Mirage

Mirage, optical illusion in the atmosphere in which the refraction of light passing through air layers of different densities causes non-existent images to be seen. Distant objects may appear to be reflected in water, as light rays traveling initially toward the ground have been bent upward by layers of hot air close to the surface. In some mirages objects seem to float in the air. This commonly occurs over cold surfaces such as ice or a cold sea, where warmer air overlies cooler air and bends light rays downward.