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Mirages are rearranged reality

Posted in Oddities, Puzzle, Science on Thursday, 9 June 2011

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This edited article about mirages originally appeared in Look and Learn issue number 962 published on 16 August 1980.

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A Mirage

A person dying of thirst in the Gobi Desert may imagine many things in his delirium – but the mirage he sees is real enough.

Many people think that a mirage is nothing but an illusion. It is not. A mirage is an optical phenomenon that can be seen by the coolest observer and photographed. The elements going to make up the mirage – traditionally palm trees – are real: they are, however, rearranged according to the laws of refraction.

What happens is that light changes its direction of travel – it refracts – on its passage through an atmosphere having an unusual distribution of air density. An increase in density of the air decreases the velocity of light passing through it. The result is a displaced image.

It can easily be seen how these conditions could arise in desert regions. On calm, clear summer days the surface of the ground becomes strongly heated. A layer of hot air is formed, which reflects the sky so as to suggest a blue pool of water. It also reflects nearby objects. A mirage is produced – of, say, a palm tree reflected in a pool of water. The reflection and the pool may be illusory, but there has to be a palm tree there to begin with.

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