|Halos at 34,000 ft
Imaged by Tim Stone (Tim's Pix) over NW Illinois.
A 22° halo dominates the view. At left and right are hints of sundogs. Beneath the sun is a long lower pillar that almost reaches the lower tangent arc on the 22° halo.
But the really unusual feature is the faint inner circular halo - a 9° odd radius halo formed by pyramidal ice crystals. The halo was on several images including ones shot through a different window - a necessary precaution when cameras see faint rings around bright objects.
©Tim Stone, shown with permission.
|9° halos are formed by rays entering a central ring face and leaving via an opposite face on the lower ring of pyramidal facets (ray path 3-26).
The two facets are inclined at only 28° compared to the 60 and 90° of the faces that form most halos. The ray passage through the equivalent of a 28° prism to give a minimum deviation angle of 9°