A corona is an optical phenomenon, classed as a photometeor, produced by the diffraction of sunlight, moonlight or another bright light source by individual particles, such as water droplets in clouds or ice crystals, that are larger than the wavelength of light. It typically appears as a set of concentric, pastel colored rings surrounding the light source, with a bright central region called the aureole. The rings form because diffracted light waves reinforce each other at some scattering angles and cancel out at others, producing alternating bright and dark bands around the source.
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