Have a Merry and Prismatic Christmas!
A partial solar halo made of "diamond dust" brackets the sun on Christmas Eve morning from Duluth, Minn. A faint sun pillar (vertical glow above the tree) is also visible and forms when light reflects off the bottoms of ice crystals floating parallel to the ground. Bob King Last night's winter storm and plummeting temperatures left us with piles of snow and dazzling sunshine this morning. As I heaved shovelfuls of the stuff to clear a path to the driveway, I caught sight of an arc of rainbow light between the trees. It turned out to be part of a rare diamond dust halo. Ordinarily, a halo forms when minute, hexagonal ice crystals in cirrostratus clouds refract sunlight or moonlight into a circle with a radius of 22°. But no such clouds streaked the sky this morning. Instead, nearby but invisible ice crystals suspended in the -8° F air took it upon themselves to do the refracting. The halo was partial — twin, arc-shaped stubs — with a hint of the complete semicircle wrapp...