Quirk makes Chicago skyline mirage over Lake Michigan

Joshua Super and his girlfriend, Shalee Blackmer, were enjoying a weekend of camping at Warren Dunes State Park near Bridgman on April 18, and wanted a photo of the spectacular sunset over Lake Michigan.

That's when things got weird.

On the horizon was an area of distorted shapes and columns, grouped together and almost appearing to hover over the lake, said Super, 22, an analyst for a trade advisory company from Orchard Lake.

"I wouldn't call myself a believer in aliens, but I truly thought it was something like that," he said.

It was something almost as odd: a mirage of the Chicago skyline, upside-down, from the other side of the lake — about 60 miles away.

• See original photo of Chicago skyline mirage over Lake Michigan

It's known as a superior mirage, and it's caused by a large, well-defined area of warm air over a layer of colder air that distorts light rays.

"A thermal inversion forms over the lake, bending the line of sight from the camera to Chicago back down, and producing the inverted image, which is typical of mirages," said Andrew T. Young, an astronomer at San Diego State University and a leading mirage expert.

"Normally, Chicago is hidden by the curvature of the Earth, so that it lies below the lake horizon. Here, the optical ray curvature is stronger than the curvature of the lake surface, and that brings the city's buildings into view."

Superior mirages are not uncommon at this time of the year, when the air is warming but lakes are still cold from the winter, Young said.

"The air isn't usually clear enough to make the mirage visible at this big a range; so the clarity of the air is probably the most unusual circumstance in this case," he said. "It's also helpful that the setting sun is lighting up the high clouds in the sky beyond Chicago, so that the buildings are silhouetted against the bright sunset sky."

A mirage isn't an illusion, said Alistair Fraser, an emeritus meteorology professor from Pennsylvania State University who has studied the phenomenon.

"It's an image that's created as the atmosphere acts as a lens," he said. "It's kind of a crummy lens, so the images are like a carnival fun house full of twisted mirrors — to the point that the original object has been so greatly distorted, you can't recognize what it is."

Super's photo of the mirage has received nearly 1.5 million views on Reddit. "It's all pretty cool," he said.

"I feel like I've known about Michigan and its different weather phenomena all my life, but I was completely blindsided by this."

Contact Keith Matheny: 313-222-5021 or kmatheny@freepress.com