Can mirages occur in cold places? © Getty Images

Can mirages occur in cold places?

A desert mirage looks like a pool of water, but an arctic mirage will fool you into thinking land is nearby.

Asked by: Uzma Padia, Preston

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They sure can. Early Norse sagas refer to them as ‘hafgerdingars’ (meaning ‘sea hedges’), because they looked like land far out at sea. What they were seeing was an image of land that was far over the horizon. Such ‘arctic mirages’ (also known by the Icelandic word ‘hillingar’) form because the density of the air near the cold ground is higher than that of the air above, and light rays passing from the warmer to the colder air are ‘bent’.

They are different to desert mirages in that the light is bent in the opposite direction (because the air is warmer, and less dense, near the ground in the desert). Desert mirages are upside down, and lower than the original object, while hafgerdingars are the right way up, and higher than the original object. Desert mirages are often images of the blue sky, while arctic mirages are usually images of distant land. Intriguingly, it may have been such mirages that led the Norsemen to the discovery of Iceland and Greenland.

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