Cloud iridescence or irisation, terms derived from Iris the Greek personification of the rainbow. When parts of clouds are thin and have similar size

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Cloud iridescence or irisation, terms derived from Iris the Greek personification of the rainbow. When parts of clouds are thin and have similar size droplets, diffraction can make them shine with colours like a corona. In fact, the colours are essentially corona fragments and are caused by small water droplets or small ice crystals individually scattering light. The effect is best seen where the cloud is thin and semi-transparent.

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Photo credit: © DAVID PARKER/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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Keywords: blue, cloud, color, colors, colour, colours, corona, coronal, crystals, diffraction, droplets, ice, iridescence, iris, irisation, primary, prism, prismatic, rainbow, secondary, shine, shining, sky, spectra, spectrum, sun, thin, water