Today (17:11 UTC) marks the winter solstice, the shortest day and longest night, and the onset of winter in the Northern Hemisphere. You can see the gradual lengthening of days, second by second, here. The winter solstice occurred this year in the Southern Hemisphere on June 21.
On this day, Stonehenge is a magnet for tourist groups, neo-pagans, Wiccans and neo-Druids. From Stonehenge Tours:
Stonehenge is carefully aligned on a sight-line that points to the winter solstice sunset (opposed to New Grange, which points to the winter solstice sunrise, and the Goseck circle, which is aligned to both the sunset and sunrise). It is thought that the Winter Solstice was actually more important to the people who constructed Stonehenge than the Summer Solstice. The Winter Solstice was a time when most cattle were slaughtered (so they would not have to be fed during the winter) and the majority of wine and beer was finally fermented.The exact time for the Winter Solstice is December 21st, 17.11pm (UK time).
Image Source: Mount Washington Observatory via Greetings May All Your Dreams Come True.
Image Source: Out of Ashes.