My parents were married on the solstice 67 years ago and took a lot of ribbing from their friends for their choice of nights to marry.
On the winter solstice the sun begins its northern migration and brings with it that oh so precious commodity, light. The sun appears at its lowest point in the sky, and at midday its elevation appears to be the same for several days before and after the solstice. The ancients believed that on this date the sun and the moon stopped their flight across the heavens and the sun was reborn of the goddess.
It is the oldest winter celebration in the world. Ancient Egyptians worshipped the sun rebirth, and, over 4,000 years ago, the Irish built a tomb designed to allow light in only during the solstice. Christian religions have incorporated the rituals in the hopes of converting the Olde Believers and those traditions are still celebrated today as Christmas. The Yule log, wreathes, stars on the tops of Christmas tress, even the tree itself are all symbols of the former solstice celebration.
But I did not know, until recently, that this is where the Yin Yang symbol came from that is so often seen in the Buddhist traditions.
Ancient Chinese scholars discovered changes in the year associated with the sun (Yang) and the moon (Yin). They used an 8-foot pole and the shadow of the constellation The Big Dipper to establish the position of the sun in different seasons. They also established the number of days in a year, and through elaborate calendars established the vernal, and autumnal equinox, as well as the summer and winter solstice. Using a circular calendar and shading in the summer and winter months the yin yang sign emerges.It is often seen with a small dot in at the top and bottom of the symbol; this indicates the winter and summer solstice.
So, whether you are pagan, Buddhist, Jewish, Muslim, or Christian, it is a day of celebration of the renewal of life, a circle of continued rebirth.