The name for the festival of the Winter Solstice in Druidry is Alban Arthan, which means The Light of Arthur.
Some Druid Orders believe this means the Light of the hero King Arthur Pendragon who is symbolically reborn as the Sun Child (The Mabon) at the time of the Solstice. Others see the Light belonging to the star constellation known as the Great Bear (or the Plough) – Arthur, or Art, being Gaelic for Bear. This constellation shines out in the sky and can symbolize the rebirth of the Sun. At this point the Sun is at its southernmost point almost disappearing beyond the horizon, and the days are at their shortest. This was a time of dread for the ancient peoples as they saw the days getting shorter and shorter. A great ritual was needed to revert the course of the sun. This was probably calculated by the great circles of stone and burial grounds which are aligned to this festival, such as Newgrange in Co. Meath, Eire. Sure enough, the next day the Sun began to move higher into the sky, showing that it had been reborn.
This time of year is very cold and bleak, which is why so many celebrations are needed to help people get through the Winter months. It is significant that many civilizations welcomed their Solar Gods at the time of greatest darkness – including Mithras (the bull-headed Warrior God), the Egyptian God Horus and, more recently, Jesus Christ.