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This is a Fire Rainbow, the rarest of all naturally occuring atmospheric phenomena.  The picture was captured on the Idaho/Washington border.  The event lasted about one hour.  The clouds have to be cirrus, at least 20K feet in the air, with just the right amount of ice crystals and the sun has to hit the clouds at precisely 58 degrees.

This is true as reported by Snopes.com at
http://www.snopes.com/photos/natural/firerainbow.asp

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