The Winter Solstice and the Woman Who Explored the Sun

December 17, 2020

Written by: Vanessa Hennessey

Coming up just around the corner on December 21st is the winter solstice, the shortest day of the year in the northern hemisphere.  It also marks the time when the days become longer as we head out of the winter and into the spring. And while it is a natural phenomenon, occurring every year, it has also been  historically a time of celebration for millennia around the world.


The 2020 winter solstice occurs on Monday, December 21st, at 2:02am pacific time. It happens, of course, at the exact same moment around the world, and you can see what time it will occur in your neck of the woods here. The solstice and the seasons occur because the Earth is tilted 23.5 degrees away from the sun, and as it becomes cooler in the north, the Earth tilts gradually away from the sun. This means that the southern hemisphere becomes warmer and experiences summer when in the north hemisphere experiences winter. The solstice happens when the tilt is at its most extreme angle. (For an easy-to-follow explanation of the seasons, click here.)

The solstice is a rather unimpressive event, as opposed to a lunar or solar eclipse. You probably won’t see any dramatic shifts in the skies, but at noon, shadows made by the sun will be the longest of the year, because the sun’s arc in the sky has been dropping lower and becoming shorter since June. You may also notice that the sun seems to be rising and setting in the same place for the same reason. This is actually how the word “solstice” came to be – it means “sun stands still” in Latin. National Geographic has a great explanation of how a solstice occurs here

Source: Stonehenge Guided Tours

What about those celebrations I mentioned earlier? When we think of winter celebrations, we often think first of Christmas, but Christmas has only been celebrated since 336 AD in Rome (at least, that’s the first time Christmas celebrations were recorded, that we know of). But the solstice has been celebrated even longer than that. In approximately 2500 BCE, the Neolithic people of Durrington Walls built Stonehenge, a prehistoric monument in what is now called Wiltshire, England. It is a ring of standing stones, and is believed to have had a ceremonial function, especially during midwinter. There is another ring of stones called the Southern Circle nearby, as well as the ring of stones that make up Stonehenge. The first ring is oriented to the midwinter sunrise, and is arranged complementary to the orientation of the ring of stones at Stonehenge, which focuses on the midwinter sunset. It is thought that the people who settled here celebrated the “return of the sun” as the days became longer again during the dark, cold winter. Similarly, the ancient Norse people in northern Europe celebrated Yule from the winter solstice to January, to also mark the return of the sun. Fathers and sons would bring home large logs and place them on big bonfires, which is where the term “Yule log” originated. Even the Incan Empire in the southern hemisphere celebrated the solstice, paying homage to the sun god Inti at a winter solstice celebration called Inti Raymi (Quechua for “sun festival”). In Peru, like the rest of the Southern Hemisphere, the winter solstice takes place in June.

Cecilia Payne. Source: Cosmos Magazine

In the northern parts of Europe, Christianity became increasingly popular starting around the 2nd century CE, and the pagans (non-Christians) converted or were forced to convert to Christianity. Historian David Gwynn of the University of London thinks it’s no coincidence that Christmas began to be celebrated on December 25th, as it was closest to the winter solstice, which the ancient pagans would celebrate.

But who figured out what the solstice actually is? The answer to that question is not an easy one, but we do know that in about 830 CE, Caliph Al-Mamun of Baghdad directed his astronomers to measure the obliquity (tilt) of the Earth, and the result was used in the Arab world for many years. In 1437 CE, Ulugh Beg determined the Earth's axial tilt as 23°30′17″ (23.5047°), and as mentioned before, the winter solstice occurs as the Earth tilts further away from the sun. Without the sun, there would be no solstice, and centuries later, a notable woman in science, Cecilia Payne (1900-1979), made a very important discovery about just what the sun - and therefore, other stars - are primarily made of: hydrogen and helium. She made this discovery while in graduate school at Harvard University in Cambridge, Massachusetts. She sent her thesis on this topic to a Professor Russell at Princeton, who said that her result was "clearly impossible," but she persisted and turned her thesis into a book called Stellar Atmospheres, which was well-received by astronomers, and within years, it was determined her results were fundamental and correct. She wrote her doctoral dissertation at Harvard, and was the first person to receive a PhD from Radcliffe College at Harvard. Without Cecilia Payne, we would not have some of the most important information about the foundations of the stars in the universe, and we would not be able to appreciate the sun in all of its glory, including at the solstice!

Back to winter - now, Christmas is an extremely popular winter holiday to celebrate, but it is not the only one. Many people around the world still celebrate the winter solstice. Britannica has a whole list of celebrations that are still practiced today, and some that have lost popularity over the centuries. These celebrations span across the world, from North America, to Europe, to China. In Europe and North America today, many people celebrate the “return of the sun” by lighting candles, observing the subtle shifts in the light outside, committing to a quieter pace of life as the cold settles in, make goals for the coming year, share food together, light Yule logs, and more. The solstice demonstrates the “cyclical order of the cosmos,” and provides an opportunity to celebrate the winter, but inspired by science. As Deena Wade at says, celebrating the solstice “can be a beautiful remembrance that our lives are part of a larger order, always changing, always renewing.”

What are your favourite winter celebrations? Let us know over at our Twitter or Facebook!