A mirage, derived from the Latin mirari, meaning 'to be astonished', is an optical phenomenon which often occurs naturally. The kind most commonly seen (known as inferior mirage, because the inverted image lies below the upright one) is produced by the refraction of light when it passes into a layer of warm air lying close to a heated ground surface). This is an example of gradient index optics.

In deserts, mirages may give the appearance of a lake or other large body of water in the distance; this is actually an image of the sky being refracted back up from the warm air lying over the sand.

On tarmac roads, mirages give the impression that distant objects are being reflected by a puddle of water on the road.

More spectacular mirages (superior mirages) are produced by a temperature inversion near eye level. In these, the inverted image lies above the upright one; and there may even be several alternating layers of upright and inverted images. These are known as the fata morgana.

Abnormally large refraction of sunlight during sunrise or sunset can produce sunrises much earlier than predicted or sunsets much later than predicted. The conditions necessary for such refraction occurs most often, but not exclusively, in polar regions where strong surface temperature inversions can be geographically extensive and homogeneous. This mirage is often called a Novaya Zemlya mirage.

Scientists say Erie mirage could be real

AP - July 31, 2006 - Cleveland, Ohio

Scientists say it's a mirage, but others swear that when the weather is right, Clevelanders can see across Lake Erie and spot Canadian trees and buildings 50 miles away. Eyewitness accounts have long been part of the city's history. "The whole sweep of the Canadian shore stood out as if less than three miles away," a story in The Plain Dealer proclaimed in 1906.

"The distant points across the lake stood out for nearly an hour and then faded away. I can see how this could be possible," said Lawrence Krauss, chairman of the Physics Department at Case Western Reserve University. Krauss and Joe Prahl, chairman of the Mechanical and Aerospace Engineering Department at Case, said mirages can occur during an atmospheric inversion, in which a layer of cold air blankets the lake, topped by layers of increasingly warm air. When this happens, it can cause the light that filters through these layers from across the lake to bend, forming a lens that can create the illusion of distant objects. The scientists said the air has to be extremely calm for the mirage to appear. If the wind blows, it distorts or dissolves the image. Prahl and Krauss said such a mirage is rare.

Tom Schmidlin, a meteorologist in the Geography Department at Kent State University, said, "It's not terribly unusual. Sailors are always exposed to this kind of thing." Prahl, who regularly sails his 30-foot sloop Seabird from Cleveland to Canada, has never seen it.

Bob Boughner, a reporter for the Chatham Daily News in Ontario, said he's seen Cleveland from across Lake Erie twice, the first time four summers ago while driving along a road near the lake. He saw it again two summer ago while driving along the same road. All of a sudden, there was Cleveland, just off the Canadian shore, as if it were just across a river, he said. "I happened to look across the lake and, geez, I couldn't believe the sight," he said. "I could see the cars and the stoplights. I could even make out the different colors of the vehicles. It lasted a good two or three minutes." Boughner said he remembers his aunt Melba Bates, who lived all her life on Lake Erie and recently died in her late 90s, talking about being able to see Cleveland, but he didn't believe her. "I thought she was making up stories," he said. "But sure enough, I could see the same damned thing. When it shows up, it looks like you can touch it."

China: Rare Mirage Lasts for 4 Hours off East China Shore

China Press - May 7, 2006

A mirage appeared off the shore of Penglai City in eastern China's Shandong Province on Sunday, May 7, 2005. Thousands of tourists and local residents witnessed a mirage of high clarity lasting for four hours off the shore of Penglai City in east China's Shandong Province on Sunday.

Mists rising on the shore

created an image of a city, with modern high-rise buildings,

broad city streets, bustling cars, and crowds of people all clearly visible.

The city of Penglai had been soaked by two days of rain before the rare weather phenomenon occurred. The mirage took place during the week-long Labor Day holiday. The small city received over 30,000 tourists on Sunday. Experts said that many mirages have been recorded in Penglai, on the tip of Shandong Peninsula, throughout history, which made it known as a 'dwelling place of the gods.' They explained that a mirage is formed when moisture in the air becomes warmer than the temperature of sea water, which refracts rays of sunlight to create reflections of the landscape in the sky.

Fata Morgana

Mirages in Finland