Regular sky watchers are accustomed to seeing rings of light around the sun. Called "ice halos," they form when sunlight shines through ice crystals in high clouds. Usually these rings appear one at a time. On June 21st, Jun Lao of Mason, Ohio, saw three at once:
"It was about 4 p.m. EDT in the greater Cincinnati area when I imaged what I first thought was a regular halo, but was surprised to see three concentric halos!" says Lao. "The sky had a light cloud layer, and I suspect these multiple halos were caused by pyramidal ice crystals."
Indeed, they were. Ordinary sun halos are produced by crystals shaped like pencils and flat plates. On rare occasions, however, the sky fills with pyramidal crystals. They look like two pyramids glued together, base-to-base. The pyramid-tips are sometimes truncated, and sometimes the two pyramids are separated by an intervening prism section, creating 18 different variations with up to 20 sides. Such a complicated crystalline form can produce multiple halos during the same display.
These multiple halos are sometimes called "odd-radius halos." However, as atmospheric optics expert Les Cowley points out, "Odd radius halos are perhaps not so 'odd' or rare as usually thought. Make a point of routinely searching for them."
http://spaceweather.com/
Indeed, they were. Ordinary sun halos are produced by crystals shaped like pencils and flat plates. On rare occasions, however, the sky fills with pyramidal crystals. They look like two pyramids glued together, base-to-base. The pyramid-tips are sometimes truncated, and sometimes the two pyramids are separated by an intervening prism section, creating 18 different variations with up to 20 sides. Such a complicated crystalline form can produce multiple halos during the same display.
These multiple halos are sometimes called "odd-radius halos." However, as atmospheric optics expert Les Cowley points out, "Odd radius halos are perhaps not so 'odd' or rare as usually thought. Make a point of routinely searching for them."
http://spaceweather.com/
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