What is "irisation"

n. (context meteorology English) a colouring seen in iridescent clouds and on the borders of lenticular clouds

In meteorology, irisation, a type of photometeor, is multiple mixed iridescent colors caused by sunlight being diffracted in clouds. The colors are often brilliant and mingled together, sometimes similar to mother-of-pearl. They sometimes appear as bands parallel to the edge of the clouds. Irisation is caused by very uniform water droplets diffracting light (Within 10 degrees from the Sun) and by first order interference effects (Beyond about 10 degrees from the Sun). It can extend up to 40 degrees from the Sun. Irisation is sometimes seen along the borders of lenticular clouds. Irisations are named after the Greek goddess Iris, goddess of rainbows and messenger of Zeus and Hera to the mortals below.

Image:Irisation_or_iridescence_in_super-cooled_cloud_-_NOAA.jpg|Irisation or iridescence in super-cooled cloud droplets in cirrocumulus clouds. Image:Iridescent Cirrus behind Stratocumulus over Warsaw, June 26, 2005.jpg|Irisation in cirrus (or maybe cirrocumulus) clouds behind Stratocumulus (bottom), in the afternoon over Warsaw, Poland.