There is some confusion as to the meaning of the date “December 25th,” with some claiming that is not part of the winter solstice. This contention is erroneous, however.
The reality is that the ancients celebrated winter festivals from the last half of November until the first half of January. The solstice celebrations such as Saturnalia lasted for several days, from the 18th to the 23rd.
In this mix, several ancient cultures viewed the solstice – a word meaning “sun stands still” – as lasting for THREE DAYS. So, for three days they said the sun was doing a “stutter step” on its journey northward (from a geocentric perspective in the northern hemisphere).
Thus, the period of the sun standing still would BEGIN on December 21st at midnight and end on December 24th at midnight, heralding the “birth” of the “new sun” on the next day, December 25th.
As astronomer Dr. Edwin C. Krupp explains:
Solstice means “sun stands still,” but the sun isn’t really still at the winter solstice. It rises and sets the way it does every day. But for a few days at the time of the solstice, the sun’s walk-on is a repeat performance. If you watch the sunrise for several days in a row, both before and after the winter solstice, you notice that the rising point scarcely changes from day to day. This repetitive rising is what inspired the idea of the solstice. Because the sun runs the same race on several successive days in what the ancient Germanic peoples called the “wet,” or winter, season, the event is called the winter solstice; it takes place on or within a day of December 21.
(Krupp, Edwin C. Beyond the Blue Horizon: Myths and Legends of the Sun, Moon, Stars and Planets. Oxford: Oxford University Press, 1991; 83)
The image of December celebrations from our 2010 Astrotheology Calendar illustrates the abundance of “light festivals” commemorating the winter solstice throughout the month.