The top of a small island on the horizon is "mirrored" in the sky above, creating the illusion of a disc-like object that hovers in mid-air.

[Still taken from Les mirages, Histoires de chimères et de la fée Morgane, a documentary film by Michael ENGLER, broadcast by Arte on April 18, 1998. Copies of this remarkable film can be purchased at : http://www.zdf-enterprises.de.]