101 Things To Do: The Swensen Sundial in River Falls
Editor's note: This is the latest stop in our new series, 101 Things To Do. Each week through December 2020, we will select one place or activity around the region to highlight. The stories are compiled at www.rivertown101.com.
At a glance, the metal framework on the south side of the E.H. Kleinpell Fine Arts Building on the campus of the University of Wisconsin-River Falls appears to be a nice, symmetrical sculpture. It is, but it is also a very precise, vertical sundial.
Built in 1995 in honor of Dr. Richard D. Swensen, retired dean of the College of Arts and Sciences, the sundial was designed by retired physics professor Dr. John Shepherd.
Shepherd designed the sundial by starting with the straight line running horizontally through the middle of the sundial which represents the vernal and autumnal equinoxes.
"The vernal equinox was the key to most calendars," Shepherd explained. "The sun's shadow actually does move in a straight line on those days."
Two other important lines are the curved lines at the top and bottom of the sundial. "The top one is the winter solstice, and the bottom one is the summer solstice," Shepherd said.
As he designed the sundial, Shepherd noticed that there was a lot of open space in the middle so he added in two other curved lines based on "what we call the megalithic calendar," he said. "They had the year divided into eight parts."
As the sun shines on the wall, the pointer or gnomen casts a shadow which varies in angle by the time of day and length by the time of year.
"The earth's orbit around the sun is elliptical," Shepherd said. "It is closest to the sun, not in the summer as most people think, but in January. That is a small effect compared to the tilt of the earth. That's what determines the seasons. That makes the sun move up and down in the sky and therefore makes the shadow move up and down. In the summer, the shadow will be all the way down to the bottom line, and at about Christmas, it will be all the way up to the top line."
The variation in speed around the sun also creates a need for a sundial to make corrections of several minutes throughout the year. Shepherd compensated for that by using figure 8s called analemmas, which have a dark side and a light side.
"In the spring, after Christmas, the hour will be on the light side," Shepherd said. "In the fall, the hour is on the dark side. That allows you to read it to about a minute of accuracy."
If you go...
What: The Swensen Sundial
Where: 420 E. Cascade Ave., River Falls, WI 54022
When: Daylight hours every day
How much: Free
An earlier version of this story misspelled the name of the sundial in the headline.