Sunrise Arc and Rays
December 12, 2003
This unusual arc is a pleasant surprise for the attentive - an upside down rainbow positioned improbably high above the sun. The picture was taken shortly after sunrise. The emanating rays clearly show the direction of the sun. Known as a circumzenithal arc (CZA), it is formed by light passing through horizontally oriented ice crystal/plates, the same type that form the more common sun dog or parhelia. They often occur together. The CZA can only be seen when the sun is less than 32 degrees above the horizon. So the next time you see a sundog, look up as well - you might see the smile of a CZA waiting to be spotted ...