4 Workshop on Chaco Archaeoastronomy & Living With Mystery

Introduction

This page provides a framework for an interactive workshop on the mysteries surrounding Chaco Canyon as an ancient astronomical site. The project arose out of Vera’s experience growing up in New Mexico, camping at the National Park, gazing at stars and petroglyphs, and never learning about their histories. While Vera grew up hearing that Chaco Canyon was a site where ancient inhabitants practiced astronomy, they found that there is much speculation and a lack of ethnographic evidence to support such a claim. At first, this was a frustrating discovery—Vera had been excited by the prospect of living near a site of ancient astronomy. However, the uncertainty surrounding Chaco Canyon can teach us a valuable lesson on being wary of confirmation bias and coexisting with mystery. The workshop below is heavily influenced by the “Conceptual Workshops” chapter of Jody Valentine’s Experimental Pedagogy (Valentine 2020).

Aims

Introduce participants to the discoveries that led to Chaco Canyon being thought of as an astronomical site, discuss confirmation bias, and consider the frustration and joy of mystery.

Part I: Chaco Canyon archaeoastronomy

Brief introduction to chaco canyon

Chaco Canyon is an archaeological site located in what is known today to be northwestern New Mexico. Between ~850 and 1250 A.D., the canyon served as a center for ancestral Puebloan people. Chaco is comprised of hundreds of house sites, some containing large kivas thought to be constructed for ceremonies. The house sites, together with a system of roads and waterways, formed one of the largest complexes in in the pre 19th-century United States.

TImeline of Archaeoastronomy

In 1964, Gerald Hawkins published a paper proposing that the rocks at Stonehenge were celestially aligned to create an astronomical “computer” to predict eclipses (Hawkins 1964). Archaeologists sought to find other sites in the world displaying similar celestial alignments. According to the National Park Service’s A Brief History of Chaco Culture National Historical Park, the study of archaeoastronomy at Chaco Canyon began when in 1971 Jonathon Raymon proposed that a “corner door at Pueblo Bonito marked the winter solstice.” In the same decade, Ray Williamson suggested that the kiva Casa Rinconada was astronomically aligned. At the summer solstice, sunlight was said to move across an opening in the wall of the kiva. However, the kiva had been reconstructed in the 1930s and it is unknown whether this phenomenon could have been visible previously.

In 1977, Anna Sofaer discovered slabs of rock placed such that sunlight hitting them within two weeks of the summer solstice would appear as a vertical wedge across a spiral petroglyph, and light hitting them on the winter solstice would frame the spiral. In her 1979 paper, Dr. Sofaer concluded that the dagger “shows the times of solstice and equinox in vividly symbolic imagery of light and shadow and provides solar (and lunar) information at other times in the year” (Sofaer, Zinser, & Sinclair 1979). The rocks have since shifted and display light patterns different to what Dr. Sofaer observed.

Supernova pictograph

The petroglyph in the images below may represent supernova SN 1054, which happened in 1054 AD. At this time, the ancestral Puebloan civilization thrived in Chaco Canyon. The supernova lit up the sky for two years and could be seen with the naked eye to the left of the moon.

Supernova Pictograph     Credit: Alex Marentes

Credit: Rob Pettengil

Discussion Questions

1. Why might people design structures to align with the solstices?
2. How do you think celestial alignments and the Supernova Pictograph should be portrayed to visitors at the site, given the uncertainty surrounding their histories?

Part ii: Confirmation bias

Confirmation bias is defined to be “the tendency to process information by looking for, or interpreting, information that is consistent with one’s existing beliefs” (Casad 2022).

1. Share a time you have encountered or been subject to confirmation bias in your life.
2. Why do you think confirmation bias exists?

Part iii: Bringing it together

1. Return to the supernova pictograph from Part I. If you did not know Chaco Canyon was studied as an astronomical site, what might you have seen in the image other than an exploding star?
2. SN 1006 was a supernova that happened 48 years before SN 1054 and shone even more brightly, but there is not evidence of any recording of the event in petroglyphs. What may have been special about SN 1054? What further information would you need to classify the “supernova pictograph” as a supernova rather than an instance of confirmation bias?
3. In truth, the intention behind alignments and petroglyphs at Chaco Canyon remains a mystery. There is a lack of ethnographic evidence for the site to be astronomically significant. As you contemplate the unanswerability of Chaco’s astronomy, what do you notice? Curiosity? A lack of closure?
4. Think about a mystery in your life. How do you engage with that mystery? Does it frustrate you? Do you treasure it?
5. How should archaeologists make conclusions about ancient sites without being able to time-travel?

References

Casad, B. J. (2022, October 6). confirmation bias. Encyclopedia Britannica. Retrieved from https://www.britannica.com/science/confirmation-bias

Hawkins, G. (1964). Stonehenge: A Neolithic Computer. Nature 202, 1258–1261. Retrieved from https://doi.org/10.1038/2021258a0

Sofaer, A., Zinser, V., & Sinclair, R. M. (1979). A Unique Solar Marking Construct. Science, 206(4416), 283–291. http://www.jstor.org/stable/1749388

Valentine, Jody (2020). Experimental Pedagogy. Retrieved from https://pressbooks.claremont.edu/experimentalpedagogy/