February - halos You are here: Home Photo gallery Atmospheric optics Twilight phenomena Purple red

The purple red is a purple to red sky coloration sometimes visible about 15 to 30 minutes after sunset. It is caused by fine aerosols in the atmosphere, deposited there by volcanic eruptions. During the great Krakatoa eruption around 1880, many years followed with intense sunsets and extensive purple red skies. Sunlight, deeply reddened by atmospheric absorption and Rayleigh scattering, shines on the high stratum of aerosols on its under-surface. Together with the deep blue clear sky this shows like a purple veil.

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