This article is about mirage, an optical phenomenon. For other meanings, see Mirage (disambiguation).

A mirage is an optical phenomenon which often occurs naturally. The kind most commonly seen (known as inferior mirage, because the inverted image lies below the upright one) is produced by the refraction of light when it passes into a layer of warm air lying close to a heated ground surface. This is an example of gradient index optics.

In deserts, mirages may give the appearance of a lake or other large body of water in the distance; this is actually an image of the sky being refracted back up from the warm air lying over the sand. On tarmacked roads, mirages give the impression of puddles of water in the distance.

Example images of inferior mirages

A road mirage, a type of inferior mirage

Superior mirage

More spectacular mirages (superior mirages) are produced by a temperature inversion near eye level. In these, the inverted image lies above the upright one; and there may even be several alternating layers of upright and inverted images. These are known as the Fata Morgana.

Example images of Superior mirages
(Temperature inversions over cold Lake Superior)

Trees shown which are normally invisible below horizon, a superior mirage reflected from above

Sunrise first light caused by super-refracted sunlight

Double sun sunrise caused by a super-refracted sun