An optical effect, sometimes seen on the ocean, but more
frequently in deserts, due to total reflection of light at the surface
common to two strata of air differently heated. The reflected image is
seen, commonly in an inverted position, while the real object may or
may not be in sight. When the surface is horizontal, and below the eye,
the appearance is that of a sheet of water in which the object is seen
reflected; when the reflecting surface is above the eye, the image is
seen projected against the sky. The fata Morgana and looming are
species of mirage.