From Writers' Almanac Today

In the northern hemisphere, today is the Winter Solstice, the shortest day of the year and the longest night. It's officially the first day of winter and one of the oldest known holidays in human history. Anthropologists believe that solstice celebrations go back at least 30,000 years, before humans even began farming on a large scale. Many of the most ancient stone structures made by human beings were designed to pinpoint the precise date of the solstice. The stone circles of Stonehenge were arranged to receive the first rays of midwinter sun.

Ancient peoples believed that because daylight was waning, it might go away forever, so they lit huge bonfires to tempt the sun to come back. The tradition of decorating our houses and our trees with lights at this time of year is passed down from those ancient bonfires.