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Idaho's Fire Rainbow
Posted by Lev/Christopher on December 27, 2009 at 2:22am
in Science & Technology
The atmospheric phenomenon known as a circumhorizon(tal) arc, or "Fire
rainbow", appears when the sun is high in the sky (i.e., higher than
58° above the horizon), and its light passes through diaphanous,
high-altitude cirrus clouds made up of hexagonal plate crystals.
Sunlight entering the crystals' vertical side faces and leaving through
their bottom faces is refracted (as through a prism) and separated into
an array of visible colors. When the plate crystals in cirrus clouds
are aligned optimally (i.e., with their faces parallel to the ground),
the resulting display is a brilliant spectrum of colors reminiscent of
a rainbow. The example shown above was captured on camera as it hung
for about an hour across a several-hundred square mile area of sky
above northern Idaho (near the Washington border) on 3 June 2006.
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This page was created on 5 May 2010
Updated on 5 May 2010
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