In the newest installment of Scott Thybony’s Canyon Commentary, he recounts a trip he took to Chaco Canyon National Historical Park in New Mexico with a team of scientists. Their destination was the top of a massive butte where ancient astronomers once observed the heavens using rock art carved into the stone. Scott and the team braved a rock climb and bone-chilling cold to record a lunar phenomenon that only happens once every two decades.
The smell of dust grew strong as the truck rattled along a washboarded road toward Chaco Canyon. Now on the edge of things, the ancient community had been the center of a dynamic region spreading throughout the Four Corners country a thousand years ago. Topping a rise I saw Fajada Butte in the distance, a solitary landmark under the winter sun.
On its summit the early Puebloans had carved a spiral petroglyph. And at summer solstice a thin wedge of light once descended through the outer rings to pierce the very center. The discovery of the Sun Dagger site by artist Anna Sofaer in 1977 overturned our thinking about prehistoric astronomy in the Southwest. The Solstice Project she founded later concluded the site also used light and shadow to mark the passage of the moon.
To further investigate this, Bill Stone from the National Geodetic Survey had received permission to spend a night on Fajada Butte. He planned to record the interaction of the full moon with the rock art during an astronomical event known as the major lunar standstill. Over a span of 18.6 years the location of the rising moon shifts along the horizon. Then it comes to an apparent standstill before repeating another progression much like a pendulum.
My job was to act as a Sherpa carrying cold weather gear, a pile of climbing equipment, and a bigger pile of cameras, tripods, and surveying instruments. Scott Sholes, an experienced climber, would do the same.
After parking the truck, the three of us began hauling packs to the foot of the ascent route. With everything ready, Sholes led the climb up a 45-foot cliff to where a heavy mesh screen blocked our way. To protect the site the park service had placed a locked hatchway at the crux of the climb. With his bare fingers beginning to numb, Sholes worked fast to open it.
We took turns carrying full packs, staying clipped into a cable for safety. It was quicker than hauling the gear up by rope. All went smoothly, and after three climbs we had everything on top. Near the summit we made a base camp where Bill unpacked a theodolite for horizon measurements and set up a survey-grade GPS unit to run overnight for greater accuracy.
At the Sun Dagger site three sandstone slabs stood upright next to the cliff. Behind them the Chacoans had pecked a spiral about 16 inches in diameter. At certain times of the year sunlight passed through a slit between the slabs and hit the petroglyph. In 1989, the rocks shifted after being undercut by erosion which prevented light from hitting the spiral at summer solstice. The park service closed the Sun Dagger site to prevent further deterioration.
A bitter cold arrived at nightfall as Bill set up five cameras to record the shadow effects of the moonrise. I threw on my last layer knowing it had reached 12 degrees below zero the night before. Soon the moon broke through a band of clouds and threw a shadow across the spiral petroglyph dividing it in two. In the numinous moonlight the moment was as solemn as entering a sanctuary. On top of Fajada Butte the ancient skywatchers had been dealing with the big questions. The tracking of the sun and moon reflected their connection to the wider cosmos and a relationship to the hidden forces shaping their lives.
We soon turned in, and I crawled inside a bivy sack as the cold settled bone deep. Next morning we finished our observations by watching a ragged shaft of sunlight pass through the spiral. We returned to the visitor center a park ranger looked up. Sounding a bit surprised he said, “You survived!”
