Mirage

A mirage is an optical phenomenon in which a distant object appears to be present, even though it is not actually there. The refraction of light rays causes this optical illusion as they pass through layers of air with varying densities, resulting in a deceptive appearance. For instance, in certain conditions, when the air rapidly cools with an elevation over an extent of desert air or pavement heated by extreme sunshine, it increases in density and refractive power. When sunlight reflects downward from the upper portion of an object, such as the top of an object in the desert, it enters the cool air in the normal way but then curves upward after entering the rarefied hot air near the ground. This makes it appear to the viewer’s eye as though it is generated below the heated surface, creating a direct image of the object, as well as its upside-down reflection in the water. The double image is sometimes mistaken for a lake or sheet of water when the sky is the object of the mirage.

In certain cases, a cool and dense layer of air can be found beneath a heated layer, particularly over a body of water. In such situations, the opposite of a mirage occurs, known as “looming”. This phenomenon occurs when light rays reach the eye from below the line of sight, causing an object that would ordinarily be out of view, such as a boat located below the horizon, to appear to be lifted into the sky. Unlike a typical hallucination, mirages are genuine optical effects that a camera can photograph since light beams are actually refracted to produce a false image at the viewer’s position.

Formation of Mirage

Mirages are caused by atmospheric refraction and are predominantly observed in settings where there are drastic variations in the atmospheric temperature, such as over cold water bodies or deserts (mirage meaning). The refraction which happens close to the Earth’s surface is fundamentally due to temperature gradients where the beams of light will be deflected toward the cooler section of the interface.

The bending of light rays through refraction causes them to travel upwards from a heated surface, thus distorting the image and creating a mirage that resembles a wet surface. This type of mirage is commonly referred to as a “puddle mirage”. In addition, when light from vehicles ahead moves towards a hot surface, it is refracted back upward, resulting in mirage images below the vehicles.

What Is Meant by an Inferior Mirage?

An inferior mirage occurs when the mirage image appears below the actual object. The light rays emanating from a particular distant object move through almost the same layers of air and are all refracted at approximately the same angle. Consequently, the rays coming from the object’s top will arrive at a lower point than those originating from the bottom. Typically, the image is inverted, heightening the illusion that the sky image observed in the distance is a reflective surface on a pool of water or oil that acts as a mirror.

While the aerodynamics are active, the image of an inferior mirage remains steady compared to the Fata Morgana (a Fata Morgana is a mirage that creates the illusion of objects floating above the horizon, caused by light refraction through layers of air with different temperatures and densities), which can alter within seconds. Due to the warmer air rising and the denser cooler air sinking, the layers combine, leading to turbulence. Consequently, the image gets distorted, and it may shake or be vertically extended (towering) or compressed (stooping). In certain instances, a combination of vibration and extension may occur. If there are multiple temperature layers present, the mirages may blend, leading to double images. In any case, mirages are usually not more significant than approximately half a degree tall, about the angular width of the Sun and Moon, and originate from objects situated between dozens of metres and a few kilometres away.

What Is Meant by a Superior Mirage?

In a superior mirage, the mirage image seems to be positioned above the actual object. This type of mirage arises when the air beneath the line of sight is colder than the air above it. This unique setup is referred to as a temperature inversion, where warm air above cold air opposes the typical temperature gradient of the atmosphere during the day. As the light rays pass through the temperature inversion, they bend downwards, resulting in the image appearing higher than the actual object, hence the term “superior”.

Superior mirages are frequent in polar areas, particularly over expansive ice sheets with a uniform low temperature. In more temperate latitudes, they also occur, but they are less strong and less smooth and stable. For instance, a far-off coastline may appear lower and then higher (and, therefore, closer) than it genuinely is. The turbulence creates dancing spikes and towers, leading to what is known as the Fata Morgana or hafgerðingar in Icelandic. Depending on the temperature gradient and the distance of the actual object, a superior mirage may appear right-side up or upside-down. The image often appears as a distorted combination of upward and downward sections.

What Is Heat Haze?

Heat haze or heat shimmer is a phenomenon that occurs when an object is viewed through a layer of heated air. This is usually experienced when looking through the exhaust gases emitted by aeroplane engines or observing an object over hot asphalt. When the sun heats a road, the air closest to the surface becomes hotter than the air above it, causing a difference in temperature between the denser cooler air and the hot air at the road’s surface. This contrast produces the blurred, shimmering effect that is visible. When light travels from hot to cold air, it changes direction, resulting in the same optical illusion that occurs when a pencil is put in a cup of water.

When the angle of the light from the sky is shallow in relation to the road, it is refracted by the index gradient, creating an illusion of the sky being reflected on the road’s surface. This can take the form of a liquid pool (often water, but also possibly other liquids, such as oil) on the road, as some types of liquid can also reflect the sky. As the observer approaches the miraged object, the illusion appears to move into the distance, creating the same effect as approaching a rainbow.

What Is Fata Morgana?

A Fata Morgana is a type of superior mirage that appears as a complex and distorted image located in a narrow band just above the horizon. The objects on which the mirage is based are significantly altered, often to the point of being unrecognisable. These mirages can occur on land or at sea, in polar regions or deserts, and can involve a wide range of distant objects, such as boats, islands and coastlines. Fata Morgana mirages are often rapidly changing and consist of multiple inverted (upside-down) and erect (right-side-up) images stacked on top of one another. They also exhibit compressed and stretched zones that alternate.

The bending of light rays passing through air layers of varying temperatures creates an optical phenomenon known as a Fata Morgana, which is visible when a steep thermal inversion forms an atmospheric duct. In still weather, a layer of warmer air may rest over colder, denser air, creating an atmospheric duct that refracts light and produces a sequence of inverted and erect images. However, the presence of a duct is necessary for a Fata Morgana, and thermal inversion alone is insufficient. Although thermal inversion often occurs without the formation of an atmospheric duct, the latter cannot exist without the former.

A Fata Morgana is most frequently observed in polar regions, particularly over expansive ice sheets that have a consistently low temperature. However, it is not limited to these regions and can be seen in many different areas. In polar regions, the Fata Morgana phenomenon is typically seen on relatively cold days. In contrast, it may be observed on hot days over lakes, deserts and oceans.

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