Mirage

From The Book of THoTH (Leaves of Wisdom)

A mirage, derived from the Latin mirari, meaning 'to be astonished', 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 (see highway mirage). 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 tarmac roads, mirages give the impression that distant objects are being reflected by a puddle of water on the road.

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.

Abnormally large refraction of sunlight during sunrise or sunset can produce sunrises much earlier than predicted or sunsets much later than predicted. The conditions necessary for such refraction occurs most often, but not exclusively, in polar regions where strong surface temperature inversions can be geographically extensive and homogeneous. This mirage is often called a Novaya Zemlya mirage.