What causes a mirage?

A mirage occurs due to reflection.U can c mirages in deserts or even on roads in summer.This is because the layers of air nearer to ground are hotter than upper layers hence a reflection occurs and the sky is seen as a reflectionn

A mirage is a naturally-occurring optical phenomenon, in which light rays are bent to produce a displaced image of distant objects or the sky. The word comes from the Latin mirare, meaning 'to appear, to seem'. This is the same root as for mirror. Like a mirror, a mirage shows images of things which are elsewhere. The principal physical cause of a mirage, however, is refraction and not reflection. A mirage is not an optical illusion. It is a real phenomenon, and one can take photographs of it. The interpretation of the image, however, is up to the fantasy of the human mind.

the mirage forms when the light rays passing through a relatively warm layer of air are bent upward from their path (ie. it is refracted)which depends upon the density difference between the two media. in the lower atmosphere the air density's greatest variations are caused due to temperature change. these mirages thus are commonly formed when the layer of air closer to earth becomes warmer incomparison to above layer-the relatively warmer the air, the greater the effect. these are called as inferior mirage. whereas superior mirage is formed when air is colder at the surface than above it or just go to the following link where mirage formation has been explained ; www.hk-phy.org

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