A fata morgana (after the Italian translation of Morgan le Fay, the fairy shapeshifting half-sister of King Arthur) is a mirage, an optical phenomenon which results from a temperature inversion.
Fata Morgana is most common in polar regions, especially over large sheets of ice with a uniform low temperature, but it can be observed almost anywhere. While in polar regions Fata Morgana is observed on cold days, in deserts and over oceans and lakes Fata Morgana is observed on hot days. In this form of mirage, images which would normally be concealed behind the horizon appear distorted in the sky.
A fata morgana is caused by abrupt variances in air temperature; when air above the line of sight is warmer than the air below. This is known as temperature inversion, since it does not represent the normal temperature gradient of the atmosphere. Light traveling from the horizon is refracted towards the earth, away from the warmer air above. These are the conditions which cause a superior mirage - a Fata Morgana occurs only when light travels through multiple distinct temperature gradients. This results in an image which may be compressed in some sections and expanded in others. As air temperature changes over time so do the various angles of refraction, causing the image to expand or contract as the atmosphere returns to its standard temperature gradient.
The first mention of the "Fata Morgana" phenomenon in English was in 1818, when this type of mirage was observed in the Strait of Messina, between Calabria and Sicily.
In the children's book The Thirteen and a Half Lives of Captain Bluebear by German novelist Walter Moers; the principal character, Bluebear, whilst travelling through a desert with a tribe of social dropouts, encounters a semi-stable Fata Morgana that moves as far away from whatever is moving towards it does, at precisely the same speed. Hence it remains constantly in the distance. In the English version, the mirage is named "Anagrom Ataf": Fata Morgana spelt backwards.
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