In a desert a mirage is caused when air near the ground is hotter than air higher up. As light from the sun passes from cooler to warmer air it speeds up and is refracted upward, creating the image of water. Mirages are also found at the poles. A warmer layer of air over a cold layer bends light rays so that images appear. From a distance, ships can appear to be floating several feet (metres) above the water. At the end of the winter, after the long absence of the sun, a reflection of the sun appears in a mirage days before it actually rises.
The rays that produce mirages are optical phenomenons but are real and can be photographed.
Photo: Mirage of iceberg. See more interesting atmospheric effects.