"This is an alchemical time sign for winter."
Learn more at symbols.com.
Winter officially begins at 10:08 p.m. PST tonight, AKA 6:08 a.m. GMT on Saturday.
Here's some information on how different peoples have celebrated, through the ages, the coming of winter and the turning back to the light: religioustolerance.org.
Also, an exciting note from that site:
For the first time, the 2007 Winter Solstice illumination at Newgrange in Ireland will be available live on the Internet, weather conditions permitting. See http://www.newgrange.com. The passage and chamber at Newgrange will be illuminated by the rising sun on 2007-DEC-21 between 08:58 and 09:15 GMT.