A solstice, as defined by the dictionary is "a furthest or culminating point; a turning point". The winter solstice occurs when the sun is furthest from the celestial equator (a theoretical projection of the earth's equator into space).
Technically, the winter solstice lasts for only the instant of time during which the sun is at its furthest. However, "winter solstice" typically refers to the entire day. In the Northern Hemisphere the day of winter solstice is the shortest day of the year and the point at which days begin to lengthen. This usually occurs on the 21st or 22nd of December.
There are much more fascinating aspects to the winter solstice, however. For thousands of year the winter solstice has been associated with religious and philosophical importance. Around 46 BC, the 25th of December was established as the winter solstice. At that time the Julian Calender (named after Julius Ceasar who first introduced it) was in used and, when the Gregorian calendar was introduced (around 1582) the date was changed to the 21st.
|The Oak King of Winter Solstice|
In ancient Japan the winter solstice was believed to be the time when the sun goddess Amateras emerged from her cave. The Incas held winter solstice celebrations in honor of Init, the sun god. In Germany, the winter solstice was a time of celebration for Hertha, the Norse goddess of light. The Roman celebration of Sol Invictus, the Roman deity of the sun was held on December 25th and represented the rebirth of the sun.
Interestingly, there are many parallels between these celebrations and Christmas. Traditionally, Christians celebrate Christmas as the day of the birth of the Son of God. There are more than just phonetic similarities, however. In John chapter 9, verse 5, the Holy Bible refers to Jesus Christ as "the light of the world". The Christmas celebration of the birth of the "light of the world" coincides with the metaphorical, annual, "rebirth of the sun".
Some Christian fundamentalists shy away from celebrating Christmas due to its concurrence with the Roman celebration of Sol Invictus. However, it is an oversimplification to say that Christmas started as a pagan tradition. The word "Christmas" is derived from "Christ's mass" and first appeared in 1038. But, Christian celebrations of Jesus' birth began long before---sometime around 200 AD. The date of December 25th coincided well with the celebration of the Epiphany (a January 6th celebration of the magi's visit to Jesus) as well as being exactly nine months from the traditional date of the Incarnation. The winter solstice has, for thousands of years, been celebrated as a time of new beginning and rebirth. Whether the Christmas tradition stems directly from winter solstice celebrations or if the two merely coincide will most likely never be fully known. Either way, the winter solstice is a time for reflection and rebirth---something nearly everyone agrees the world is in need of.