Cloud iridescence or irisation is a

colorful Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associa ...

optical phenomenon Optical phenomena are any observable events that result from the interaction of light and matter. All optical phenomena coincide with quantum phenomena. Common optical phenomena are often due to the interaction of light from the sun or moon wit ...

that occurs in a

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

and appears in the general proximity of the Sun or

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. The colors resemble those seen in

soap bubble A soap bubble is an extremely thin 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 before bursting, either on their own or on contact wi ...

s and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in

altocumulus Altocumulus (From Latin ''Altus'', "high", ''cumulus'', "heaped") is a middle-altitude cloud genus that belongs mainly to the ''stratocumuliform'' physical category characterized by globular masses or rolls in layers or patches, the individual ele ...

, cirrocumulus,

lenticular Lenticular is an adjective often relating to lenses. It may refer to: * A term used with two meanings in botany: see * Lenticular cloud, a lens-shaped cloud * Lenticular galaxy, a lens-shaped galaxy * Lenticular (geology), adjective describing a ...

, and

cirrus cloud Cirrus ( cloud classification symbol: Ci) is a genus of high cloud made of ice crystals. Cirrus clouds typically appear delicate and wispy with white strands. Cirrus are usually formed when warm, dry air rises, causing water vapor deposition on ...

s. 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 A pastel () is an art medium in a variety of forms including a stick, a square a pebble or a pan of color; though other forms are possible; they consist of powdered pigment and a binder. The pigments used in pastels are similar to those use ...

, but can be very

vivid Vivid may refer to: Music * Vivid (band), a Japanese rock band * "Vivid" (song), by Electronic, 1999 *"ViViD", a 2016 song by Loona from '' HeeJin'' Albums * ''Vivid'' (Vivian Green album), 2015 * ''Vivid'' (Crystal Kay album), 2012 * ''Vivi ...

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 a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when ...

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 A curved mirror is a mirror with a curved reflecting surface. The surface may be either ''convex'' (bulging outward) or ''concave'' (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are ...

or in a pool of water.

Etymology

Irisations are named after the Greek goddess Iris, goddess of

rainbow A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...

s and messenger of

Zeus Zeus or , , ; grc, Δῐός, ''Diós'', label= genitive Boeotian Aeolic and Laconian grc-dor, Δεύς, Deús ; grc, Δέος, ''Déos'', label= genitive el, Δίας, ''Días'' () is the sky and thunder god in ancient Greek relig ...

and

Hera In ancient Greek religion, Hera (; grc-gre, Ἥρα, Hḗrā; grc, Ἥρη, Hḗrē, label=none in Ionic and Homeric Greek) is the goddess of marriage, women and family, and the protector of women during childbirth. In Greek mythology, she ...

to the mortals below.

Mechanism

Iridescent clouds are a

diffraction Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

phenomenon caused by small water droplets or small

ice crystals Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. Formation The hugely symmetric shapes are due to depositional growth, n ...

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:Iridclouds2.jpg File:IridescentCloudArran.jpg File:Stratocumulus fibrous fishscali-1.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:Irisation or iridescence in super-cooled cloud - NOAA.jpg, Irisation or iridescence in super-cooled cloud droplets in cirrocumulus clouds. File:Iridescent Cirrus behind Stratocumulus over Warsaw, June 26, 2005.jpg, Irisation in cirrus (or maybe cirrocumulus) clouds behind

Stratocumulus A stratocumulus cloud, occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus, and th ...

(bottom), in the afternoon over Warsaw, Poland. 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

Iridescent cloud gallery - Atmospheric Optics site
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Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...

Supplement Cloud types Atmospheric optical phenomena {{Cloud-stub

Etymology

Mechanism

Gallery

See also

References

External links