Circumzenithal Arc Above Prague

March 18, 2006


Provided and copyright by: Tomas Trzicky
Summary authors & editors: Tomas Trzicky

The photo above shows a brilliant circumzenithal arc, one of several halos and arcs observed during a spectacular halo display in Prague, Czech Republic, on February 3, 2006. This lovely arc was accompanied by bright mock suns (sundogs) and fragments of the parhelic circle. Circumzenithal arcs can be viewed when the Sun's elevation is lower than 32° above the horizon. Hexagonal plate-shaped ice crystals having a preferred orientation are responsible for these arcs. Their vivid colors are produced by the refraction of light rays passing through the 90° prisms of the oriented plates -- light enters upper horizontal faces and passes out through vertical sides.

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