December 21 is the winter solstice, the first day of winter, and the shortest day of the year. Here are science, history, and short video explanations of the celestial mechanics involved, plus descriptions of the concurrent celebrations of Saturnalia and Halcyon Days.
The 1914 Christmas truce.
The classic Christmas drunken fruitcake recipe: Check the whiskey. Pour one level cup and drink. Repeat.
That Christmas when Parisians Ate the Zoo.
ICYMI, most recent links are here, and include the pre-Seinfeld origins of Festivus, Rudolph the Red-Nosed Reindeer’s origin story, and that time Santa Claus took the Union’s side in the Civil War.