22º halo South Pole
22º halo image index South Pole 4th January 1999.  The South Pole is famed for its diamond dust halo displays but this 22-degree halo is in cirrus cloud. Photographed by Marko Riikonen. Note the special purpose sun shield. Crossed polarising filters at its tip let through just enough light to show the disk of the sun enabling precise measurements of the size of halos. Image ©Marko Riikonen, shown with permission.