Circumhorizon Arc and 22 degree Halo Observed Over Buenos Aires, Argentina
December 06, 2015
Photographer: Sergio Montúfar
Summary Authors: Sergio Montúfar; Jim Foster
A magnificent circumhorizon arc and 22 degree solar halo were observed over La Plata, Buenos Aires, Argentina, on November 21, 2015. I was able to view this display for about 30 minutes from 1:10 until 1:40 p.m. Circumhorizontal arcs (CHA) can only be seen when the Sun is high in the sky, above 58 degrees. Therefore, they're most often seen near the noon hour in either hemisphere’s spring or summer. They take shape when sunlight is refracted through the hexagonal ice crystals that compose cirrus clouds; sunlight enters a vertical side face of a crystal and exits through a lower basal face.
Photo Details: Camera Model, NIKON D5100; ISO Speed Ratings, 160; Shutter Speed, 1/250 second; Aperture, ƒ/22; Focal Length, 18 mm.
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