Mirage

Mirages are divided into lower, visible under the object, upper, visible above the object, and side.

Lower Mirage

It is observed with a large vertical temperature gradient (its fall with height) over an overheated flat surface, often a desert or asphalt road. An imaginary image of the sky creates the illusion of water on the surface. So, on a road that goes into the distance on a hot summer day, a puddle is seen.

Upper Mirage

Observed over a cold earth's surface with an inverse temperature distribution (air temperature rises with increasing altitude).

Upper mirages are generally less common than lower ones, but more often they are more stable, because cold air has no tendency to move up, and warm air - down .

Upper mirages are most common in the polar regions, especially on large, even ice floes with stable low temperatures. Such conditions may occur over Greenland and in the Iceland region. Perhaps due to this effect, called hillingar (from the Icelandic hillingar ), the first settlers of Iceland learned about the existence of Greenland ^[1] .

Upper mirages are also observed in more moderate latitudes, although in these cases, they are weaker, less clear and stable. The upper mirage can be straight or inverted, depending on the distance to the true object and the temperature gradient. Often the image looks like a fragmentary mosaic of straight and inverted parts.

Upper mirages can have a striking effect due to the curvature of the Earth. If the bending of the rays is approximately the same as the curvature of the Earth, the rays of light can travel long distances, as a result of which the observer sees objects far beyond the horizon. This was observed and documented for the first time in 1596, when a ship under the command of Willem Barents, in search of the Northeast Passage, got stuck in the ice on Novaya Zemlya . The crew was forced to wait for the polar night . In this case, the sunrise after the polar night was observed two weeks earlier than expected. In the 20th century, this phenomenon was explained, and was called the “ New Earth Effect ”.

In the same way, ships that are actually so far away that they should not be visible above the horizon can appear on the horizon, and even above the horizon, like upper mirages. This may explain some stories about flights of ships or coastal cities in the sky, as described by some polar explorers ^[2] .

Side Mirage

Side mirages can occur as a reflection from a heated sheer wall. The case is described when the even concrete wall of the fortress suddenly shone like a mirror, reflecting the surrounding objects. On a hot day, a mirage was observed whenever the wall was sufficiently heated by the sun's rays ^[3] .

Fata Morgana

Complex phenomena of a mirage with a sharp distortion of the appearance of objects are called Fata Morgana . Fata Morgana (Italian: fata Morgana - Morgan fairy, according to legend, living on the seabed and deceiving travelers with ghostly visions) is a rare complex optical phenomenon in the atmosphere consisting of several forms of mirages in which distant objects are visible multiple times and with various distortions .

Fata morgana arises in those cases when several alternating layers of air of different density are formed (usually due to temperature differences) that can give mirror reflections. As a result of reflection, as well as the refraction of rays, real-life objects produce several distorted images on the horizon or above it, partially overlapping each other and rapidly changing in time, which creates a bizarre picture of a veil-morgan.

Volumetric Mirage

In the mountains it is very rare, under certain conditions, you can see a “distorted self” at a fairly close distance. This phenomenon is explained by the presence of “standing” water vapor in the air.

Phantom Far Vision

One striking example of such phantoms is the “ Flying Dutchman ”. According to maritime myths, the captain of a ghost ship is forever condemned to roam the open sea, not mooring anywhere. The sailors never expected anything good from a meeting with a mystical ship - it always signified misfortune and shipwreck.

Almost all stories about him sounded about the same - a ghost ship sailed right at them, did not respond to signals and screams, and then suddenly disappeared into the fog. In fact, the crew of the ship saw in front of them the projection of the ships that were at that time at a great distance from them.

A long-range mirage appears when the earth's surface heats the air masses, after which they go up and cool. If for some reason a warmer one appears above the layer of cold air masses (for example, winds from the south brought it here) and at the same time a very thin layer, and the temperature difference between them turns out to be quite large, then refraction will occur. Light rays that are reflected from objects that are located on the earth's surface will make an arc and go back down, but not to their immediate source. They find themselves in dozens, and sometimes hundreds of kilometers from it.

• Astronomical refraction

• Mirage // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
• ATMOSPHERIC PHENOMENA - CLASSIFICATION AND DESCRIPTION // meteocenter.net.
• Article about mirages in the magazine "Around the World"