By Ryan Hurtgen
In my youth, we had a boat named The Salty Mae at my grandparents’ cabin on Table Rock Lake. Table Rock is a big lake, with lots of long coves with nothing but wilderness. You can ride for hours and hours exploring it. The Salty Mae was a 1970’s orange cruiser, perfect for zipping up and down the lake on day trips. Granddad named it after my Grandma Mae, whom he married in 1944, just before shipping out to the Pacific theater to fight in World War II. I think that boat served as a reminder for him, of those things he experienced and learned in the Navy before becoming a professional land surveyor and family man. We all called him “Poppy”.
Poppy let me steer that boat as a kid. He taught me things about life, things like how to think as a captain thinks. He was sophisticated, also practical, and he shared his view of the world with me. I listened closely while we glided the wide open lake on clear nights. He’d quiz me on cardinal directions, and navigating by the stars. Out there on the water, I’d imagine orbits, the Earth turning with the Moon and Sun. Poppy would test me on finding Polaris for North or spotting the Big Dipper, telling the season by its shape.
He showed me the sky held secrets—morning reds predicting rain, cloud shapes forecasting weather.
The sky told us lots of things, if we knew what to look for. These interests, which he sparked in my imagination as a child, came to inspire a recent project to design a hiking trail for a city park. It is now known as “The Discovery Trail.”
The project’s goal was to build a ” Discovery Trail”, a one-mile hiking path through the Missouri woods and glades, offering an immersive experience with nature. The idea of a trail inspired by the changing seasons took root in my mind as a concept to explore when I realized the trail was a loop. Missouri’s distinct seasons hold profound significance, symbolizing the cyclical nature of change and comfort in the familiar holidays and ceremonies of our lives. If this was to be a nature trail, we could use the seasons as a metaphor for the attributes the trail would have. After the field survey of the property, I designed five zones along the trail, four representing each of the seasons and the final zone housing a celestial observatory within a beautiful stone labyrinth.
Land Surveying techniques were crucial to our success. It allowed us to create an entire plan from start to finish, locating the best trail design through the terrain and choosing the locations for our celestial observatory and other zones within the property boundary. Over the course of the year, we recorded the movement of the sun to establish the observatory’s alignment with celestial events, particularly marking three points of interest on the horizon; the Winter Solstice, the Spring/Fall Equinox, and the Summer Solstice.
I have always been intrigued by archaeological sites such as Stonehenge, the Pyramids in Egypt and Mesoamerica, Cahokia mounds, Chaco Canyon, and other ancient sites where earlier humans built the first calendars. By creating markers on the horizon, they were able to track year by year, season by season, the turning of the planets and stars, which was exactly what we would attempt to design and build at the city park.
The stone circle labyrinth was strategically laid out through surveying techniques, providing a vantage point from the central bench to witness the Earth’s motion around the Sun. As the Sun sets in the evening, it lines up to different horizon points along three cedar pillars. Each pillar top houses a prism to refract the rays of the Sun. Visitors who walk the labyrinth arrive on a wide, comfortable semi-circular bench, where they can relax and watch the turning of this natural calendar.
To accurately locate the Sun’s position in the sky on the solstices and equinoxes using land surveying techniques, we established a fixed reference point on the Earth’s surface. This vantage point must look out on an even horizon. This can be achieved by setting up a sturdy, stable base station with known coordinates using precise GPS measurements. We also used traditional terrestrial survey methods. We located every point with GPS, which allows us to draw the CAD design. Next, we performed an accurate theodolite (total station) instrument and measured the angles between the reference point and the Sun on the winter solstice sunset. The theodolite’s horizontal and vertical angles were carefully recorded, allowing for precise azimuth and altitude calculations of the Sun’s position. We also gathered elevation data with a level rod in order to determine the height of our pillars (+3 feet in ground).
This information was invaluable in constructing the observatory because construction was set to finish before the final readings of the Summer Solstice could be obtained. We fixed our reference point during a reading of the Winter Solstice sunset on December 21st, 2022. From that, and with the help of a local college physics professor, we figured the equation to find the angles to turn according to the latitude of Hillsboro, Missouri (Lat = 38.2197) for setting the other two pillars.
This is the equation:
Angle from Solstice to Equinox = arcsin(sin(23.44) / cos(Latitude))
Where: “arcsin” is the inverse sine function, “cos” is the cosine function
and “23.44” is the axial tilt of the Earth (approximately 23.44 degrees).
“Latitude” is the observer’s latitude in decimal degrees;
which in our case was 38.2197.
Let’s solve for it.
Angle to Equinox at Solstice = arcsin(sin(23.44) / cos(38.2197)
= arcsin( 0.3978/0.7856)
=arcsin (0.5064)
= 30.4220
≈ 30.42 decimal degrees
Now convert to Degrees Minutes Seconds = 30 degrees 25 minutes 12 seconds.
This is the angle we turned to set the other two pillars along an even radius from the center point.
This means that the sunset at the winter solstice will be about 30 degrees 25 minutes 12 seconds south of due west, and the sunset at the summer solstice will be about 30 degrees 25 minutes 12 seconds north of due west. After shooting the elevations we noticed there was a slight vertical angle from our reference point to the horizon. This put the pillars a bit to the south of due west to align with the solstice sunsets at this particular vantage point.
As mentioned, the contract for the finished construction was set for April, but we could depend on the mathematically figured angles to set the pillars correctly with the sunsets. I used the equation of angles to turn, drew it out in CAD, then went back out to stake it, including the location of each of the posts for the bench, which also align to these celestial positions. I also located the point for the “North Stone” and arranged the labyrinth walkways to fit exactly to these positions.
As a check, on March 21st, the Spring Equinox, we took another theodolite reading of the sunset (also noting the vertical height with a level rod) and sure enough, the sun was setting at the central Equinox point I had figured off of the winter solstice, so we knew we were on the right track. I held the points to set the pillars.
For construction purposes, I set two offset stakes 90 degrees on each side of each pillar, three feet from the center point. This was done to keep reference with measuring tape so that they would be on the perfect arc. When laying the concrete and setting the pillars the masons pulled off these points, and we checked level with Total Station from the center point. I also used a plumb bob with my eye all the way around them after while the concrete was setting. The pillars were carved out of the big cedar wood we had cleared, with fire etched calligraphy naming each pillar’s location.
As it turned out, the sunset on the Summer Solstice was directly in line with the northernmost pillar. On that day, my dad and I sat and observed with great anticipation and subsequent exhilaration.
Of course now this presents more scientific questions; Will the Sun set in a similar path next year?
This is why The Labyrinth deserves the title of an “Observatory”. Sure, in the modern world we have satellite GPS in our cars and the world is encircled in data. Scientists may see the minutiae of every velocity, weather pattern, and geoid position in real time from our computer screens. All of which is amazing. However, there is something very human and spiritual about seeing the motion from the vantage point of our local world, just like the humans before us. To watch the sky slowly turning and changing color in the cool of the evening, as the days get longer and the sun is gradually inching its way north is captivating.
Such wealth of knowledge remaining concealed within seemingly uncomplicated natural occurrences. We can just take a walk, and sit, watching the sun go down on another day on earth.
– Ryan Hurtgen
