Weather watch: Looking for the classic mirage

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mirage desert
The still air creates a mirage in the Kenyan desert, (digital composite). Photograph: Pete Turner/Getty Images

All of us are familiar with mirages. We have all seen a shimmering on the hot surface of a road that looks like water but is in fact the reflection of the sky. In the desert larger mirages can lead thirsty travellers to believe that they are approaching water.

These tricks of the light require special weather conditions: still air and layers of cooler or warmer air on top of each other to literally bend the light. What is not so generally known is that these effects also occur over water and sometimes project images over large distances.

It was therefore with considerable surprise that John D Heys of Guestling, near Hastings, looked towards France on 21 August and saw a group of buildings in the middle of the Channel. The French coast is 40 miles away, and while buildings and hills behind can be seen with binoculars on a clear day, these looked only a mile away. A small boat, in reality several miles out from the coast, was sailing through the middle of these buildings that were enormous by comparison.

What Mr Heys was seeing was a classic mirage; the light was being bent by the layers of air of different temperature over a cool sea. His house, 107 metres above sea level, was in a perfect position to catch the magnified image of the French coast. There was no flickering, and the mirage was clear enough for Mr Heys to draw us a good likeness of a nuclear power station near Boulogne.

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