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 Origin of the Myth of the Poisonous Poinsettia. Related, why we kiss under the mistletoe and how the plant got that strange name (spoiler - it literally means "dung twig").
The 1914 Christmas truce.
The classic Christmas drunken fruitcake recipe: Check the whiskey. Pour 1 level cup and drink. Repeat.
That Christmas when Parisians Ate the Zoo.
10 Important Facts About A Christmas Story's Leg Lamp. Related: Ralphie teamed up with Flash Gordon in a deleted scene from A Christmas Story.
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.