Arctic Ice Crystals over Yellowknife

Photo showing a simultaneous 22-degree halo, upper tangent arc and sun pillar taken on Dec 22 2013 at Yellowknife, just before noon, as the sun poked its head slightly above the horizon for a brief few hours. These are due to ice-crystals formed in super-saturated air. At modest degrees of supersaturation, and temperatures just below 0C, ice crystals are hollow and solid hexagonal cylinders, while at temperatures below -10C, they become largely hexagonal plates. At higher levels of supersaturation, the crystals become dendrites (essentially snow-flakes). The upper tangent arc is due to refraction of sunlight through horizontally aligned hexagonal cylinders, aligned in this way due to their gently fluttering downward movement. The central sun-pillar is due to reflection from horizontally aligned hexagonal plates, also fluttering gently downward. The 22-degree arc is due again to hexagonal columns, but this time ones that have conglomerated together in clusters, so there is no particular alignment as they tumble downward. Sundogs were visible further the left and right (outside the picture). The raven gives the photo a distinctly Yellowknife flavour.

Wayne Hocking
Second Prize ( 2014 Open Category )
Back to Art of Physics page
Questions or comments regarding these pages may be sent to