There Mirage in question is not a legend, but a complex form of mirage which manifests itself along the horizon line of the sea (but also of land) with respect to the observer and which can be observed in some specific areas of the world (it is common, for example, on the Strait of Messina). This curious optical phenomenon is named after Morgana the Fairy for a very specific reason: this Celtic mythological figure linked to King Arthur cast spells and enchantments, and tempted sailors by showing them fantastic castles suspended on the surface of the water, leading them to their death. During this phenomenon, distant objects (islands, coasts, boats, cities) appear so distorted that they are almost unrecognizable: continually evolving, they seem compressed, stretched upwards (like towers or obelisks). When the phenomenon occurs on the surface of the water, sometimes you can notice that some ships appear detached from the surface of the wateras if they were floating. The phenomenon occurs in conditions of thermal inversion (i.e. when the air at high altitude is warmer than the air at lower altitude) and is due to the fact that therefractive index of the air (i.e. its effectiveness in deflecting light rays) varies with altitude due to the differences in temperature between the various layers of air.
The optical explanation of the Fata Morgana
The Fata Morgana occurs when a layer of warm air is found above a layer of colder air, which is precisely the phenomenon of thermal inversion. Warm air has a lower refractive index than cold air, that is, it deviates the trajectories of light rays less. The light of a very distant and/or high object will therefore reach our eyes after having travelled a downward curved trajectorywhich makes us believe that the object is positioned higher than it actually is: this explains the phenomenon of ships appearing to float in the air on the horizon!
This effect is especially noticeable at sea, where the horizon is far and flat and thermal inversions are not uncommon. For the phenomenon to occur the weather must be serene and there must be no particular air turbulence.
Where you are most likely to see the Fata Morgana
It is not uncommon to observe this refractive effect in polar regionsespecially on large ice fields, when it is cold. In deserts and along the marine horizonson the other hand, it is the opposite: there the Fata Morgana shows itself when the temperature is higher than average. In both cases, however, it is essential that a thermal inversion occurs strong enough to bend the light rays.
In Italy the phenomenon can be observed on Strait of Messina just at this time of year: when it is particularly hot in the morning, in fact, From the Calabrian coast you can see the city of Messina under the effect of Morgana. This is because on the surface of the sea of the strait small droplets of rarefied water act as a magnifying glass. The impression is that not only is the city closer, but that the images fade, blurring into turrets.
The phenomenon has been observed several times also in the countryside near Alberesein the Maremma Grossetana. Here, the fields cultivated with wheat or sunflowers are illuminated by the sun, and in some particular conditions of clear sky, looking at these yellow horizons you can see the Fata Morgana.
