A Fata Morgana (Italian: [ˈfaːta morˈɡaːna]) is a complex form of superior mirage that is seen in a narrow band right above the horizon. It is an Italian term named after the Arthurian sorceress Morgan le Fay, from a belief that these mirages, often seen in the Strait of Messina, were fairy castles in the air or false land created by her witchcraft to lure sailors to their deaths.[citation needed]
Although the term Fata Morgana sometimes is applied to other more
common kinds of mirages, true Fata Morgana is different from both an
ordinary superior mirage and an inferior mirage.
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 may be seen on land or at sea, in polar
regions, or in deserts. It may involve almost any kind of distant
object, including boats, islands, and the coastline.
Often, a Fata Morgana changes rapidly. The mirage comprises
several inverted (upside down) and erect (right side up) images that are
stacked on top of one another. Fata Morgana mirages also show
alternating compressed and stretched zones.[1]
The optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed.[1]
(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; air is usually warmer close to the surface, and cooler higher up.)
In calm weather, a layer of significantly warmer air may rest
over colder dense air, forming an atmospheric duct that acts like a
refracting lens,
producing a series of both inverted and erect images. A Fata Morgana
requires a duct to be present; thermal inversion alone is not enough to
produce this kind of mirage. While a thermal inversion often takes place
without there being an atmospheric duct, an atmospheric duct cannot
exist without there first being a thermal inversion.