November - fog You are here: Home Photo gallery Atmospheric optics Ice crystal halos 20o halo


A halo around the sun or moon with a radius of 20 degrees, caused by refraction of light by randomly oriented pyramidal ice crystals. On the photo at the left, it is very faintly visible between the very bright 22-degrees halo and the faint 18-degrees halo. On the photos, look to the upper right of the sun; there, it is most pronounced.

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