Tonight’s Full Cold Moon is aptly named. We’re now firmly footed in winter and the only way to spring is forward by clock and calendar. The actual moment of full moon occurred this morning at 4:21 a.m. (CST), making the lunar visage slightly fuller last night than it will be when darkness falls tonight. December’s moon rides high across the sky since it’s opposite the low winter sun.
Along with the new season come the ice crystals and the wonderful assortment of halos and pillars they form. Sometimes ice phenomena are obvious as when a car approaches your direction at night accompanied by tall beams of light shooting straight up into the air above its headlights. Ice crystals create similar “light pillars” above and below the sun and moon. These range in visibility from subtle to grand.
In what appeared to be a nearly clear, blue sky Wednesday, I happened to walk by a building which blocked the sun’s over-bright disk from view. There above it a fat spike of light extending upward for 20 degrees or more.
Last night I drove home after shooting photos of a basketball game in Hibbing north of Duluth with the moon and radio my only company. Soon enough I noticed something odd about how the light was distributed about the moon, which shone through a thin layer of cloud.
Instead of being surrounded by a glowing aureole of light, feathers of light stuck out directly above and below the moon. Aha! Another light pillar. At the time a very light snow was falling.
All these macro-scale phenomena can traced to billions micro-sized ice crystals in clouds or even in minute snow crystals. As the hexagonal plate and column-shaped ice crystals drift earthward, they tip and tilt. Upper pillars are formed when light is reflected downward toward our eyes from the bottom side of the plates; lower pillars when light is reflected upward from the topmost crystal faces. The most striking pillars are often seen at sunset when a front is approaching, bringing with it a veil of cirrus clouds in the west.
When crystals are nearly perfectly horizontal, a narrow column results, but when they’re tilted at a variety of angles to the horizontal, pillars spread into broad feathers like the one I saw around the moon.
Other halos, including the more common “ring around the sun” or 22-degree halo, are formed when light refracts through hexagonal, pencil-shaped ice crystals. Rarer smaller halos originate in pyramidal ice crystals.
You’ll always find something interesting happening in the sky by both the smallest and biggest things nature can muster. For more on light pillars and ice halos, head over to The Weather Doctor site.
PS. I had hoped to give you all a sneak preview of 2013 astronomy events but am still waiting for a few pieces of information. Watch this space – it will appear soon!