I first heard the term “archaeoastronomy” in a college course a few years ago. I’d gone back to school to study ecology and environmental issues and one of my professors worked as an archaeologist in the jungles of South America uncovering Mayan temples. He noted that many ancient cultures throughout the Americas built structures that were intended to chart the course of the stars, the sun, and the moon. I thought that was pretty cool.

When I drove down the road to Chaco, I landed right in the middle of one of the largest and most precise archaeoastronomy destinations in North America. But I didn’t really know that until I attended a fabulous lecture on a Saturday evening during my visit to the park. That evening, after dark, I headed to the Chaco planetarium to join one of the most seasoned park rangers, and an astronomy nut, to learn all about astronomical clues scattered throughout Chaco Canyon.

As I walked to the planetarium, the night sky spread out a blanket of stars across the horizon. I leaned my head back as far as it would go and took in the view. No street lights blazed down the streets here, or anywhere for miles around. It was very, very dark, making it possible to clearly see the brilliant rope of our Milky Way galaxy stretching all the way across the sky.

I sat down next to many of the other campers and ranger GB Cornucopia stepped up to the front. He flipped on a projector that showed a time lapse movie of stars racing across Fajada Butte.

Fajada Butte Chaco Canyon

I’d spent the past two days constantly driving past Fajada Butte. I’d spent a few hours photographing it under different lighting conditions. But I totally missed one of the coolest things about it: the ramp leading up from the canyon floor to the top of the butte. Look at the photo above. Do you see the ramp?

What about now?

The ramp, on the lower right part of this view of the butte, was over 750 feet long an rose over 300 feet over the valley floor, leading almost to the top of this massive geologic structure. It was a huge feat of engineering according to the High Altitude Observatory webpage:

The ramp, 230 meters long and rising almost 100 meters above the valley floor, was apparently constructed in three sections. The first followed an erosional ridge to the first prominent cliff band on the butte. The second was a heavy masonry structure that extended from the top of the first cliff band to the second cliff band, along which ruins of numerous small cliff dwellings are to be found. The final part of the ramp was likely a combination of carved steps and scaffolding structures. Even by Chacoan standards, this represents a construction project of a significant magnitude, and suggests that the butte might have played an important ceremonial role at Chaco.

Wow! Why would the people of Chaco do that? Well, there’s something very interesting at the top of the butte. Three flat, skinny rocks are perched on the side of a flat rock. On the flat rock, hidden from the sky by the three rocks, is a spiral petroglyph. Well, so what? It turns out that this petroglyph is an extremely accurate calendar that marks high noon of the summer and winter solstices (or it was until lots of hikers wore down the dirt on the butte, caused the rocks to shift, and messed up the calendar). What happens is light filters through the slabs of rock, slowly creating a sword of light that on the summer solstice bisects the center of the spiral pictograph. On the winter solstice, two slim daggers of light appear appear on either side of the pictograph like tiny bright bookends.

Chaco Sun Dagger

Here’s a neat little illustration I found on Ms. Lopez’s webpage that shows how the fabulous calendar works.

Sun Dagger at Chaco Canyon

Evidently, the ramp on the side of the butte was built so that it would be easy for the people of Chaco to climb up the butte and watch the calendar. I wonder if ceremonials paraded up the ramp on the solstices. I can imagine long lines of people, decked out in features, traveling this narrow path to witness the longest day of the year, or to ensure that the shortest day of the year would morph into longer days and the season of rebirth.

This is only one of the huge number of astronomical alignments all over the park. Casa Rinconada, the largest kiva in the park, has some very intriguing directional alignments:

Casa Rinconada has a main axis which is aligned to true cardinality along a north south line passing through the centres of the north and south doorways. This north south axis has an azimuth of 359°56′. If you connect each wall regular wall niche to the one opposite it, you will find that all but one of them pass within 10 cm of the kiva centre, meaning that the kiva is a model of a perfect circle. One of these lines has an azimuth of 89°52′ and establishes an east west line. According to archaeoastronomer E. C Krupp, these features are tied to the order of space and the direction of time.

Case Rinconada, Chaco Canyon
In addition, on the summer solstice, a beam of light passes through the only window on the east wall and nicely illuminates two niches on the far wall. Perhaps that didn’t happen long ago when the Chaco people had built a ceiling on the giant kiva, but I like to think that this structure did also serve as a calendar for those who couldn’t make the trip all the way up Fajada Butte. Here’s a video with the awesome Chaco park ranger G.B. Cornucopia explaining the astronomical alignments at Case Rinconada.

There are so many more things all around Chaco that are tied to the movement of the sun, the appearance of the stars, the movement of the moon, and the cardinal directions. The Chacoans built great roads throughout the region running due north, or in perfectly straight lines radiating out from great houses. When the roads encountered an obstacle, like a cliff, the road builders didn’t deviate from their course, they simply carved steps up cliffs. I’m still learning about all of the ways these people constructed their world to be in alignment with the cosmos. They were so much more skilled at understanding astronomy that most people in today’s world, and that in itself was a huge accomplishment.

Here’s a final video of the awesome Carl Sagan talking about astronomy at Chaco.


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