Diamond Dust Dog

March 03, 2003


Provided by: David J. van Unen
Summary authors & editors: David J. van Unen; Les Cowley

At first glance, this tall, brightly colored arc, seemingly suspended in front of the distant trees and tanks, looks like a rainbow. However, it was much too cold for rain (temperature near -18 C or 0 F). The inset photo reveals that this arc is actually an unusual sundog or parahelia. Sundogs form when hexagonal, plate-shaped ice crystals are oriented with their flat faces nearly horizontal. When this sundog appeared at Fort St. John, British Columbia, Canada, the sky was clear, but ice crystals were floating in the air - the crystals weren't associated with clouds. These type of falling crystals are called "diamond dust," because the air sparkles and glitters as though dusted with diamonds. To make this exceptionally tall sundog, the plate-shaped "diamonds" must have been quite large, and they likely were rather wobbly as they slowly descended in the cold, still air.

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