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An inferior mirage occurs when the temperature of the air decreases abruptly with height and so a distant object appears to be displaced downwards; in a desert a patch of sky may appear like water. A superior mirage occurs when there is a sharp increase in the temperature of the air with height and an object is displaced upwards; it appears to be floating in air and may often be inverted.
The brockenspectre, named after the Brocken, a peak in the Harz mountains of Germany, is a strange sight, but familiar to mountain climbers. The shadow of the climbers is formed against a mist or clouds when the Sun is low in the sky. The great size of the shadow is due to its extent through a depth of several metres, rather than lying in one plane.
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