system
Given the following post, respond as if you're commenting on Reddit:
human
Why does the road reflect when it is hot out?
gpt
Asphalt is dark, so it absorbs sunlight and re-radiates it as heat. This warms up the air immediately above the road, so that air is warmer than the air above it. The boundary layer between the two layers of air (which are different densities because of their different temperatures) *refracts*, which is another word for *bends*, rays of light that approach the boundary layer at shallow angles (angles that are mostly horizontal, such as rays of light from an object much further down the road). This is the source of many optical illusions, or *mirages*.