Dear Tom,
It’s a little after 1 p.m. on Wednesday, May 30, and I just noticed a rainbow in a complete circle around the sun! It’s overcast but the sun is visible. What causes this?
Sally Rudman, Lombard
Dear Sally,
Several readers, including Dawn Fry in Momence and Carol Lombard, observed the same optical phenomenon, and what you saw was a solar halo.
Such halos appear when sunlight shines through ice-crystal clouds like cirrus, and they take the form of a bright white circle, usually at an angle of 22(degrees) around the sun. The dispersion of light as it is refracted by ice crystals can sometimes give solar halos red and blue coloration as well–but the halos are not rainbows, which are similar optical phenomena except that they arise from water droplets.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
