Las Vegas Halo
February 18, 2008
This classic atmospheric halo was observed above Las Vegas, Nevada on the morning of November 2, 2007. The expression "What happens in Vegas stays in Vegas" shouldn't apply to phenomenon such as this -- it's certainly worth sharing. Cirrostratus clouds, shown above, are composed of floating hexagonal ice crystals, which when more or less randomly oriented (and pencil-shaped) may yield the 22 degree solar halo and the circumscribed halo as well.
The 22 degree halo (radius in degrees from the Sun) is caused by the minimum deviation of sunlight or moonlight through aligned ice crystals. Essentially, light passing at or just near the minimum deviation angle is focused into a narrow range of angles of sufficient brightness to render a halo of colored light.