From National Geographic:
The solstices occur twice a year (around December 21 and June 21), because Earth is tilted by an average of 23.5 degrees as it orbits the sun—the same phenomenon that drives the seasons.
During the warmer half of the year in the Northern Hemisphere, the North Pole is tilted toward the sun. The northern winter solstice occurs when the "top" half of Earth is tilted away from the sun at its most extreme angle of the year.
Being the shortest day of the year, the winter solstice is essentially the year's darkest day, but it's not the coldest.
Because the oceans are slow to heat and cool, in December they still retain some warmth from summer, delaying the coldest of winter days for another month and a half. Similarly, summer doesn't hit its heat peak until August, a month or two after the summer solstice.
That's neat, but did you know that many people out there also decide to replace most traditional holidays during this time of year to celebrate the winter solstice? And with good reason, since celebrating the winter solstice has been a tradition for a while.
From the same article:
Germanic peoples of Northern Europe honored the winter solstice with Yule festivals—the origin of the still-standing tradition of the long-burning Yule log.No doubt, there is some correlation between the winter solstice, and the December 25th holiday, Christmas. I for one, as I have already mentioned, don't care which one people choose to celebrate. I also am not amused at whether or not Christmas is just a ripoff of the celebration of the winter solstice; however, I am interested in the Lovecraft ripoff of the song "Joy to the World".
The Roman feast of Saturnalia, honoring the God Saturn, was a weeklong December feast that included the observance of the winter solstice. Romans also celebrated the lengthening of days following the solstice by paying homage to Mithra—an ancient Persian god of light.
Many modern pagans attempt to observe the winter solstice in the traditional manner of the ancients.
"There is a resurgent interest in more traditional religious groups that is often driven by ecological motives," said Harry Yeide, a professor of religion at George Washington University. "These people do celebrate the solstice itself."
Pagans aren't alone in commemorating the winter solstice in modern times.
In a number of U.S. cities a Watertown, Massachusetts-based production called The Christmas Revels honors the winter solstice with an annually changing menu of traditional music and dance from around the world.
"Nearly every northern culture has some sort of individual way of celebrating that shortest day," said Revels artistic director Patrick Swanson. "It's a lot of fun for us to dig up the traditional dance and music and even the plays [honoring] that time of the year."