The Chacoans Main Hobby

The first archaeoastronomical investigations in Chaco Canyon took place in the 1970s (Williamson et al. 1975 1977) with the analysis of the large kiva (20 meters in diameter) known as Casa Rinconada. It is a building constructed with meticulous care; for example, it has an axis of symmetry, defined by two opposing T-shaped accesses, directed precisely northward. Little windows have been carved into the inside wall; their arrangement is so regular that a line joining two opposite windows passes through the center of the circle with a maximum error of 10 centimeters. Four holes in the wall,

Chaco Canyon Astronomical Alignments
Figure 7.2: Possible astronomical orientations of buildings in Chaco canyon (adapted from Sofaer 1997, under kind permission)

possibly for posts supporting the roof, form a perfectly centered square, but oriented 30 degrees north of east. During the summer solstice the sun's first rays strike the windows and then move along the walls until they light up a specially placed niche. The deliberateness of such an alignment has been contested by some scholars on the grounds that the northwest post would have cast a shadow over the niche. I would argue that we do not know what the post looked like (or if it actually existed), but it is not that important. To have more incontrovertible proof of Anasazi astronomy, we simply need to look at a different building (Sofaer 1997).

There are 14 buildings at Chaco, of which 12 appear to be astronomically oriented: Three are oriented on the cardinal points (Pueblo Bonito, Pueblo Alto, and Tsin Kletzin), of which Pueblo Bonito, the largest building, is oriented with great accuracy; the wall that divides the half-circle is oriented within 15' of true north, and the western half of the south wall runs straight on the east-west line within 8' (Malville and Putnam 1993) (Plate 14). A fourth building is oriented toward the summer solstice (Aztec Ruin). Five buildings are oriented toward the north minor lunar standstill (Chetro Ketl, Kin Kletso, Pueblo del Arroyo, Pueblo Pintado, and Salmon Ruin), and two buildings are oriented to the north minor lunar standstill (Penasco Blanco and Una Vida).

Evidence of the Chacoans' interest in lunar and solar cycles is further seen throughout Fajada Butte, a 135-meter-high rocky peak 7 kilometers southwest of Pueblo Bonito. There are numerous petroglyphs, that is, drawings carved onto rocks. One is a few meters from the top; it is a semicircle crossed by a radial line perpendicular to the diameter of the base, with a circle placed to the left of the line itself. Thus it is a stylized plan of the Pueblo Bonito complex, which has a large kiva set to the left of the dividing wall. An arrow is drawn outside the figure of the semicircle. We do not know what the carver of the petroglyph had in mind, but the figure links the Pueblo Bonito building with a symbolism relating to the Sun.

Apart from symbolic petroglyphs, on Fajada Butte there are also carvings used as lunar-solar calendars (Sofaer et al. 1979, 1982, 1989). The most interesting, although controversial, example is the so-called petroglyph of three slabs, placed in the vicinity of the summit. This is a drawing made up of two spiral figures; three great slabs of stone are propped on the same rock, over 2 meters high and weighing about a ton each. They cast a shadow over the whole surface on which the drawing is traced. The light can illuminate the figures only through the two openings between the three slabs; the passing of the "blades" of light thus created will vary day by day. At the summer solstice the blade of light crosses the center of the largest spiral. On subsequent days the "arrow" shifts to the right and a second "arrow" appears to its left. At the equinox this second blade of light reaches the center of the smallest spiral. The movement of both proceeds to the right to the point of illuminating tangentially the largest spiral at the winter solstice. By

WSNTER SOLSTICE

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EQUINO* OR MID-POSITION OF THE SOLAfVLUNAP CYCLES

SUMMER SOLSTICE

Solar markings at midday

WSNTER SOLSTICE

0"

EQUINO* OR MID-POSITION OF THE SOLAfVLUNAP CYCLES

SUMMER SOLSTICE

Solar markings at midday

Solar/lunar markings at rising

Figure 7.3: Solar and lunar markings on the 3-slabs petroglipys (adapted from Sofaer and Sinclair 1982, under kind permission)

continuing to observe the effects of light and shadow throughout the year, researchers realized that when the sun had, at dawn, an azimuth close to that of the moon as it reaches the north minor standstill, the large spiral was half lit. In other words, when the sun simulates the north minor lunar standstill, the petroglyph is illuminated in a special way. This observation encouraged researchers to simulate with artificial light the major lunar standstill as well (which, as we know, cannot be reached by the sun, and is reached by the moon only once every 18.6 years; see Appendix 1). Perhaps it will come as no surprise then to learn that in this case the light leaves the spiral figure in the dark, just grazing it, that is, passing tangentially.

It is difficult to believe that such light and shadow effects could occur by chance (although the risk of "data selection" is always present in these studies). The three-slab petroglyph appears therefore to be a clever lunar-solar calendar; the most puzzling thing about this site is the sheer tenacity of the astronomers who built it, who were forced to make meticulous observations of the sun and moon for many years, climbing up and down the peak of Fajada Butte, if not every day then certainly frequently.

Petroglyphs are not unique to Fajada Butte, but can be found to some extent all over the canyon. One of the most famous drawings is on a rocky outcrop northeast of Penasco Blanco. It shows a lunar crescent, a shining

Solar/lunar markings at rising

Figure 7.3: Solar and lunar markings on the 3-slabs petroglipys (adapted from Sofaer and Sinclair 1982, under kind permission)

MAJOR STANDSTILL OF THE MOON

EQUINOX OP Win-POSITION MINOR STANDSTILL OF THE SOLAFVLUNAfl CYCtES OF THE MOON

MAJOR STANDSTILL OF THE MOON

star, and a hand. To understand its possible significance, let's take a trip to the China of the eleventh century.

On July 4, 1054 AD, Yang Wei-te, royal astronomer to the Chinese Court, was engaged in his habitual observations when he suddenly realized that there was a new star (a "guest" star, to use his words) in the sky, in the constellation of Taurus. The star shone so brightly (from four to ten times more brilliantly than Venus, according to modern calculations) that it was visible during the daylight for 23 days; nighttime visibility lasted for about 2 years. Observations of this object are reported also in other Chinese and Japanese sources, although curiously there is no evidence that the phenomenon was ever recorded by Europeans or Arabs. Physically, this was a case of the explosion of a supernova—a star that has exhausted its nuclear fuel and undergoes a violent contraction process, culminating in an explosion. What is left is an object that is extremely dense and invisible to the naked eye, typically what we call a neutron star, surrounded by a nebula (in the case of the phenomenon observed in 1054 AD, we are talking about the formation of what today is called Crab Nebula).

On July 4, 1054 AD, in Chaco Canyon, the moon was entering its final quarter and at dawn it was located less than three degrees from the supernova, facing the same position as indicated by the petroglyph, so that it is tempting to interpret it as a depiction of this phenomenon. Unfortunately, it is impossible to date petroglyphs, so we shall never be sure whether the drawing was made on that particular day, with the aim of representing the appearance of what might be interpreted as a second sun (of course, it may be that the petroglyph simply represented a combination of the moon and Venus). Nevertheless, there exist ceramics originating in New Mexico, definitively dated at 1050 to 1070 AD, on which very similar depictions appear (Brandt et al. 1977).

Orientations of single buildings and petroglyphs show clearly the meticulous interest of the Chacoans in the celestial cycles, and we are therefore tempted to interpret Chaco as another of those places where an elite of priests-astronomers exerted their power. A further hint in this direction comes from the suggestion that the ceremonial center of Chaco might have been constructed according to a global plan. Indeed, if one looks at the layout of the buildings in Chaco Canyon, one wonders why they have been constructed so far apart from each other. There do not seem to be any geological—the type of terrain, for example—or agricultural reasons, nor any considerations relating to water sources. (It is not even clear why so many buildings were erected there.) Thus it is likely that the layout of the complex was conceived in terms of an overall scheme. The first to propose the existence of such a master plan was Fritz (1978), who noticed that Pueblo

Alto and Tsin Kletzin, in a north-south direction, and Pueblo Bonito and Chetro Ketl, in an east-west direction, form a cross; that is, the ideal line joining the first two cuts in half perpendicularly the line joining the other two. It was later proposed that most of the Chaco buildings are astronomically related to each other; for instance, the two moon-oriented buildings that lie many kilometers from the Canyon, Pueblo Pintado (27 km) and Kin Bineola (18 km), are correlated with moon-oriented bearings with buildings in the center of the Canyon (Chetro Ketl, Pueblo del Arroyo, and Kin Kletso).

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