Mirage in the desert is one of the most well-known optical phenomena. Mysterious and eerie, confusing travelers, mirages have long captured the attention of both researchers and poets. Let’s try to understand what they are.
Mirage as a Natural Phenomenon
There are upper, lower, and lateral mirages. A lower mirage appears when the air temperature decreases with height. They are most commonly seen above the desert surface (or above sun-heated asphalt roads). Lower mirages are the “puddles” on roads and “ponds” in deserts, resembling oases that don’t actually exist. Sometimes these mirages are called “lake-like”: they look like a mirror-smooth lake situated on sand or another surface. Naturally, trying to approach such a lake is futile.
Upper mirages occur when the air temperature at altitude is higher than directly above the surface. Such mirages can be seen in polar regions. Many researchers believe that it was thanks to such a mirage that the first inhabitants of Iceland learned about the existence of Greenland, which is quite far away. Upper mirages are unique in that they can “project” over vast distances.
A lateral mirage occurs when light rays are reflected from layers of air formed near a hot surface. For example, there have been cases described where a concrete wall appeared to be water or began to reflect surrounding objects like a huge mirror. Lateral mirages are extremely rare.
Why Do Mirages Appear?
The physics of mirages is quite complex but entirely explainable from a scientific point of view. Distant parts of the sky can be projected onto sand due to the refraction of light between layers of air with different temperatures. This is why it might seem like a blue body of water has appeared in the desert: the “image” of the sky has been transferred to the ground. By the way, mirages can be photographed. They are not perceptual illusions but rather physical phenomena like rainbows or solar halos.
Mirages can appear not only in deserts: they occur wherever there’s a difference in temperature between different layers of air. However, they are much more common in hot places. Additionally, “cold” mirages have their peculiarity: they allow you to see objects beyond the horizon. Such a thing is impossible in deserts.
Interesting Facts About Mirages
If the air is saturated with vapor, mirages can be extremely frightening. They appear at very close distances to objects: a person might see their own (quite distorted) reflection just two steps away.
Naturally, such phenomena can greatly frighten people who have no understanding of physics. Some even believe that seeing their exact copy foretells imminent death. This phenomenon is usually observed in mountainous areas.
The most realistic mirages occur in the Erg Chebbi desert. People think they see an oasis nearby. Meanwhile, the distance to the “oasis” can be hundreds of kilometers. Seeking life-giving water, hundreds of travelers have lost their lives.
What is a Fata Morgana?
Many think that a Fata Morgana is another name for a mirage. However, this is not the case. A Fata Morgana is one of the varieties of a mirage: an optical phenomenon in which distant objects become visible multiple times and with some distortions.
A Fata Morgana arises when several layers of air with different temperatures and densities form. As a result, objects are reflected multiple times in these layers, and the images overlap each other, creating bizarre pictures.
Mirages in Legends
In Ancient Egypt, people believed that a mirage was the ghost of a long-disappeared object or phenomenon.
Interestingly, the legend of the Flying Dutchman, which emerged in the 17th century, is also associated with mirages. According to the legend, the Flying Dutchman is a ship that perished during a horrific storm along with its entire crew. Many sailors claimed to have seen the ghost ship: it seemed to appear on the horizon, as if floating above the water. The ship emerged from the fog, sailed past without giving distress signals, and mysteriously disappeared.
Naturally, such a mirage could only evoke terror. It was believed that encountering such a ghost foretold the imminent death of the ship’s crew. However, nowadays scientists know that the illusion of a “floating” ship in the air arises from the interaction of sunlight and the tiniest water splashes above the sea surface.
A mirage is just a visual illusion caused by the optical properties of the atmosphere. There’s no need to fear seeing a mirage: you’re lucky to witness such a unique phenomenon!