Sometimes a person wandering in a desert may be so thirsty and sun- parched that he begins to see things that aren’t there. This is a hallucination, and not a mirage, for mirages really exist, and can be seen by anyone in the area at the time they appear!
A mirage is a trick of nature. In a desert, there is a layer of very dense hot air above the ground. This layer of air bends light rays passing through it, distorting the images of distant objects.
Sometimes, a distant mountain may seem to float in the air; other times, a mirror image of the mountain may be reflected off the layer of dense air; and still other times, light rays bouncing off objects beyond the horizon are bounced back and forth in the layer of dense air, and then the objects seem to be much closer than they are.
That’s why people in the desert sometimes see lakes that turn out to be mirages, the reflection of water beyond the horizon or of the sky itself.
Mirages can be seen at sea and in the polar regions too!