Mirages: A Real Image, or a Trick of Nature?
Mirages are a staple of desert adventure stories. Weary travels, who have gone days without food or water, think they see a vast expanse of water in the middle of the desert, and eagerly run towards it, only to find nothing but the same miles of sand. What causes this? Are they going mad, or is the earth playing some kind of cruel trick on them?
What Is A Mirage?
Mirages aren’t just in stories, though. They exist in the real world. Have you ever “seen” water on the road while driving? You may know it’s a mirage, but still wonder what causes it.
A mirage occurs when the air at one level is hotter than the air at an adjoining level. This creates a rapid shift in air density. When light passes between the different levels, the shift in density causes the light to bend, creating a mirage. This occurs, for example, on a hot summer day when the asphalt road has been under the glow of the sun all day.
Types of Mirages
There are two main types of mirages: superior and inferior.
- Inferior mirages occur when the mirage is located underneath the real object. Usually, this makes the mirage appear upside down. While they are seen on roads, inferior mirages are also likely to occur over lakes, oceans, or other bodies of water. When someone sees an inferior mirage, the image they see is usually bright and blueish. Heat haze is a type of inferior mirage. This occurs when an object is viewed through a layer of heated air, causing it to appear hazy.
- A superior mirage occurs when the air below the line of sight is colder than the air above it — this is also called a temperature inversion. This phenomenon causes the light rays to bend down, making the image appear above the real object. Superior mirages are less common than inferior mirages.
The rarest type of mirage is a Fata Morgana. A type of superior mirage, a Fata Morgana is a rapidly changing mirage. It occurs when rays of light bend as they pass through layers of air at different temperatures. To produce a Fata Morgana, the thermal inversion must cause the curvature of the light rays to be stronger than the curvature of the earth. When it occurs, it obscures the actual image of an object, and can affect many kinds of objects, including boats and coastlines. Fittingly, the name Fata Morgana comes from a powerful sorceress in Arthurian legend; these mirages are mystical and disorienting, often seeming like something straight of a magical story.
Science explains why mirages occur, but that doesn’t make them any less strange or fascinating. Next time you see water on the road, don’t be fooled by one of nature’s trickiest optical illusions!
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