Winter Solstice and Pandemic Diversions

The 2021 Winter Solstice was yesterday, December 21, 2021. A new year starts! The Sun comes back. Stormy and I have celebrated the winter solstice since we first learned about solstices in an astronomy course Stormy took at Santa Barbara City College many years ago. The winter solstice always seemed to me to be a more natural marker of time than the calendar new year. Solstices are related to something physical—something real. The winter solstice (in the Northern Hemisphere) is when the Earth’s axis reaches its maximum tilt away from the Sun. As a result, the Sun stays low in the sky all day long. Yesterday, in Colorado Springs, the Sun never got more than 28° above the horizon. After the winter solstice, the days get longer, and Sun gets higher in the sky every day.

Tracking the Sun

A few years ago, during the winter solstice, Stormy and I talked about how long the shadows were at midday. We decided to see if we could see the change in the length of midday shadows from day to day. So we mounted a gnomon (otherwise known as a long stick) in our back yard and measured the length of its shadow at midday every day we were home. Sure enough, we found the shadows got shorter every day. Okay, we weren’t surprised, but it’s always nice to actually see that the world behaves as expected.

Like many of you, the pandemic forced Stormy and me to be home every day during 2020. As a result, we had an opportunity to pretend to be druid astronomers. We could carefully measure the location of the tip of the gnomon’s shadow every day at 12:00 noon MST. Stormy drew the line at wearing golden robes while we executed our observations. (She would have worn a pointy hat with stars, though.)

The movie below is a time-lapse taken on the Winter Solstice 2020. Part way through the video, you see us mark the shadow and make our measurements.

I felt like a character out of Neal Stephenson’s book Anathem as we measured the shadow and marked its position on the ground. Like the characters in the book, we were charting the position of the Sun with crude astronomical instruments—a stick and a ruler. On the cover of that book is a figure-eight-shaped pattern. That pattern is called an analemma. An analemma shows the Sun’s position in the sky at a fixed time, as seen from a fixed location. That is precisely the shape we created when we connected the dots from our measurements.