Halo Complex Above San Francisco
September 09, 2006
Near the top of my list of things to see has been atmospheric halo complexes. So my pleasure was great when a friend phoned me earlier this summer and told me to look at the sky. Clearly visible in the early evening sky above San Francisco was a handsome 22-degree halo as well as three interesting but faint arcs -- a tangent arc, a supralateral arc and a circumzenithal arc (from bottom to top). Can you spot them on the photo? The supralateral arc and circumzenithal arc are indeed very dim but can be detected if you know what you're looking for. See http://elenzil.com/esoterica/halos for labels.
Halo complexes are produced by microscopic crystals of ice high in the atmosphere, which magically tend to orient themselves in the same direction, thus acting as a field of tiny aligned prisms. Thanks to Les Cowley (Atmospheric Optics) for confirming my identification of the above mentioned arcs. Photo taken on June 1, 2006.