Why does rising heat cast a shadow?

Answer 1

It refracts the light like a prism.

Answer 2

As others have said, the temperature of the air affects its density. It turns out that the density of air affects the speed which light passes through it. When light passes through regions where it has different speeds, it bends. You can think of this like when you drive down the street and accidentally let one of your wheels drift off the road and into the grass--you feel a sudden pull to one side. When light passes through the heated air above a hot surface light bends away from some areas and toward others, creating the pattern of ripple-like shadows.

Answer 3

Warm air is less dense than cooler "normal" air. As a hot surface such as tarmac warms the air, the air becomes less dense and rises. As the density of the warmed air is less than that of "normal" air, light bends as it passes from denser cooler air to the less dense warm air in the same way as light bends as it passes from air into water.

As the air is warmed unevenly on a such a surface (due to different moisture contents, density of materials at various spots) and as cooler air come down to replace the void left by the rising warm air, the rate at which light is bent from one part of the volume of rising warm air to another differs. This results in what is seen as "shadows" in rising heat, as where light is mostly bent away from a particular spot, a darker area is seen and vice versa.

Answer 4

Variations in the density of the air caused by thermal gradients and turbulence cause "heat monkeys".

I swear I knew a gal from Tennessee that called them that.

Answer 5

It's because of fluctuations in air density and therefore index of refraction that causes the dark and light formations you see.

Answer 6

the different densities of air cause refraction of the light