system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can "waves" of gasoline fumes emitting from the pump be seen in the shadow of the pump on the ground, but when looking directly at the pump in the car, these waves are not visible?

This was a hard question to word. But basically I was pumping gas into my car the other night. The fluorescent lights were on above me, and I looked down and noticed the shadow of the pump in my car on the ground. In the shadow I could see that there were obvious waves/ripples seemingly coming from the sides of the pump. When I looked back up at the actual pump in my car and looked closely, I couldn't see anything similar. I'm assuming they were fumes from the gasoline, but what I want to know is why was I able to see them in the shadow, but not the actual thing?
gpt
gasoline vapor has a slightly different density than air. as light passes through the vapor, it changes direction slightly as it passes through the areas of differing densities. we see this as the visible shimmer, and the shadow thereof. Heat shimmer and rainbows are caused by the same mechanism- light changing direction (refracting) at the interface between two materials of different density. 



Lighting and position will affect whether or not you see the effect, but it is still there.