system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is that puddle mirage I see off in the distance usually on roads?
gpt
As you say, it's a mirage.

When it's very hot, the ground gets heated by the sun. The ground then heats the layer of air closest to it, by conduction. Given time, the hot air will rise - but initially, the air near the ground is hotter.

Light from the sky, as it travels to your eyes, has to travel through the highest layers of air first. It then moves into the lower, hotter layers of air. As it crosses this boundary, it changes speed - and when a wave changes speed, refraction will occur, which means that the light wave will change direction - or bend. So when the light from the sky reaches your eyes, the direction it's coming from is not from the sky, because its course has been bent.

Your brain sees the light from the sky, and it appears to be coming from the ground in the distance. The only explanation your brain can find for this is that there is a puddle in the distance, and that you are seeing the sky reflected in the puddle.