Portao, Brazil Halo
April 07, 2007
The eye-catching 22 degree halo shown above was observed over the city of Portao, in southern Brazil, in the state of Rio Grande do Sul. The 22 degree halo (22 degrees in diameter) forms in cirrus clouds composed of pencil-shaped hexagonal ice crystals. These crystals are mostly randomly oriented. Note the darkened area inside the halo, which is a region where light can't be scattered by simple refraction. This photo was captured at 13:30 local time, on January16, 2007. A Nikon D50 camera was used with a 18 mm zoom lens.