Fata Morgana. Originally the name of the legendary King Arthur’s sorcerous stepsister and Sir Lancelot’s spurned mistress, a fairy who was particularly fond of demonstrating her power by means of mirages. The more precise world of science defines a Fata Morgana as an atmospheric mirage that occurs when layers of air of different temperatures – and, thus, different density and refractivity – are juxtaposed or superimposed in such a way that the rays of light passing through them are refracted, change direction, and follow a zigzag course. It is also rumoured in confidence that Fata Morganas are cities inhabited by those who have died of thirst in the desert. There is a certain logic in this theory, given that a desert lacks any buildings which the dead could inhabit and haunt. It is only natural, therefore, that they should make their home in wandering mirages.
It is quite impossible to trap a Fata Morgana because it always retreats at exactly the same speed as the person or persons approaching it advance. To cite the so-called Nightingalian Unapproachability Equation governing mobile mirages: A [distance] = X [person approaching] ÷ S [speed] x T2 [time squared]. In other words, the distance between oneself and a Fata Morgana remains constant however quickly or slowly one approaches it.