9 Famous Mirages That Play Tricks on the Eyes

Mirages are nature's version of optical illusions. Variables like the path of light particles, the curvature of the Earth, and air temperature can create false images that the eye is convinced are real. Fata Morganas, which make land and ships appear like they are floating in the air above the sea, have been unnerving sailors for centuries while mirages involving oases have given false hope to many thirsty desert travelers.

Most mirages can be explained scientifically by the speed of movement of photons (particles of light). Photons move faster through less dense warm air than through cool air. This is why mirages are common in deserts, oceans, and other places with hot or extremely varied temperatures.

Here are nine different types of mirages and a look at how, why, and where they occur.

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Fata Morgana

For sailors, Fata Morgana, a type of superior mirage, can be terrifying. The illusion occurs above the horizon on oceans and seas, particularly in polar regions. It makes distant objects, such as another ship or the shoreline, appear to be floating in the sky. This is not only an ocean phenomenon; Fata Morganas can occur on lakes or deserts as well.

Named after sorceress Morgan le Fay in the legend of King Arthur, Fatas Morganas appear when the light is refracted (or "bent") by contrasting air temperatures. The air near the ocean’s surface is sometimes cooled by the water, so the temperature is warmer at higher altitudes. Light passes through hot air more easily, so it reaches the eyes of a far-off viewer after refracting above the cooler air. Expecting light to travel in a straight line, the viewer’s brain perceives that the far-off object is floating above the surface.

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Sundog

A sundog (sometimes written as sun dog) is an atmospheric phenomenon that causes bright spots to appear on either side—and often both sides—of the sun. The mirage is usually seen when the sun is rising or setting. Sundogs may also have a faint halo that seems to arc around the sun. No matter where in the world the lights are seen, they appear approximately 22 degrees away from the sun.

Caused by light passing through ice crystals, the meteorological name for a sundog is a parhelion. The ice is contained in high, thin cirrus clouds or, in colder climates, in lower clouds. It is refracted through the crystals and appears as completely separate light sources. A nocturnal version of the mirage, called a moondog, has also been documented.

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Desert Mirage

Inferior mirage in the desert of Mongolia with a herd of Bactrian camels moving together along the tan sand beneath a blue sky with white cloud cover — Caroline Pang / Getty Images

Like Fatas Morganas, desert mirages occur because light bends to move through warmer, less dense air. In the desert, refraction-caused illusions are known as inferior mirages because they occur below the horizon. This is why inferior desert mirages usually appear as water-like images on the ground.

In the desert, the air is at its hottest near the surface, and it cools as it rises. The light refracts downward, causing the eye to see sky-like (or water-like) colors below the horizon. A similar illusion is very common on hot highway pavement. The road often appears wet or covered with puddles in the distance on an especially sunny day. This is caused by the same phenomenon that creates fake desert oases.

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Brocken Spectre

The Brocken spectre, named after the highest peak in Germany’s Harz Mountains, was first observed by mountain climbers. They noted the visual phenomenon in which ghostly human-like figures appeared to be looking at them through the high-altitude haze. In reality, they were seeing their own shadow.

The spectre occurs when the sun is behind the observer. The light casts a shadow, not on the ground but on clouds or fog that occur most often at high altitudes. The sunlight that shines around the individual creates a halo-like glow. When the clouds move, the figure may appear to move as well. This phenomenon requires a bright light source shining at a low angle. It can also occur at ground level on foggy days with a strong artificial light, such as the high beams of a car’s headlights.

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Magnetic Hill

A magnetic hill (or gravity hill) is more of an artificial optical illusion than a light-based mirage. One of the most well-known magnetic hills is located in the Indian province of Ladakh. The Srinagar-Leh Highway has a stretch of road that appears to run up a hill. However, if you put your vehicle in neutral, you will actually continue to move forward instead of rolling backward (downhill).

This illusion has nothing to do with gravity or magnetism. Instead, it has to do with the landscapes surrounding the road. The adjacent hills are sloped in such a way that it appears that the road goes up an incline. However, if you were able to block out the surrounding visual cues, you would see that the road ahead is sloping downward. The illusion is especially pronounced in Ladakh, but there are many documented examples of gravity hills around the world.

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Light Pillars

Light pillars—a phenomenon characterized by unnatural beams that seem to shoot up into the sky or down to the ground—can be caused by both natural and artificial light. This occurs when light bounces off ice crystals in the air. Because ice is involved, light pillars caused by artificial light that happen close to the ground are commonly seen during winter in cold climates.

Light pillars can sometimes be caused by light from the sun (they are referred to as solar pillars). When this occurs, the ice crystals are usually in high clouds. The shape of the crystals that create a light pillar is important. The crystals are usually flat, and they fall more or less horizontally, making it easier for them to continuously catch the light.

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Water Sky

Water sky is a phenomenon in which the reflection of water in the distance creates unnaturally dark spots on low clouds. These dark areas are an indication of water in the distance. Early polar travelers used water sky as a navigational tool. It helped them choose their route while traveling away from ice-covered areas.

Another phenomenon iceblink creates an unnaturally bright underside on low clouds. The unusual brightness comes from the daytime light reflecting off ice below the cloud. Often, the ice field will be too far for the naked eye to see, but iceblink is also used by travelers in polar regions to predict the presence of ice.

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Green Flash

Green flashes are a meteorological event that occurs right before sunset or just after sunrise. The name “flash” is quite apt. The phenomenon, usually a green spot above the normal circular rim of the sun, rarely lasts for more than a few seconds. Though the image appears and disappears quickly, it does not cause a flash across the whole sky.

The cause of a green flash is light reacting with Earth’s atmosphere. Because of the short duration, the phenomenon is difficult to see. You can increase your chances of observing a green flash by finding a level horizon, such as on the ocean, and waiting for sunrise or sunset.

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Omega Sun

Omega suns have the appearance of their namesake Greek letter when they are just above the water at the horizon. The legs, or bottom, of the omega are created by warm water heating cooler air just above the surface. The omega shape can be quite pronounced if the water is calm.

Like other ocean horizon mirages, omega suns are caused by light refracting through warmer air (in this case, near the surface of the water). Because the water—especially in an ocean, sea, or large lake—has a more constant temperature than the air, omega suns are common in colder climates during the winter.