What causes the wavy light by fires?

Question

You've all seen it, you look at the space above a bonfire and the image behind it waves and wobbles, distorting the background. It shows up on cameras and stuff like that, too.

What causes that to happen? Just curious.

? · Accepted Answer

The fire heats the air. Hot air has a different index of refraction than cool air, meaning that it bends light at different angles. The light coming to your eye through the hot air is bent at a different angle than through the cold air, so the objects that you are seeing with that light look distorted in comparison. Furthermore, the shape of the hot air region above a fire is constantly changing due to the chaotic motion of the flame and the turbulent flow of the hot air, so that the refraction-induced distortion of distant images changes in the same way. The images sway all over the place ("wave", as you say), because the flame is swaying all over the place and the hot air is moving turbulently as it flows upward. This is the same reason you can see mirages on the surface of roads on hot days.

Ẩn danh · Answer

due to heat of fire air surround the fire become hot and flow upward. but all time hot air no stay at same temperature. 

now during this process the air density in our vision path changes continiously. (plz see a bar code to imagine this density). thats why object vibrate/flactuate.

star at n8 sky also vibrate for the same cause.

What causes the wavy light by fires?

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