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Fata Morgana (mirage)
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Optical phenomenon
A Fata Morgana seen over the Baltic Sea, 2016. The mirage consists of multiple upright and inverted images over the original object.<br>A Fata Morgana of a container ship seen off the coast of Oceanside, California<br>A Fata Morgana changing the shape of a distant boat<br>A Fata Morgana (Italian: [ˈfaːta morˈɡaːna]) is a complex form of mirage visible in a narrow band right above the horizon. The term Fata Morgana is the Italian translation of Morgan le Fay of Arthurian legend. These mirages are often seen in the Italian Strait of Messina, and were described as fairy castles in the air or false land conjured by her magic.
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 at sea or on land, 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 upright images 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 bend when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed.[1] 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.
Observing a Fata Morgana<br>[edit]
Schematic diagram explaining the Fata Morgana mirage<br>A Fata Morgana is commonly seen in polar regions, where it may be known as an iceblink, especially over large sheets of ice that have a uniform low temperature. It may, however, be observed in almost any area. In polar regions the Fata Morgana phenomenon is observed on relatively hot days. In Antarctica, over oceans, and over lakes, a Fata Morgana may be observed on cold days or can be seen in mist and fog.
To generate the Fata Morgana phenomenon, the thermal inversion has to be strong enough that the curvature of the light rays within the inversion layer is stronger than the curvature of the Earth.[1] Under these conditions, the rays bend and create arcs. An observer needs to be within or below an atmospheric duct in order to be able to see a Fata Morgana.[2] Fata Morgana may be observed from any altitude within the Earth's atmosphere, from sea level up to mountaintops, and even including the view from airplanes.[3][4]
A sequence of a Fata Morgana of the Farallon Islands as seen from San Francisco<br>The above sequence as an animation<br>A Fata Morgana may be described as a very complex superior mirage with more than three distorted erect and inverted images.[1] Because of the constantly changing conditions of the atmosphere, a Fata Morgana may change in various ways within just a few seconds of time, including changing to become a straightforward superior mirage. The sequential image here shows sixteen photographic frames of a mirage of the Farallon Islands as seen from San Francisco; the images were all taken on the same day. In the first fourteen frames, elements of the Fata Morgana mirage display alternations of compressed and stretched zones.[1] The last two frames were photographed a few hours later, around sunset time. At that point in time, the air was cooler while the ocean was probably a little bit warmer, which caused the thermal inversion to be not as extreme as it was few hours before. A mirage was still present at that point, but it was not so complex as a few hours before sunset: the mirage was no longer a Fata Morgana, but instead had become a simple superior mirage.
Fata Morgana mirages are visible to the naked eye, but in order to be able to see the detail within them, it is best to view them through binoculars, a telescope, or as is the case in the images here, through a telephoto lens. Gabriel Gruber (1740–1805) and Tobias Gruber [sl] (1744–1806), who observed Fata Morgana above Lake...