The WGN Weather Center received several photographs Friday of a colorful sky display. The pictures were showing an optical display called a circumhorizontal arc. It is caused by the refraction of light through ice crystals in cirrus clouds. It con only occur when the sun is high in the sky at 58º or higher above the horizon which at Chicago’s latitude can only occur from about mid April to late August.

Thanks to Dr. Craig Bohren at Penn State for helping us identify this beautiful optical phenomenon.

Photo by Maryan Olney from Matteson

Photos by Renee Clingen of Tinley Park