????????????????????????????????????????)????????????????????????????????M???Q?????)???????????????????????????????????????????????)?????e?????????????????????????????????????????????????????????????????????????????????()%
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