Barigui Circumzenithal Arc, Brazil
October 04, 2008
The photo above shows a crescent-shaped strip of spectral colors known as a circumzenithal arc set off by bands of cirrus clouds. It was taken at 8:13 a.m. on April 29, 2007, from Barigui Park. This is an ecological reserve that lies two miles (3.2 km) from the center of Curitiba (population nearly two million) in Southern Brazil. In order to see circumzenithal arcs, the Sun must be low in the sky, so that its rays can enter the crystals’ upper basal plane and exit through a side face. These striking arcs are better defined than the colors in a rainbow.