Diamond Dust
Halos - Imaged by Franck Schwitter at 2000m plus in Crans Montana, Switzerland.
Diamond dust, ice crystals glinting and swirling all around in the
cold air, produces some of the very finest displays.
Those seen near ski resorts are often artificial, produced by wind-blown
crystals from snow machines. These halos were fully natural as no machines
were operating.
The lower circle
is a 22 degree halo topped by a "gull's wing" upper
tangent arc made
by horizontal column crystals. The same crystals made the large downward
curving arc at top - a supralateral arc. Touching the supralateral and
curving upwards is a brightly coloured circumzenithal arc made in this
display by plate crystals.
Supralateral and circumzenithal arcs are broader with more apparent
colour because the rays forming them pass between crystal faces tilted
90° to
each other. Compared to the smaller 60° face inclination of sundog and
22 degree rays, the colours are spread wider apart in the sky.
Image ©Franck Schwitter, shown with permission.
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