Bishop's ring (d-040501-009)
In gallery: Photos of the month (2004)
Related photos: Atmospheric optics
If you look carefully at the sky coloration in this photo, you may notice circular color bands around the location of the sun. There is a general brownish color near the sun, bordered by greenish. This phenomenon is called Bishop's ring, and is usually caused by volcanic dust at high altitudes. The dust diffracts the sunlight, like the regular cloud corona, but the dust is much smaller than cloud droplets. As a result, Bishop's ring has a much larger radius (around 15 to 30 degrees) than a cloud corona. It is a relatively rare occurrence.
Photo taken with Nikon D100 digital SLR camera, on May 1, 2004, in Socorro, New Mexico (USA).