ELi on Earth: Winter Solstice

Image of the Newgrange passageway on the winter solstice, courtesy World Heritage Ireland

Winter solstice comes to East Lansing this year at 11:49 p.m. tonight, Monday, December 21. At that time, the earth’s tilt away from the sun (for those of us in the Northern Hemisphere) will be at its maximum. From that moment until the summer solstice in June, the Northern Hemisphere will tilt more and more toward the sun.

The solstice is astronomically determined by the position of the sun in the sky more than the length of any particular day or night. The word “solstice” means that the sun (sol) stands still (sistere). If you plot the position of the sun in the sky at noon each day, the sun gets lower in the sky each noon until the winter solstice, at which point the sun’s position stops moving lower. Thereafter, the noontime position of the sun gets higher in the sky each day until the summer solstice, when the sun reverses and starts getting lower again.

The exact point of the winter solstice is when the sun is its most southern point. This year that will happen almost exactly on other side of the earth from East Lansing. At noon on December 22 in the Indian Ocean in the Southern Hemisphere, the sun will be directly overhead at the Tropic of Capricorn (due south of Aceh, North Sumatra). At the same time, it will be 11:49 p.m on December 21 in East Lansing.

You can find out more about how the solstices are measured from our coverage of the summer solstice.

Finding the exact time of the solstice is a modern phenomenon. Measuring the solstice to a single day requires the observer to measure the position of the sun to one-sixtieth of its diameter or the time of sunrise to within 1-2 minutes. In the past, people built huge structures to successfully determine and celebrate the day of winter solstice. More than five thousand years ago, people built the tomb at Newgrange, Ireland, and oriented it toward the sunrise on the winter solstice. Stonehenge in England, the Goseck circle in Germany, medicine wheels and other petraforms in North America, and other ancient sites on every continent have structures that could have been used to track the solstices to within a day.

For those in the northern latitudes, the winter solstice marked the onset of longer days and was a stable day from which to determine planting times or times for slaughtering animals. The first snow could be early or late, and the lunar calendar does not follow the seasons, but the winter solstice is always at the same point in the seasons.

Traditional holidays tend to cluster around the winter solstice. Many cultures have considered the longer days something to celebrate. There may also have been practical reasons to slaughter animals at that point in the year, as they would not have to be fed over the winter. And the time it takes fall fruit to ferment into alcohol may have led to feasting and celebrating around the time of solstice.

Regardless there are a lot of current and historical winter solstice holidays: Soyal (Hopi Indians), Yalda (Persians/Zoroastrians), Inti Raymi (Incas; their winter solstice was in June), Saturnalia (Romans and current Roma), Dong Zhi (Chinese), and the pre-Christian Yule celebration of Germanic and Norse people.

From all of us here at ELi, enjoy the longer days.