Have you ever watched a movie starring a helpless and thirsty explorer looking for water in a ruthless desert? Suddenly the explorer sees a big oasis full of luscious water. The explorer runs towards the oasis to find empty dunes and a sea of sand. Thinking his mind is playing tricks on him he continues his search for a drop of water. Well, I bet you have seen or heard a scenario close to this one. Most think that the oasis in the picture might just be a movie effect, but it can happen in real life! This hallucination is known as a Mirage. What is a Mirage and What Causes a Mirage? Maybe the Science Behind Mirage will assist our explorer and give him a reasonable explanation for that mysterious oasis.
What is a Mirage?
Before we look at what causes a mirage, we must understand What is a mirage. A mirage is an illusion that is caused by Earth’s atmosphere. Unlike in the movies, a mirage in real life looks like a sheet of water covering the ground. Mirages generally take place in hot environments. Like the unmerciful desert, our explorer is currently trapped in. We might also see mirages in scorching highways.
What Causes a Mirage?
Before diving deep into What causes a mirage we need a little revision about light and its properties. Light travels in a straight line when the air temperature is the same (hot or cold). A mirage takes place in a hot environment like a desert because there is a mix of cold and hot air here. If both temperatures, air is present, this will set up the perfect conditions for a mirage to appear. In the desert closer to the ground the air is hot and farther from the ground the air is cool. When these conditions exist, the light will take a curved path through the cold air. Light waves curve because the cold air “has a higher index of refraction than the warm air does.” as stated by Scientific American. At this point, the light photons travel faster through the hot air than the cold air is because the hot air is less dense. Research studies have found light photons are in a hurry and will only go from one destination to the other in the smallest amount of time. The light photons curve through the cold air because they believe that is the shortest route, even though they are covering more distance by making that curve.
Mirages show the raw result of the impatient photons taking the quickest path. When the perfect conditions exist then the mirage is made possible. The photons will take a curved path, but the viewer suspects that the photons proceed in a straight line. This is because the human brain is not capable to see the light photons' curve. This is what happens when our explorer is looking far into the desert. Meanwhile, as the light photons are taking a curved path, our explorer will not be able to interpret that the photons are taking a curved path and unfortunately sees in a straight line. Ideally, the explorer's brain comprehends that there is a water source or a pond because the color of the blue sky gets reflected. Unluckily, for our explorer vertical temperature gradient does reflect the sky as well. Our explorer mistakes the reflection of the sky for water.
To sum it up a mirage is an image of the clear blue sky. The light from the sky was refracted by the hot air. Since hot air refracts light differently than cold air. As a result, the photons aim to curve or bent towards the hot air to reach their destination faster. Since we never saw the curve, it is assumed that the light rays seen are straight but ultimately lead us to the reflected image of the sky. The vertical temperature gradient reflects the blue sky copying a property of water which leaves the poor explorer baffled.
DIY Mirage Experiment
Since mirages are caused by refraction, we will do a DIY experiment about them. To do the experiment you will need:
Water
Paper
Pen/Pencil
Clear Glass
Step 1: Draw two arrows facing the same direction
Step 2: Fill the clear glass with water
Step 3: Slide your paper around the glass.
You will observe that when you look through the glass, the arrows are facing the opposite direction. This is when the light waves get refracted. Refraction also plays a major role in the creation of mirages.
Our explorer should find some real water soon. Though the desert is an unwelcoming place for our explorer, I am sure he will find a way out. Though mirages might fool us occasionally there is interesting physics behind this natural phenomenon. Next time you spot a mirage on a hot summer day, connect to behind the scenes of the movie mirage. Our explorer may pick a more welcoming vacation spot for his next adventure. Thanks to my friend Kanushi for suggesting me the topic of mirage. Until next time! Sayonara!
Enjoy the journey, because the destination is a mirage ~Steven Furtick