Today is Winter Solstice. The shortest day of the year.
In the Northern Hemisphere, the winter solstice occurs either December 21 or 22, when the sun shines directly over the tropic of Capricorn.
Yule or Yule-tide is a winter festival that was initially celebrated by the Germanic peoples as a pagan religious festival, though it was later absorbed into, and equated with, the Christian festival of Christmas.
During Winter Solstice until New Years you may hear Christians wish one another warn Yuletide Greetings.
At the same time this day is called Shab-e Yald? (????) and is celebrated in Iran without being part of Christmas.
However you celebrate, it is the first day of winter!
-Reg