Sunday, December 4, 2016

Refraction Caused by a Temperature Inversion

This photo (courtesy of was taken from the Continental Divide trail, about 30 miles northwest of Helena, MT. The valleys were in the midst of a foggy temperature inversion, and a Fata Morgana (superior mirage) was present over the distant mountains. “Fata Morgana” is so-named because it is the Italian name for the Arthurian sorceress Morgan le Fay, and it was believed that she created these illusions of distant castles or land to lure sailors to their deaths. In reality all mirages are due to refraction (bending, redirecting) of light from distant objects - the strange shapes in the photo are the result of light waves from distant mountains being refracted as they traveled through layers of various temperatures (diagram). Apparently the temperature inversion that blanketed the area was one of the factors that allowed the sorceress to do her handiwork. For more about this hike (including many more photos), go to

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