Saturday, January 29, 2011

floating on crystal

floating on crystal
cirrus – fragment of rainbow
mocking the sun

This patch of rainbow appeared to the right of the low sun in the west. I call these bright spots sun dogs, because they follow the sun like a dog heeling its master. Others call them mock suns, because the bright patches look like the sun behind thick clouds. These colorful spots are caused by light refracting through six-sided crystals in a thin layer of cirrostratus, producing partial halos called parhelia, from the Greek “with the sun.” Often there will be a matched pair horizontally lined up with the sun in the center of a 22 degree ring, the angle that light is bent by the the ice. Sometimes the halo itself is visible. To the observer, the ring appears to have a diameter of about two fists held at arm's length. These small, bright rainbows floating at a distance from the sun are sometimes difficult to detect, and may come and go quickly, so it's fun to catch sight of them before they fade. This one was gone in moments as the patch of cloud moved away.

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