Final answer:
Mirages are formed by atmospheric refraction, where light rays bend as they pass through hot air near the ground. This creates an illusion of reflected light from distant objects, resembling a pool of water.
Step-by-step explanation:
Mirages are formed by the phenomenon of atmospheric refraction, which is the bending of light as it passes through air or water. In deserts, where there is a hot layer of air near the ground, the refractive index of air is lower for air at higher temperatures. This difference in refractive index causes light rays coming from the horizon to strike the hot air at large angles, resulting in mirages.
This refraction of light in the hot air creates an illusion that light from faraway objects is being reflected by a pool of water that is not actually there, giving rise to the common mirage effect observed in deserts.