The Winter Solstice happens at exactly 5:47pm UTC time today. The earth's axial tilt is farthest away from the sun at its maximum of 23° 26'. The seasonal significance of the Winter Solstice is in the reversal of the gradual lengthening of nights and shortening of days.
The solstice itself may have been a special moment of the annual cycle of the year even during neolithic times. Astronomical events, which during ancient times controlled the mating of animals, sowing of crops and metering of winter reserves between harvests, show how various cultural mythologies and traditions have arisen. The primary axes of both of the monuments at Stonehenge in Britain and New Grange in Ireland seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (New Grange) and the winter solstice sunset (Stonehenge). The winter solstice may have been immensely important because communities were not certain of living through the winter, and had to be prepared during the previous nine months.
For more about how cultures around the world celebrate this event click here.