August 28, 2004
The photo above showing an enchanting cloud corona was captured near Berkeley, California on July 17, 2004. Like all coronae, the cloud corona is a diffraction phenomenon, which results from the interference of sunlight (or moonlight) about water droplets. Smaller droplets cause larger diffraction angles and a larger corona. Another characteristic of coronae is that their light is unpolarized, indicating that no reflections are involved. The cloud corona is sometimes mis-identified as a rainbow, but unlike rainbows, coronae form in the vicinity of the Sun. See also the Earth Science Picture of the Day for October 16, 2003.