Breakdown: Why do we see highway mirages?
MEMPHIS, Tenn. (WMC) - Ever been on driving in the car and you see what looks like water on the road up ahead? But as you get closer the “water” disappears?
That’s a mirage.
People sometimes label a mirage as an illusion or as a hallucination. But, a mirage is neither one of those. Illusions and hallucinations are products of the mind. Mirages, however, are a result of the physics of Earth’s atmosphere.
You know how a pencil or utensil in a glass of water can appear broken or bent? Our atmosphere can cause some distant images to undergo a similar effect.
Atmospheric refraction is the result of light deviating from a straight line. It usually happens as light passes through the atmosphere at times when our planet’s air may be more or less dense, depending on its height above the ground.
On a hot, sunny day, the sun heats the road, and because roads are generally black, they absorb a lot of heat and become hotter than light-colored objects. This increases the air temperature just above the surface of the road.
This creates an uneven medium, as the air just above the road becomes somewhat less dense than the rest of the air.
Now the sun’s rays pass through the air in a straight line, but when they reach the relatively warmer and less dense layer just above the road, their speed increases slightly, and they change course, being refracted to reach the eyes of the observer.
In other words, a highway mirage is an inferior mirage, caused by the fact that the road is hotter than the air above.
What’s being refracted, exactly, to cause the appearance of water? It’s actually the reflection of the sky... The highway mirage is due to refracted light from the blue sky just above your horizon.
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