Road Puddles: Why Do Hot Roads Look Wet?

Light usually travels in a straight line, but it can bend when it moves through air of different temperatures. On a hot day, the black road heats up the air right above it. This hot, thin air causes light rays to speed up and curve upward toward your eyes instead of hitting the ground.

Because the light from the sky is being curved toward you from the direction of the road, your brain gets confused. Your brain is used to light traveling in straight lines, so it assumes the blue light you see on the ground is a puddle of water reflecting the sky.

This specific trick is called an 'inferior mirage' because the image appears below the actual object. If you look closely, you might even see 'cars' in the distance with their reflections underneath them, just like they would look if they were driving through an actual lake of water.