Mirage (or Fata Morgana)

A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. The word 'mirage' originated from the French se mirer ('to be reflected') and mirrors the word 'mirror'. In the end it derives from the Latin word mirus ('wonderful') and is therefore related to the word 'miracle'.

A fata morgana is an unusual and complex form of superior mirage that is seen in a narrow band right above the horizon. It is the Italian name for the Arthurian sorceress Morgan le Fay from the belief that these mirages, often seen in the Straits of Messina, between Italy and Sicily, were fairy castles in the air or false land created by her witchcraft to lure sailors to their deaths. Morgan is Welsh-name meaning 'sea-born'.
This optical phenomenon occurs when rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion. A thermal inversion is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air. This temperature inversion is the opposite of what is normally the case[1].

Fata morgana mirages significantly distort the object or objects on which they are based, often such that the object is completely unrecognizable. A fata morgana can be seen on land or at sea, in polar regions or in deserts. This kind of mirage can involve almost any kind of distant object, including boats, islands and the coastline.

A fata morgana is an often rapidly changing phenomenon. The mirage comprises several inverted (upside down) or erect (right side up) images that are stacked on top of one another. Fata morgana mirages also show alternating compressed and stretched zones.
According to folklore, the illustrious Flying Dutchman is a ghost ship that can never go home, and is doomed to sail the oceans forever. The Flying Dutchman is usually spotted from afar, sometimes seen to be glowing with ghostly light and sometimes even sailing upside down[2]. We can perhaps surmise that part of the origin of this folklore is a ship seen in a fata morgana.

[1] Van Duijnen Montijn, Pastoor, Verploegh: Maritieme Meteorologie en Oceanografie - 1975
[2] Beech: The Physics of Invisibility: The Story of Light and Deception - 2012

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