Fata Morgana (Mirage)

Fata Morgana or Mirage is an optical phenomenon. It arises due to uneven heating of the air above the ground, which is forming layers of air of different temperatures (and of varying refractive index). At the interface of these layers, a total reflection of light then may take place ‒ the air layer acts as a mirror. Fata Morgana is basically a superior mirage, but an inferior mirage also naturally occurs sometimes.

Superior mirage occurs in areas with huge thermal inversions. The light beam emerging from point A (the ship) proceeds through the atmosphere at an upward angle. Consequently, with the height the air density decreases, as well as the refractive index, causing that the angle of incidence may reach values ​​for total reflection at point O. The beam is then refracted back to the surface until it enters the observer's eye in the point P. From the point P then one can see image A' tangentially to the beam.

Inferior mirage occurs during very intense heating of the earth's surface by solar radiation. The light beam which emerges from the object A (automobile), passes through the super-heated boundary layer with an anomalous increase in air density into the indicated eye of the viewer P., In this case, the beam at point O reaches the angle for total reflection and the beam is refracted upwards. Observer P then in the direction of the tangent from his eye to a given beam sees a mirror image A'.