For millennia, humans have celebrated the winter solstice (the actual "reason for the seasons") at this time of year.

National Geographic: Winter Solstice 2009: Facts on Shortest Day of the Year

'Today is the winter solstice and the first day of winter in the Northern Hemisphere. It's all due to Earth's tilt, which ensures that the shortest day of every year falls around December 21.'

Happy Solstice from the Freethinkers of Colorado Springs - and many happy returns to one and all!