Circumhorizontal Arc photographed in Coeur d'Alene, Idaho on June 3, 2006

A circumhorizontal arc, also known as a fire rainbow, is an optical phenomenon similar in appearance to a rainbow, caused by the refraction of light through the ice crystals in cirrus clouds. It occurs only when the sun is high in the sky, at least 58° above the horizon, and can only occur in cirrus clouds. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Coeur dAlene (IPA: ) is the county seat and largest city of Kootenai County, IdahoGR6. ... June 3 is the 154th day of the year in the Gregorian calendar (155th in leap years), with 211 days remaining. ... For the Manfred Mann album, see 2006 (album). ... Full featured rainbow in Wrangell-St. ... The straw seems to be broken, due to refraction of light as it emerges into the air. ... Icicles A natural ice block in Iceland Ice is the solid form of water. ... A cirrus cloud is a type of cloud composed of ice crystals and characterized by thin, wisplike strands, often accompanied by tufts. ... Horizon. ... A cirrus cloud is a type of cloud composed of ice crystals and characterized by thin, wisplike strands, often accompanied by tufts. ...

The phenomenon is quite rare because the ice crystals must be aligned horizontally (instead of the more typical vertical alignment) to reflect. It is often thought of as the rarest natural occurrence in the world.

One particularly fine example was photographed over northwestern Idaho on June 3, 2006, and was reported in both the New Scientist and the Daily Mail (the latter under the caption "flaming rainbow"). This article or section does not adequately cite its references or sources. ... June 3 is the 154th day of the year in the Gregorian calendar (155th in leap years), with 211 days remaining. ... For the Manfred Mann album, see 2006 (album). ... New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... The Daily Mail is a British newspaper, a tabloid, first published in 1896. ...

External links

• National Geographic Photo in the News
• photograph on Coast to Coast site
• Snopes.com: Fire Rainbow
• Circumhorizon Arc
• Circumhorizon Arc Gallery
• NOAA Gallery of the event