Ch.5: Regional System

URBAN GENESIS AT CHACO: Case Study of the Origin of Civilizations. Chapters: 1 2 3 4 5 6

5.6 Celestial Alignments and Relationships at Chaco

Figure 4.26a shows the winter and summer solstices in relation to the canyon. The winter solstice rise and summer solstice set almost align with the visual axis of the canyon from Pe?asco Blanco across Pueblo Bonito to Kin Nahasbas. However, even a two-degree deviation between the visual axis and the solstice positions would have been noticeable, as shown in the diagram. I am therefore reluctant to conclude that solstice alignments explain the exact positioning of these structures, although the two axes may have been considered associated. However one obvious phenomenon is that, in midwinter, the rising solstice sun would shine straight up the length of the canyon, and the summer solstice sun would shine straight down it at sunset. In addition to being a simple natural calendar, this coincidence may have caused Chacoans to associate 'canyon east' with midwinter, and 'canyon west' with midsummer.

Figure 4.26b. This description is based directly on Sofaer, Sinclair and Donohue, "Solar and Lunar Orientations of the Major Architecture of the Chaco Culture of New Mexico" (1990). Anna Sofaer (1979) demonstrated conclusively that the Chacoans were able to determine the solstices, equinoxes, and the Maximums and Minimums of the 18-year lunar precessional cycle, which is explained below. Sofaer first demonstrated Chacoan celestial knowledge at the 'observatory' located near the top of Fajada Butte, where three stone slabs were arranged to cast patterns of light and shadow against two petroglyphs that were pecked into the rock face behind the slabs. She has since argued that solar and lunar alignments were used in great-house design both to orient the structures and to guide the arrangement of their internal geometry.

Careful observation will reveal that the moon not only rises later each day, but that it also rises at a different point on the horizon each day. During the moon's 28-day orbit, it appears to swing regularly north and south, because its orbit is inclined to the Earth's axis of rotation. In addition, the degree of inclination of the moon's orbit varies, so that the magnitude of the north-south swing of the moon also varies over the years. When the Lunar orbital inclination is at its greatest, moonrises and sets will swing farther to the north and south. This orbital inclination varies as a sine function so that the 'maximum monthly swing' persists for some time before the degree of variation begins to decrease noticeably. This period in the precessional cycle is called the Lunar Maximum Standstill. Nine years later, the moon will cycle through Minimum Standstill for the same reasons.

At Lunar Maximum Standstill, the north-south variation of moonrises and -sets exceeds the deviation of the canyon itself. During the years preceding and following the Lunar Maximum Standstill, the extreme north-south variations would match the canyon axis precisely. Furthermore, at Maximum Standstill the southernmost setting of the moon aligns with the southeast edge of West Mesa, and almost shines straight into the center of the canyon between Pueblo Bonito and Chetro Ketl. No alignments of buildings match this angle, but the relationship of the Maximum Standstill to the canyon would make this slow change in the magnitude of variation apparent to a long-time resident of the canyon.

The Lunar Minor Standstill does seem to have been used as the basis for great-house orientation. Within the canyon, the back wall of Chetro Ketl aligns with the northernmost moonrise at Minimum Standstill. This is also true of two of the four major outliers: Salmon ruin and Pueblo Pintado. Pueblo del Arroyo, meanwhile, faces the southernmost rise directly--meaning that the back wall of the great-house is perpendicular to the moonrise. The longitudinal axis of Kin Kletso, just east of Pueblo del Arroyo, is also aligned with the southernmost rise at Minimum Standstill.

Use of celestial alignments in great-house design strongly indicates a cosmological significance of these structures. If different great-houses were built by different societies or institutions, perhaps those institutions affiliate themselves with different celestial events, and therefore with different times. The great-house builders may have waited for an auspicious moment in which to begin a major building campaign, thereby justifying the high cost of the construction project. If so, the lunar event is used to interrupt or differentiate auspicious time from regular time much in the way that Eliade describes the process by which space is differentiated into the sacred and the profane (1957). Furthermore, by starting a structure during a sacred moment, the structure would be permanently associated with that moment in time as well as in space. The periodic return of the Lunar Minimum Standstill may have been used as a reaffirmation of the cosmological position of the great-house.