Sundog Halo, iPhone Shots, Minneapolis, Minnesota, December 2013, photo © 2013 by Liz Anne Schultz. All rights reserved.
in a dark world—
her crystal face, silent, skewed.
Deviant rays of red and blue,
diamond dust takes many hues.
There were two days last week when sundogs appeared on our drive to work, adding a little magic to the sub-zero skies. Sundogs, parhelia, are formed by plate crystals high in the cirrus clouds. Though all crystals refract light from the sun’s rays, we only see those that tilt their light toward our eyes 22° or more from the sun and at the same altitude (a 22° circular halo).
When plate crystals drift down with their large hexagonal faces almost horizontal, rays that become sundogs enter a side face and leave through another, inclined 60° to the first. The refractions deviate the rays by 22° or more, depending on their angle when they enter the crystal, making them visible to us. Red is deviated least, giving the sundog a red inner edge.
Sundogs are visible all over the world, any time of year, regardless of the ground temperature. In cold climates, the plates can reside at ground level as diamond dust. The oldest known account of a sundog is “Sun Dog Painting” (Vädersolstavlan) depicting Stockholm in 1535 when the skyscape was filled with white circles and arcs crossing the horizon. The original oil on panel painting, traditionally attributed to Urban Målare, is lost, and virtually nothing is known about it. A copy from 1636 by Jacob Heinrich Elbfas is held in Storkyrkan in Stockholm, and believed to be an accurate copy.
-posted on red Ravine, Monday, December 9th, 2013