Peñasco Blanco: Observatory

During our visit to Chaco Canyon, we hiked 3-1/2 miles from Pueblo Bonito to Peñasco Blanco, sitting atop the bluff some 300-400 feet above the canyon basin. I had wondered why these villages were sited in such disparate places. Why was Peñasco on top the bluff and Bonito at the base of the cliffs? It wasn’t until I returned to Las Cruces and had time to stick my nose in my reference books that I got an answer. Peñasco was an observatory – of sorts.

Astronomy was important to the Chacoans and many of the pueblos are precisely aligned to some aspect to the solar cycle or the lunar cycle. Astronomy apparently had a major influence on customs, rituals, and ceremonies.

Peñasco Blanco, Spanish for white bluff, is called by the Navajo “tableland tapering to a point house,” an apt description of the great house sited above the confluence of Chaco Wash and Escavada Wash.

That, however, does not tell the story. Peñasco is in perfect alignment with Pueblo Bonito and Una Vida, along a straight line eight miles long. All three were built in the mid to late 800s.

What truly makes Peñasco unique is its alignment to what astronomer’s call the lunar major standstill. I’ve tried to find out what that means, and it gets complicated quickly. The moon does not orbit the earth in the same plane as the earth orbits the sun, a plane called the ecliptic. If it did, we’d have an eclipse every two weeks. Instead, the moon’s orbit is tilted about five degrees above the ecliptic.

The lunar cycle from one major standstill to another is 18.6 years and the cycle was first measured and explained by Hipparchus, the Greek astronomer who lived from 190 to 120 BC, so there’s nothing new about it. It all has to do with very complex celestial mechanics that govern the orbit of one body around another [moon and earth] while under the influence of a third body [the sun].

Here’s the technical definition ... “As the earth travels its annual orbit around the sun, with its rotational axis tilted at about 23.5° from the vertical, the sun’s declination changes from + 23.5° at the summer solstice to -23.5° at the winter solstice. Thus, in the northern hemisphere, the sun is higher in the sky and visible for a longer period of time in June than it is in December. It’s why we have seasons.

“Unlike the sun, the maximum and minimum declination reached by the moon varies. This is because the plane of the moon’s orbit around the earth is inclined those five degrees to the plane of the earth’s orbit around the sun, and the direction of this inclination gradually changes over the 18.6-year cycle, alternately working with and against the 23.5° tilt of the earth’s axis.” [Source:Wikipedia]

At the standstill, the moon appears to stand still in the sky for a brief period before changing directions and moving oppositely, either north or south.

Keep in mind this has nothing to do with the phases of the moon. It just means, if you stand facing the north star, how far to the south of it is the moon at its zenith. Sometimes, at an equinox, it appears farther north than you might expect it to be. Other times it’s farther south, just like where the sun peeks over the Organ Mountains in June and December.

I’ve taken time to mention this because we have loads of instruments to measure precise angles and times and computers to do calculations to however many decimal places we desire. The Chacoans had none of this, and yet their calculations were just as precise. It’s built into the architecture of Peñasco Blanco and Pueblo Bonito. Anna Sofaer, director of the Solstice Project Survey [in Kendrick Frazier’s book, People of Chaco] said, “It suggests the Chacoans may have favored these particular angles (lunar standstill) in order to incorporate a geometry of the sun and moon in the internal organization of the buildings.” An illustration in Frazier’s book refers to “inter-building bearings” that correlate to the orientation of individual buildings to the cardinal directions and to the lunar major and minor standstills. There are walls in perfect alignment not only with the cardinal directions and standstill angles but also with other walls in other pueblos. How Chacoans achieved such precision is unknown but marvelous to contemplate.

Observant Chacoan holy men, whom Park Rangers referred to as Sunwatchers, would have noticed the relationship between eclipses of the moon and its standstill cycle. They perhaps used their observations to establish precise dates for major festivals and ceremonials, so vital to the sacred rituals of the society.

What binds a society, then and now, are adherence by individuals to a community-accepted body of behavior and beliefs. We often hear people talk about the decay of our society. What actually does that mean, except individuals no longer choose to conform? It puts the society in flux until a new belief system emerges to unify the community.

Archeologists assume Chacoans used solar and lunar cycles to reinforce societal behavior. For instance, we were told during the full-moon lecture at Pueblo Bonito, at the solstice, the date was set for a ceremonial during which people recommitted to the community, “to do good.” If they failed to hold the ceremony and the people had been “bad,” the sun would continue south and the earth would die. The recommitment assured the sun of the people’s devotion to each other and the world, and it began its return.

What was practiced at Peñasco Blanco was ancient when the great house was new. We were assured by the Ranger, it is still part of today’s puebloan ceremonials, so sacred it cannot be talked about publicly less it offend the sun and it continues south on its journey through time.

Posted by Bur Russo