December 21

The real reason for the season. No, not Jesus, but the Sun, not to be confused with the Son (of God). It's the shortest day / the longest night of the year. It marks the beginning of winter. On the night of Winter Solstice, as seen from a northern sky, the three stars in Orion's Belt align with the brightest star in the eastern sky Sirius to show where the Sun will rise in the morning. Hello people? Does this story sound familiar? How about those three "wise men" following the bright star to the "birth" of the savior? In a way it is like the sun is being born because after sinking to it's lowest point in the sky, it begins it's descent into the northern sky and the days grow longer. I'd say it's a valid reason to celebrate. December 25 was chosen as Christmas because that date marked the solstice on the Julian calendar. Then in 1582 Pope Gregory XIII moved things around by like .0122 days (the Gregorian Calendar) and it got shifted to the 21st. 

Here is what Jesus looks like in Japan, except he is a Sun Goddess named Amaterasu and not not some kid whose mom claimed to be a virgin.

Also, in olden times people in colder climates like Europe would typically celebrate this holiday as a last feast of the season before the famine/starvation months of January-April. Many livestock were slaughtered so they wouldn't have to be fed during the coming months, so there was a large supply of fresh meat. And the majority of beer and wine made during the year was finally fermented and ready to drink. Good times!