Fata Morgana

A mild version of one anyway, visible this morning from the living room window. Caused by a temperature inversion. 'Normally' air gets colder the higher you go but with a temperature inversion there is a 'lid' of warm air above a layer of colder air. Light moving out from an object inside the cold layer is refracted when it enters the warmer air. As the warmer air is less dense, this refraction bends the light downwards and if the temperature difference, and therefore the air density difference, is big enough this bending will be greater than the curvature of the earth, letting us see something that is physically over the horizon. Our brains assume that light only travels in straight lines and therefore the object appears to be floating. Known as a Fata Morgana after the Italian for Morgan le Fey in the Arthuruan legends.