system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What are mirages?
gpt
It's quite simple, the mirage is where light is refracted through air at different temperatures (Cold to Hot).

Cold air is denser than warm air, and the bigger the difference the greater the refractive index. As light passes down from cool to hot air, it gets refracted (bent) upwards towards the denser air and away from the ground. 

Your eyes will see distorted rays coming from the ground and you essentially see a refracted image of the sky.