prehistoric-southwest

Credits

kolinski — Thu, 27 Jan 2022 19:40:51 +0000

Credits kolinski Thu, 01/27/2022 - 12:40

This slide set was made possible through the help of numerous people. Kim Malville (University of Colorado at Boulder) was generous beyond the call of duty in providing reprints and preprints of recent and/or hard to find papers, and in providing us photographic and video material, as well as answering our barrage of questions. Michael Zeilik (University of New Mexico in Albuquerque) provided constructive criticism on an early draft of the text, as well as numerous reprints and preprints. Florence Lister also provided useful suggestions. Mrs. Marcia Logsdon kindly granted us permission to make use of some of her husband's beautiful aerial photographs. We also benefited from the computer graphics expertise of Don Middleton and Tim Scheitlin (SCD/NCAR). Finally, PC and ORW wish to thank Chaco Culture Park superintendant Butch Wilson for granting us permission to accompany the 1997 summer solstice monitoring team to the 3-slab site, and Park rangers G.B. Cornucopia and Gary Henson for their pleasant company throughout a most enjoyable day on Fajada butte. Wendy Hawkins transposed pages to DRUPAL in November 2018 and updated some information. The High Altitude Observatory is a division of the National Center for Atmospheric Research, which is sponsored by the National Science Foundation.

Southwest Aerial Map: Map by Tom Bogdan; top right and bottom left photographs by Paul Charbonneau; top left aerial photograph by Paul Logsdon, copyrighted, and used by permission; bottom right photograph courtesy of Kim Malville, Astrophysical and Planetary Sciences department, University of Colorado at Boulder.
The Seasons: Digital imaging by Don Middleton, Scientific Computing Division, NCAR.
Hovenweep Castle: Photograph by Dick White.
Solstice Window, Solar Symbol Petroglyph, Fajada Butte, 3-Slab Slit, Sun Dagger, Cliff Palace, Lunar Astronomy, and Solar Astronomy: Photographs by Paul Charbonneau.
Hopi Tawa Kátsina: Photograph by Curt Zukosky, NCAR.
Solstice Marker: Images digitized from the video The Hovenweep Sun Dagger.
The Sun Temple: Floor plan redrawn from chapter 8 of J. McKim Malville's Prehistoric Astronomy in the Southwest. Slide set produced April 1999. Copyright HAO/NCAR 1999-2004.

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Supernova Pictograph

kolinski — Wed, 26 Jan 2022 22:50:20 +0000

Supernova Pictograph kolinski Wed, 01/26/2022 - 15:50

A pictograph, associated with the Ancestral Puebloan culture found in Chaco Canyon, may depict a supernova that was first observed on July 4, 1054 A.D. The remnant of this supernova, which consists of debris ejected during the explosion, is known as the Crab Nebula and is located in the constellation Taurus. The supernova was visible in broad daylight, having reached a maximum brightness about ten times that of Venus, the brightest astronomical object visible from Earth besides the Sun and Moon. It remained visible by day for 23 days, and by night for 653 days. Observational accounts of this spectacular phenomenon have been found in both Chinese and Japanese records. Curiously, only two brief reports are known from medieval Europe.

Supernova pictograph panel contains three symbols: a large star (supernova), a crescent moon, and a hand print.

The pictograph was painted on a horizontal overhang six meters off the ground, located on an East-facing cliff face five hundred meters Northeast of the ruin Peñnasco Blanco. Strong circumstantial evidence points to the pictograph being a depiction of the supernova. The crescent is the moon, the star shape to the left the supernova, and a life-size hand print is taken to indicate that the site is sacred. Calculations of the Moon's orbit back to July 5, 1054 have shown that the moon was waning, just entering first quarter. These calculations also indicate that at dawn on July 5, 1054 in the American Southwest, the moon was within 3 degrees of the supernova, and its crescent oriented as on the pictograph (provided the pictograph is viewed looking up with one's back to the cliff, as the authors of the pictograph most likely did). With the apparent width of the moon being about half a degree, this pictograph comes basically as close as it possibly could to being a true scale rendition of the 1054 supernova seen in conjunction with the waning moon.

On the nearly vertical cliff face below the supernova a Sun-symbol can be seen, painted in pale yellow over a much faded red background. This, combined with a clear view on the mesa top to an eastern horizon suitable for calendrical purposes, might well indicate that the site was also a solar-observing station. From there, the Peñasco Blanco Sun-priest perhaps first noticed the supernova prior to a sunrise observation. Given how rare such an event must have been, it is then conceivable that he might have wanted to record the event. Over a dozen other examples of rock art possibly representing supernova 1054 (i.e., bright "star" close to a crescent Moon) can be found throughout the Southwest, but few are as astronomically convincing as this pictograph.

Very few probable non-solar astronomical records are found in the rock art of Chaco Canyon. This is somewhat peculiar, because the eleventh century, during which the Chaco Phenomenon reached its peak, saw quite a few unusual astronomical events: the 1054 supernova, the 1066 passage of Halley's comet, starting around 1077 numerous large sunspots visible to the naked-eye (reported in Chinese records), as well as the total solar eclipse mentioned previously (July 11, 1097). It then becomes tempting to look for other possible records of unusual astronomical phenomena. Scrutiny of the Sun-symbol reveals that the faded red pigment over which the symbol is painted extends to the right, in a manner that to the modern and astronomically inclined eye is suggestive of a comet tail. Could this be a record of Halley's comet? It is certainly a plausible hypothesis; but as with most astronomical sites and devices described in this slide set, it is likely to remain a conjecture.

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Lunar Astronomy

kolinski — Wed, 26 Jan 2022 22:39:32 +0000

Lunar Astronomy kolinski Wed, 01/26/2022 - 15:39

Figure 1. Two peculiar pictographs painted in red may represent a record of lunar observations.

Figure 1 shows a view looking straight up the inside of the square tower at Cliff Palace, Mesa Verde, from ground level. Notice the two peculiar pictographs painted in red on the wall of the third story room in the tower. There is good circumstantial evidence that these two pictographs represent a record of lunar observations.

Next to the Sun, the Moon is perhaps the most conspicuous astronomical object in the sky, because of the sequence of illumination phases it undergoes every 28 days. Because the Moon's orbital axis about the Earth is nearly parallel to the Earth's orbital axis about the Sun, the Moon follows daily and seasonal paths in the sky that resemble the Sun's. However, because of the approximately 5^o difference between the two orbital planes, the azimuth of moon rise (or moon set) can oscillate by up to ± 6^o 40' (for an observer at 36^o latitude) about the Sun's rising (or setting) azimuth in the course of a monthly lunar cycle. In addition, the Sun's gravitational pull leads to a procession of the Moon's orbital axis, with a period of 18.6 years. This means that every 18.6 years, the rising or setting Moon reaches a northern extreme in rising and setting azimuth at summer solstice, and a southern extreme at winter solstice. These are called major standstills. While such standstills can in principle be determined using horizon observations, as with the summer solstice Sun the Moon's year-to-year angular displacement along the horizon at summer solstice is very small near standstill. Unlike for the Sun, anticipatory observations must now be carried a few years ahead of the major standstill.

Figure 2. Pictographs on the third story of the square tower at Cliff Palace. The left panel, located on the inside North wall, can be interpreted as a "teaching aid" demonstrating the back-and-forth motion of the rising and setting Moon along the horizon, in the course of one year. The panel on the right is located on the west wall next to the small square third story window, and can be interpreted as a tally of years between major lunar standstills.

Redrawn from diagrams in chapter 8 of J. McKim Malville's "Prehistoric Astronomy in the Southwest"

From the square tower's small third story window noted in the preceding slide, a line pointing to the moon set azimuth of the (southern) major lunar standstill passes through the narrow gap between the two large towers of the Sun Temple. It has been suggested that this is an intentional construct aimed at marking major lunar standstills. Further support for this hypothesis comes from the two aforementioned pictographs, reproduced in figure 2. The first (on the left) can be interpreted as a space-time diagram of the moon set's daily displacement along the horizon: azimuth runs horizontally and time vertically upward, and the zigzag lines depict the back-and-forth motion of the moon along the horizon, for the rising (left half of diagram) and setting (right half) Moon. Note that there are a total of twelve zigzags depicted in each half of the diagram, which come as close to adding up to a year as it could, given that the year and lunar month are not commensurate.

Of course, different interpretations of these pictographs are possible, especially since zig-zag patterns and rows of tick marks are common in Anasazi rock art. Other possible evidence for the Anasazi's lunar interests can be found at nearby Chimney Rock, where, as seen from the mesa-top pueblo, moon rise at major standstills is neatly framed by the twin rock towers giving the site its name (see slide 1, The Ancient People). It has been also suggested that the 3-slab slit site on Fajada butte could have also served as a marker of major lunar standstills, based on the way in which the side edge of the outer slab casts a shadow across the spiral petroglyph. Once again the lunar-cycle interpretations of these sites represent only plausible conjectures. A significant counterargument comes from the lunar astronomical practices of modern Pueblo people, who show great interest in the phases of the moon for time-keeping and yearly calendrical purposes, but not in its longer orbital or calendrical cycles.

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Cliff Palace

kolinski — Wed, 26 Jan 2022 22:28:39 +0000

Cliff Palace kolinski Wed, 01/26/2022 - 15:28

Cliff Palace, at Mesa Verde National Park.

Cliff Palace, at Mesa Verde National Park is the largest cliff dwelling at Mesa Verde, with 217 rooms, 23 kivas and an estimated resident population of 200–250. The prominent square tower seen in this photograph is the tallest structure at Cliff Palace. Notice, and make a mental note of, the small third story window slightly above the shadow line.

A possible Sun-watching station has been identified at the South end of Cliff Palace. From this location the southwestern horizon is featureless, except for the Sun Temple standing some 300 meters away on the mesa top across Cliff Canyon. At winter solstice, seen from the observing station the setting Sun touches the horizon between the Sun Temple's two main towers. It has also been suggested that the smallest tower in the Temple's West end might have served as an horizon marker to anticipate the winter solstice by some 20 days. These solar alignments inferences—and other alignments of a different nature discussed along with the next slide—only hold provided that the circular rooms of the Sun Temple were indeed towers that extended by a significant height above the Temple's outer enclosing walls; in the present-day ruin they do not. Whether they ever did (or were intended to) is likely to remain a mystery.

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The Sun Temple

kolinski — Wed, 26 Jan 2022 22:22:31 +0000

The Sun Temple kolinski Wed, 01/26/2022 - 15:22

The Sun Temple, in Mesa Verde National Park.

The Sun Temple is located in Mesa Verde National Park. It is perhaps the most enigmatic of extant Puebloan buildings. The name was originally coined in view of the peculiar Sun-like design located on a boulder on the Southwest corner of the ruin. Its construction began in 1275, well after the Mesa Verde inhabitants had moved from the mesa top into their spectacular cliff dwellings. Based on the quantity of rubble removed during excavation, it is estimated that the walls of the Sun Temple stood 4 to 5 meters high. However, the lack of roofing timber in the ruin indicates that the building was never completed. It appears that construction simply stopped in 1276, when the Mesa Verdeans suddenly abandoned the area.

The bottom diagram in the image is a schematic floor plan of the building. The main part of the building is D-shaped, and consists of a windowless double wall enclosing two circular tower-like rooms, in a very symmetrical manner. The West "annex" of the building contains many small rectangular rooms as well as two small circular rooms. Built on the mesa top at the confluence of Cliff and Fewkes Canyon, the Sun Temple stands at the heart of the Mesa Verde cliff dwellings, and was probably meant to serve as a ceremonial center for the surrounding population, estimated to number at least 600 in the thirteenth century. If so, it would represent the largest ceremonial structure ever built by the Anasazi. Whether the ceremonies taking place in the Sun Temple (if any) had anything to do with the Sun will remain forever unknown.

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Solar Eclipse Petroglyph

kolinski — Wed, 26 Jan 2022 20:30:11 +0000

Solar Eclipse Petroglyph kolinski Wed, 01/26/2022 - 13:30

A petroglyph, suggestive of a solar eclipse, is found on the South side of a large boulder near the Una Vida ruin in Chaco Canyon.

The rock art interpretation problem can become acute when considering possible direct depictions of astronomical events. One can certainly argue that to a culture preoccupied with solar observations for crucial calendrical and ceremonial purposes, rare events such as solar eclipses must have been quite impressive, perhaps to the point of being worth recording in some form. There were actually four total solar eclipses visible from somewhere in the San Juan basin between A.D. 700 and 1300: 13 April 804, 11 July 1097, 13 June 1257, and 17 October 1259 (solar eclipses also occurred on 29 July 957 and 7 March 1076, but were only partial in most of the San Juan basin). This slide shows a suggestive petroglyph, which is found on the South side of a large boulder near the Una Vida ruin in Chaco Canyon. This boulder appears to have been an ancient solar observing station. Standing on the Northeast side of the boulder at a spot indicated by a spiral petroglyph, the NE horizon is characterized by a sharp pyramidal rock which can serve as an horizon marker allowing anticipation of the summer solstice.

The petroglyph can be interpreted as a schematic depiction of the solar corona at times of eclipse; the central, solid disc is the eclipsed Sun, which is surrounded by elongated features of a length comparable to the solar diameter, distributed all around the solar disc. This is a tolerable depiction of the solar corona at times close to the maximum in solar activity, when "helmet streamers" are found at all heliocentric latitudes (total eclipse image and Yohkoh X-ray images from The Sun: a Pictorial Introduction). If one accepts this interpretation, then the pecked solid dot to the upper left of the eclipse petroglyph can be interpreted as the planet Venus, whose daytime appearance near the eclipsed Sun is often a visually striking sight at time of total eclipse. Once again this represents a plausible conjecture, for which proper cultural context is yet to be established

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The Sun Dagger

kolinski — Wed, 26 Jan 2022 20:24:32 +0000

The Sun Dagger kolinski Wed, 01/26/2022 - 13:24

The 2-3 meter sandstone slabs, at Fajada Butte in Chaco Canyon, cast shadows of the late morning and midday sun to indicate both solstices and equinoxes.The first, clearly visible on this photograph, is a large spiral, 34 cm high and 41 cm wide. The spiral numbers nine and a half turns, moving outwards and counterclockwise from its center. The second, much smaller petroglyph is a coiled snake form, located higher and to the left of the large spiral, and is hidden from view here.

The "Sun Dagger" light configuration at summer solstice.

Paul Charbonneau, © High Altitude Observatory, National Center for Atmospheric Research

At the summer solstice, before midday, the shafts of light illuminating the cliff face interact with the large spiral in a visually striking manner. Shortly past 11:00am local solar time, a small spot of sunlight first appears above the large spiral. It lengthens vertically into a very narrow, downward pointing elongated triangle (or "dagger"). The dagger continues growing and moving downward until, around 11:15am, it cleanly bisects the spiral almost over its entire height. At this point the Sun is high enough in the sky for the overhang above site to begin casting a shadow on the slabs, and in doing so cuts off the upper end of the dagger. This leads to the dagger as a whole moving downwards while maintaining approximately the same length, until it slips off the cliff face and disappears completely. The whole event lasts a little over 20 minutes. On the winter solstice a = similar sequence of events unfolds, except that this time two light shafts illuminate the cliff face. Once again the shafts start off as small light spots above the spiral, and subsequently stretch downward until they bracket the large spiral. At the equinoxes a long, thin shaft of light illuminates the large spiral off center, but a second, smaller shaft bisects the coil on the smaller snake petroglyph.

Recall from slide 4, Horizon Calendars, that shortly before local solar noon the Sun is moving almost horizontally across the sky. To produce a downward moving light pattern then requires the interaction of two inclined or curved surfaces. Here the needed surfaces are situated near the top of the slabs. It has been suggested that those critical surfaces were further shaped by the Anasazi, but the faint pecking marks noted as supporting evidence for this hypothesis are effectively impossible to distinguish from naturally occurring sandstone weathering patterns.

In 1982 the National Park Service restricted public access to the site, for fear of accelerating erosion and soil loss around the slabs caused by increased visitor volume. Those fears were unfortunately well-founded. In 1989 it was noted that the summer solstice light pattern was altered, due to slight shifting of two of the sandstone slabs. The Sun dagger, as seen on this slide, is now considerably thicker than it was when first studied in the late 1970s. In addition, rather than moving vertically downward, the dagger now forms slightly left of a vertical line bisecting the spiral, and drifts towards center as it moves downward. Subsequent observations revealed that the winter solstice and equinox patterns were severely altered, as compared to the patterns recorded when the site was first studied. A retaining wall was built around the base of the slabs to prevent further erosion and slab movement, and at this writing access to the site is only allowed for yearly site monitoring.

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The 3-Slab Slit

kolinski — Wed, 26 Jan 2022 20:04:39 +0000

The 3-Slab Slit kolinski Wed, 01/26/2022 - 13:04

The three sandstone slabs located at the foot of the uppermost 10-meter high cliff band of Fajada Butte are 2 to 3 meters high, 0.7 to 1 meter wide, and 20 to 50 centimeters thick. They are estimated to weigh each around 2 metric tons (2000 kg). Geologic evidence indicates that the slabs were originally part of a single large block which broke off from the cliff face to the left of their present position and toppled over, fracturing along two weaker bedding planes upon impact. The three slabs do not touch, being separated from each other by narrow gaps about 10 centimeter wide. The solar marker nature of the site was discovered serendipitously in 1977 in the course of a survey of petroglyphs on the butte.

The three slab site on the East face of Fajada butte.

The slabs rest almost vertically against the smooth cliff face, fanning out to the South. They form the side wall and roof of an elongated triangular niche which remains shaded except around midday when sunlight shines through the openings between the slabs. The cliff wall is illuminated in this way for about 25 minutes near summer solstice, and up to three hours near winter solstice when the Sun is lower in the sky. A large rock overhang situated above the site (visible on this photograph) shades the slabs when the Sun's altitude exceeds 75^o.

Considerable controversy regarding the possible man-made nature of the 3-slab site developed following the first reports of its operation as a solar calendar. Further studies yielded several lines of evidence indicating that the site is the result of a natural rockfall, rather than an Anasazi construct. The Anasazi were not in the habit of using large stones for their constructions, except as foundation for the large roof posts of their great kivas. Even then, the slabs are some five times heavier than the heaviest such foundation stones unearthed in Chaco Canyon. The Chacoans were clearly very adept at masonry work, and have been known to construct supporting walls to buttress large rocks perched in positions posing a threat to their dwellings, most notably behind Pueblo Bonito. Yet no sign of any such reinforcement work is to be found around the 3-slab site. It has also been noted that geological formations resembling the 3-slab site are common throughout the canyon, and examination of the base of the slab indicates that a piece of one of the slab broke on impact, arguing against the slabs being artificially positioned by human hands.

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Fajada Butte

kolinski — Wed, 26 Jan 2022 19:57:51 +0000

Fajada Butte kolinski Wed, 01/26/2022 - 12:57

Fajada butte, Chaco Canyon, at sunrise on 21 June 1997, seen from the Northeast.

Fajada butte ("banded butte") rises 115 meters above the canyon floor to an elevation of 2019 meters. It stands in a prominent 3 kilometer wide gap in Chacra Mesa, which delineates the South wall of Chaco Canyon. The summit of the butte offers commanding views of the canyon and of the vast expanses to the South, and as such, makes a unique observation site, either for astronomical or surveillance purposes. Despite the difficulty of the climb up the butte and the lack of available water, ruins of a few of small dwellings are found along some of the higher cliff bands around the butte. Analysis of pottery fragments recovered on the butte indicates that it was at least visited starting in the tenth century.

In recent years evidence has been uncovered that a large ramp had been built on the SW face of the butte, to facilitate its ascent. 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. The so-called 3-slab site (next slide, The 3-Slab Slit) is located at the foot of the uppermost 10-meter high cliff band, approximately at the center of the butte as seen on this photograph.

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Solstice Marker

kolinski — Wed, 26 Jan 2022 19:50:48 +0000

Solstice Marker kolinski Wed, 01/26/2022 - 12:50

On summer solstice, the petroglyph panel of the previous slide takes part in a striking play of light. About 45 minutes after sunrise, a thick pointed shaft of light appears to the left of the petroglyphs, and gradually moves rightward, cutting across the top part of the leftmost spiral (top left image on the photograph).

Path of summer solstice light on three petroglyphs.

A second knife-like light spot appears to the right of the second spiral, and stretches horizontally in both directions, nearly bisecting the spiral (top right). Meanwhile a third, thin shaft of light has begun to form to the right of the Sun-symbol at the other end of the panel (bottom left). It grows leftward into a thin "light serpent" that cleanly bisects the Sun-symbol and continues to stretch leftward (bottom right) until it touches and merges with the left light shafts. At this point the three petroglyphs are linked by a long shaft of light along the whole length of the boulder. This sequence of events unfolds in a little under ten minutes.

The Holly House "light serpent" certainly offers a visually striking confirmation of summer solstice. Of course, other light configurations can be seen shortly after sunrise at other times of the year. Light is first seen in the tunnel late in February, and the Sun-symbol is briefly illuminated around the vernal equinox, and again in various ways from mid-April to mid-May. It has been suggested that these evolving light patterns might have served to define a planting calendar. From end of May to end of July, the day-to-day vertical displacement of the rightmost light shaft with respect to the Sun symbol is certainly large enough to make anticipatory observations to predict the summer solstice.

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prehistoric-southwest

Credits

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Supernova Pictograph

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Lunar Astronomy

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Cliff Palace

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The Sun Temple

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Solar Eclipse Petroglyph

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The Sun Dagger

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The 3-Slab Slit

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Fajada Butte

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Solstice Marker

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