FOR RELEASE: 10 a.m. CST, January 6, 1999.
A CENTRAL TEXAS SUN DAGGER
In a paper given to the American Astronomical Society in Austin, Texas, archaeoastronomer R. Robert Robbins of the University of Texas Astronomy Department at Austin reported on the results of almost two years of observations of an unusual seasonal interplay of sunlight discovered among many of pictographs (Indian rock art) at Paint Rock in central Texas. The site is on private land, and the owners, Kay and Fred Campbell, have acted as protective custodians for years but giving occasional guided tours to interested groups.
Alerted by an accidental discovery of some curious solar behavior, the owners contacted Dr. Robbins, who found that dramatic daggers of sunlight strike the rocks at winter and summer solstice and shine on pictographs clearly drawn in the rocks to receive them. Further, these daggers of light reach their maximum altitude in the rocks at a time that agrees with solar apparent time to within a few minutes. Their behavior strongly suggests that the Indians using this territory (the Tonkawa and the Jumano, then later the Apache, Kiowa, and Commanche) and were constructing and making use of seasonal markers that exhibit a higher degree of calendrical skills than has generally been attributed to them. This solar timepiece would allow the various hunter-gather tribes to successfully assemble and conduct necessary business, as well as seeking shelter from the winter.
Paint Rock would seem to be an ideal place for "winter Texans." A south-facing bluff about half a mile long and 30-40 feet high provides natural shelter against north winds. In the summer, the site would provide shade and breezes created by the Concho river, less than 100 yards away. There are some indications of habitation of this area back to 6000 BP and you can even find the names of known Indians in the rocks.
Figure 1 shows a snapshot of the behavior seen at Paint Rock at the time of the 1997 winter solstice (December 21), when the apparent sun was as far south in the sky as it can get. At 12:27, a spot of light is just reaching the red shield glyph, and as the light moves, it quickly acquires a dagger or spearpoint shape. At 12:37, the dagger reaches the center of the painting. This is also the maximum altitude for the light, as it begins to slide off of the glyph to the right.
The timing of the event is remarkable. After correcting for the longitude of Paint Rock and also applying corrections for the ellipticity of the earth's orbit around the sun (the Equation of Time), the local apparent time at maximum altitude is within 5 minutes of the sundagger value.
There is no evidence (yet) of interest in sunrise and sunset points on the horizon, but this has not been carefully investigated. However, the landscape is not very amenable to that type of observation, being quite flat in all directions. The solar event at Paint Rock concerns the middle of the day, when the sun is reaching its maximum altitude.
According to D. E.. Sims, who purchased the ranch in 1878 and had many interactions with the local Indians, the "shield" painting signified a council meeting conducted by five bands of Indians to divide hunting lands. The number 5 does appear twice in the painting design . It is clear that the solar behavior was noted and the pictograph was then properly constructed. It seems unlikely that it was coincidence. Nevertheless, this is discussed below.
One obvious technique for protection against coincidence is to formulate a further hypothesis that requires finding additional and new relevant data. For example, in this case, we could argue that our winter solstice interpretations would be strengthened if we could find evidence for a summer solstice "show" as well. But observing a possible summer solstice is easier said than done. How do we patrol a mile-long blackboard dense with art 30 feet up, when the event might be anywhere or perhaps brief? Apart from bringing in an entire bus of observers and spread them out along the cliffs, it seems daunting.
Mythology can often help make useful connections, so I narrowed down the ground to be covered by paying particular attention to representations of turtles. Turtles are a popular theme at Paint Rock as they are in Mesoamerica, where the slow-moving turtle symbolized the solstice -- the times of the year when the apparent Sun moves most slowly in the sky. Observing on June 21, 1998, I located the largest and most elaborate turtle pictograph and waited. And I was rewarded by the appearance of a new sun dagger, at some distance from the winter solstice shield glyph. Figure 2 shows the summer solstice spear of light and at the bottom, the turtle painting. It began to develop at approximately 1:40, again within 5 minutes or so of its expected passing of the meridian.
For summer solstice, it is easier to see the path of the light through the rocks (see Figure 3). A narrow slot between two boulders passes light only when the sun is near the meridian -- the imaginary circle on the sky separating east from west. Figure 4 shows the bluff itself and it may be possible to see the turtle with small daggers slightly to the right of the center of the photograph. The existence a summer solstice event increases the likelyhood that the winter solstice event is also real.
Equinox interpretations are somewhat more problematic but not ruled out; they will be studied in the year to come. But there is certainly more to be found at Paint Rock. For example, below the shield painting, behind a large boulder that appears to have slipped downhill, there is a sequence of red hematite vertical lines about 1" apart. Counting them gives 15, rather close to the age of the Moon in days when an eclipse can occur. The lines are very sheltered in the rocks, suggesting they were tallies rather than observations.
The discovery and interpretation of pictographs and petroglyphs becomes harder every day, as oral tradition weakens and graffiti and bulldozers cover the land. There is some urgency, to preserve what we can and learn as much as possible, as our direct knowledge of the original Native Americans dwindles. Many sites are on private lands and we should make every effort to meet their owners and develop good relationships. There is still much to do at Paint Rock, not to mention all the many sites still to be discovered. Low tech has its place in the "techniques" section of the researcher's handbook.
The author of this paper may be contacted at e-mail firstname.lastname@example.org