Sunday, June 07, 2015

Not a Rainbow

Not a Rainbow
At this time of year, a colorful arc often appears in the noontime sky. It looks like a rainbow, but it's not. "We saw one during Saturday's June Bug parade in Baldwin, Wisconsin," reports Craig Braymen. "This picture barely does it justice."

Braymen witnessed a circumhorizon arc--a rainbow-colored band of light caused by the sun shining through plate-shaped ice crystals in cirrus clouds. Summer is the season for circumhorizontal arcs because they appear only when the sun is high in the sky--more than 58o above the horizon. The arc's enormous size and pure spectral colors make it one of the most beautiful of all ice halos.
At medium latitudes, like much of the USA, the arc is not rare.Typically, it can be seen several times each summer. In contrast, further north in much of Europe the circumhorizon arc is a rarity and impossible to see north of Copenhagen.

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