The Highway Mirage

Inferior Mirage Formation (Diagram courtesy, Spectrum Educational Enterprises)

As shown in the accompanying diagram, a layer of hot air near the ground has refracted the light from the sky upward with a broad, nearly U-shaped bend. We see a mirage "water" illusion because our mind initially interprets the light rays reaching our eyes as having come along a straight path originating from the ground. Thus, the image of that patch of sky and cloud we see "on the ground" is interpreted as a surface "pool of water."

One of the more interesting visions that may appear in an inferior mirage is the illusion of someone walking on water. A person strolling along the shoreline, or on a sandspit extending outward from the shore, of a hot sandy beach on which an inferior mirage forms may easily appear to be walking on the water's surface.

Inferior mirages can actually be seen anywhere a surface is considerably hotter than the air above it. They can form over the hot metal of an automobile or truck, artificial turf, and building roofs. The source of the heat need not be the sun, for a hot engine or barbeque can raise the temperature of its metal hood enough to form conditions for seeing an inferior mirage. They may even form over heated vertical surfaces such as a rock face or wall, giving a surreal scene such as a "pool of water" clinging to a vertical surface.

Next time you are out for a drive or a walk and see that "pool of water" in the distance, look more closely. Blue sky often mixes with cloud in an inferior mirage vision. Look closely and you can often see details in the mirage such as oncoming vehicles or trees, details in a mirage you have never seen before.

Copyright 2001, Keith C. Heidorn, All Rights Reserved. (Illustration courtesy of Spectrum Educational Enteprises, ©1999.)

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