Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

. The colors resemble those seen in

soap bubble A soap bubble (commonly referred to as simply a bubble) is an extremely thin soap film, film of soap or detergent and water enclosing air that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds b ...

s and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. They sometimes appear as bands parallel to the edge of the clouds. Iridescence is also seen in the much rarer polar stratospheric clouds, also called nacreous clouds. The colors are usually pastel, but can be very vivid or mingled together, sometimes similar to mother-of-pearl. When appearing near the Sun, the effect can be difficult to spot as it is drowned in the Sun's glare. This may be overcome by shielding the

sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...

with one's hand or hiding it behind a tree or building. Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water.

Etymology

Irisations are named after the Greek goddess Iris, goddess of rainbows and messenger of

Zeus Zeus (, ) is the chief deity of the List of Greek deities, Greek pantheon. He is a sky father, sky and thunder god in ancient Greek religion and Greek mythology, mythology, who rules as king of the gods on Mount Olympus. Zeus is the child ...

and

Hera In ancient Greek religion, Hera (; ; in Ionic Greek, Ionic and Homeric Greek) is the goddess of marriage, women, and family, and the protector of women during childbirth. In Greek mythology, she is queen of the twelve Olympians and Mount Oly ...

to the mortals below.

Mechanism

Iridescent clouds are a

diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...

phenomenon caused by small water droplets or small

ice crystals Ice crystals are solid water (known as ice) in crystal structure, symmetrical shapes including hexagonal crystal family, hexagonal columns, hexagonal plates, and dendrite (crystal), dendritic crystals. Ice crystals are responsible for various at ...

individually scattering light. Larger ice crystals do not produce iridescence, but can cause halos, a different phenomenon. 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. If parts of clouds contain small water droplets or ice crystals of similar size, their cumulative effect is seen as colors. The cloud must be optically thin, so that most rays encounter only a single droplet. Iridescence is therefore mostly seen at cloud edges or in semi- transparent clouds, while newly forming clouds produce the brightest and most colorful iridescence. When the particles in a thin cloud are very similar in size over a large extent, the iridescence takes on the structured form of a corona, a bright circular disk around the Sun or Moon surrounded by one or more colored rings.

Gallery

File:CircumHorizontalArc GQ 07312012 1938.jpg File:Viet Nam.jpg, Ho Chi Minh City, Viet Nam. May 12th, 2024 File:IridescentCloudArran.jpg File:Iridescent Cloud.JPG File:Cloud iridescence 3.jpg File:CloudOberGatlinburg.jpg File:Cloud iridescence at Kokkola, Finland.jpg File:IrisationCloudsPICT4884crop640x480.jpg, Irisation in clouds over Wellington NZ File:Cloud Iridescence and Crepuscular Rays.jpg, Vibrant cloud iridescence captured before sunset File:Iridescent cloud edge.jpg File:At Teide Observatory 2019 027.jpg, Iridescent clouds seen in Tenerife File:Cloud-iridescence-Parker-Canyon-AZ-Aug-6-2022.jpg, Parker Canyon, AZ. Aug 6th, 2022

References

External links

{{Wiktionary, iridescent cloud
Iridescent cloud gallery – Atmospheric Optics site
–

Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it, with more than 150 Nobel Pri ...

Supplement Cloud types Atmospheric optical phenomena

Etymology

Mechanism

Gallery

See also

References

External links