CHICAGO (CBS) — The Polar Vortex disturbance that has caused extreme weather in Chicago created a halo effect at sunrise over Lake Michigan on Thursday. It’s called a “sun dog.”

Ice crystals in the atmosphere refract sunlight, creating the halo and the appearance of smaller suns. With Thursday’s bitter temperatures, there were plenty of crystals in the air.

The effect is most noticeable when the sun is low over the horizon.

The temperatures this morning at 31st Street and Lake Michigan in Chicago were around minus 15. The record-setting conditions were brutal but not as bad as Wednesday morning, when minus 50 degree wind chills made it nearly impossible to be outside for more than a minute or two.