Mirages are tricks of the atmosphere, optical illusions caused when a layer of air next to the ground becomes superheated from heat stored in the soil or in dark pavement. Depending on the altitude and extent of the layer, or layers, many kinds of mirages are produced. Water mirages paint lakes across parched desert sands, deluding desert travelers. Like puddles stretching across dry highway pavement, these mirages are produced when the boundary between superheated and normal air reflects the sky, looking like water on the ground. Mesas seem to float free, separated from the land by a layer of blue sky.
Mountain ranges clone themselves, growing upside-down mirror images attached at the peaks.
Several inverted pairs of images, one above the other, are called multiple mirages. One especially deceptive mirage is the Novaya Zemlya effect, named for the location in Arctic Russia where it was first seen. In the dark days of the northern winter, the sun appears to rise over the horizon weeks before it is due to return. The sun is actually below the horizon, but its image is reflected back and forth between the upper and lower boundaries of the atmospheric layer and projected above the horizon. The clear images of the city of San Diego seen at Yuma were telescopic mirages, sharp, stable and magnified images reflected at least several hundred miles away from the source image.