August 10, 2007
This magnificent pair of sundogs (parhelia) was observed around mid-day behind our communication dome and radio antenna at the Halley Research Station in Antarctica. They formed from suspended or slowly falling ice crystals in the lower atmosphere (diamond dust). In order for sundogs to be seen, hexagonal plate-shaped ice crystals must be aligned with their flat faces horizontal. Note that even near mid day, the Sun is low in the sky in the Antarctic. Photo taken on April 4, 2007 (latitude 76 degrees south, longitude 26 degrees west).
Of special interest is the presence of additional arcs and halos, which though not near as obvious as the sundogs can nonetheless be detected. These include the 22 degree halo, parhelic circle, a Sun pillar, and a faint upper tangent arc. Moreover, it appears that very rare Lowitz arcs can be discerned on this truly remarkable photo. These curious arcs can only form when ice crystals are spinning. For more about these arcs see the Atmospheric Optics link below.