The winter solstice can occur anywhere from December 20 to 23. This year it will be Sunday, December 21. This demarks the point when the axis of the earth’s rotation is tilted farthest from the sun in the northern hemisphere. This produces the shortest day and longest night of the year.
The change in the angle of the earth’s axis is what generates the seasons. It gets cold in the wintertime in the northern hemisphere because the tilted axis mean the suns rays are less effective at warming the surface of the earth. This is caused by two effects. Shorter days simply mean less sunlit time, and the sunlight we do get in the winter is weaker because the sun’s rays strike earth at a shallower angle.
We can mark time by observing the sun’s angle. Between the winter solstice and the summer solstice the sun gradually rises higher in the sky every day. The word solstice is from latin and means sun stand. It’s the point when the northerly or southerly movement stops and reverses.
The changing seasons have obvious effects which are important to all life on earth. The need for light, shelter and food all vary with the seasons. Ancient societies, even stone age societies monitored the sun’s angle to keep track of passing seasons.
Stonehenge, in southern England, was built around 2,000 BCE. It’s massive stones are arrayed such that on the equinoxes and the solstices, the sun rising over the horizon appears to be aligned between the gaps. This is doubtless not an accident. Similarly the citadel of Machu Picchu, built high in the Peruvian Andes, was dedicated to the sun god.Within the temple is a semicircular room with a window aligned for observance of their winter solstice in June.
The winter solstice was always a time of celebration as the sun starts its northerly climb, and the days begin again to get longer, not shorter. The Feast of Juul was a pre-Christian festival observed in Scandinavia around the time of the winter solstice. Fires were lit to symbolize the heat, light and life-giving properties of the returning sun. A Yule or Juul log was brought in and burned on the hearth in honor of the Scandinavian god Thor.
In ancient Rome the winter solstice was celebrated with Saturnalia, a seven day event meant to honor Saturn, the god of seed and sowing. A novel feature of the celebration was the suspension of normal social order. Government offices closed, legal restrictions on things like gambling were suspended, and masters served slaves. Gifts were exchanged among family and friends, especially candles which signified the return of light.
Saturnalia, later called Brumalia, from bruma, the “shortest day,” was celebrated for centuries. By about the 4 century CE as Rome came under christian rule, the festival morphed into Christmas celebrations. It is thought that the tradition of gift giving at Christmas is relic of the winter solstice.