We've all seen the scene in the movie where the thirsty desert traveler has been trekking for hours. Then he notices a large body of water on the horizon. He races towards the sea, which becomes closer and closer until he leaps into the air, only to land in the sand with no water in sight. This is a well-known example of a mirage which is an illusion that you think something is there but not actually there.
Mirage is an optical illusion induced by climatic circumstances, particularly the impression of a sheet of water in a desert or on a scorching road generated by heated air refracting light from the sky are common phenomena of mirage that people face.
Mechanism of Mirage
Mirage occurs by the temperature difference between the ground and air and It happens when the ground temperature is high and the air temperature is low. Light waves from the sun normally go straight through the atmosphere to your eye. However, light moves at different speeds in hot and cold air. When light passes through the cold air and into the hot air layer, it is refracted (bent). The light from the sky is refracted nearly into a U-shaped bend by a layer of very warm air near the ground.
Image from: https://cdn.britannica.com/31/63031-050-EA430436/rays-path-image-line-conditions-layer-observer.jpg
Our brains deceive us by supposing that refracted light follows a straight path. As a result, we trace the light back to its source, which looks to be the ground. When all of this is taken into account, refracted light from the sky is regarded as straight, allowing us to see an image of the sky on the ground.
Mirages in our life
Mirage is not a rare phenomenon that is difficult to find. It is very possible that the mirage can happen in our daily life.
When you drive on the road during the middle of the summer day, it sometimes looks like a pool of water is on the road. However, if you actually observe the road closely, there is no water because of the refraction of light. The air on the road surface is heated hot by intense sunlight, and the air above the road becomes colder than the road surface. As shown in the figure below, light reflected downward from the sky usually passes through the cold air and goes straight toward the road. At this time, the light is refracted upward by hot air as it passes close to the road, and in the eyes of the observer, it looks as if light has come from the hot road. Some of the light reflected downward from the sky is directly visible to the observer without refraction, so you can see the actual sky. Therefore, one of the images of the sky is the actual image of the sky, and the other is the mirage of the sky seen upside down. The sky became the object of a mirage, making it look like water is stuck in the road.
Image from: https://www.scu.edu/media/portals/illuminate/blog/PhilKesten6-warmer-cooler-air-illistration.png
Its concept also applies to the desert. The surface of the desert is heated by the sunlight which eventually becomes an atmosphere where the surface is hotter than the air of the desert. The light refracts when it passes through the cold air and into the hot air which eventually becomes a mirage of Oasis. People would be deceived by this mirage and thinks as an oasis while it is just a reflection of the sky.
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