Mirages
I’ve ran into a few people who
don’t actually believe that mirages exist. The only
experience they had with them was in cartoons, when the
person stuck in the desert would see a lush oasis ahead on
him, but it disappears before he can get close. As silly as
that does seem, it does a fairly accurate job of describing
mirages.
From: Wikimedia Foundation
Imagine you’re driving down the road with the sun bight and shining on a clear day. It’s midsummer and there is not much wind. What’s happening is the sun is heating up the road faster than the air it shines through, so the road is radiating heat back at the air above it. This causes the air directly above the pavement to be hotter than the above it. When gas heats up, it expands, so the warmer air next to the pavement has a lower refractive index than the air above it. This means that the light that shines down at an angle will slowly bend to be more parallel to the road until it hits the critical angle and reflects back upward. So when you see a reflective pool on the ground at a distance on the hot day, it is actually the reflection of the blue sky, and not water.