Question

how does an mirage form?

Answer 1

Mirages are optical illusions created by special atmospheric conditions. They occur when light rays are bent or refracted when they pass through adjacent layers of air of different temperatures or densities. Under certain conditions, such as over a stretch of pavement or desert air heated by intense sunshine, the air rapidly cools with elevation and therefore increases in density and refractive power. 

A mirage may occur when a person is driving and sees what seems to be a pool of water lying on a hot paved road ahead.But when the person reaches the spot,the water had disappeared or has seemingly moved further on the road.
It is bcz of the denser air below as light passes through from the less dense air to the dense air,refraction takes place and a mirage is formed.

Hope this helps :)

Answer 2

Mirages are like the optical illusions formed due to the total internal reflection. This happens when a light beem bends. For example, we see mirages like water ponds in a hot day in the desert. When light travel through the atmosphere from cooler to warmer it bends due to the change in speed of the light in the space and of the earth. This is what happens!! This is why we see these mirages like water in the roads when the light touches the hot air closer to the ground. Hope this helps!!