The 140-foot-wide suspected Hohokam
observatory at Shaw Butte.
(Todd Bostwick)
Two Disciplines Align to Shed Light On Astronomy of the Ancients
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PHOENIX—At first glance, the jumble of rocks resting on an undeveloped mountain 300 feet above the sprawling and congested city of Phoenix hardly seems extraordinary. But the rocks, long assumed to have been an ancient Hohokam Indian fortress, recently caught the attention of scientists who suspect they may have served a less warlike purpose: allowing the Hohokam to track the sun and the seasons.
"The Hohokam seem to have had a more sophisticated knowledge of astronomy than we'd recognized," says Phoenix city archaeologist Todd Bostwick, who along with amateur astronomer Stan Plum came up with the new theory. "As modern-day humans, we ignore half of our world -- the sky. But for people in the past, that was their world."
Bostwick is just one of a small band of self-styled "archaeoastronomers" who are creating excitement and controversy in the often-insular worlds of archaeology astronomy.
Archaeoastronomy, which counts about 200 serious practitioners today, attempts to divine what ancient societies knew about the moon, the sun and seasonal cycles by studying archaeological relics for important "interactions" with celestial bodies, such as a shaft of sunlight that pierces a hole in a wall only on the day of the summer solstice. Some archaeoastronomers use these findings to speculate on how such societies organized their religious ceremonies or their social structures.
Archaeoastronomy was long shunned by academic archaeologists and astronomers, in part because university professors were often outnumbered by a variety of inspired -- but sometimes fringy -- amateurs. And even the credentialed academics who ventured into archaeoastronomy often faced sniping.
One early theory -- that an Arizona site called Casa Grande could have been used for celestial observations -- was so widely derided in 1969 that the scholar who proposed it was all but drummed out of astronomy. Then, in the 1980s, University of Arizona astronomer Raymond E. White argued that portions of the Inca ruin Machu Picchu had served as an observatory. White recalls that when he delivered an address on the topic, critics came up to him and said he was "crazier than a tick."
"It's been difficult," acknowledges W. Bruce Masse, whose studies linking Hawaiian oral mythologies and celestial events such as comets and supernovas have attracted both praise and criticism. Masse, by day an archaeologist who preserves Indian historic and sacred sites for the Air Force, explains that "part of the problem is that archaeoastronomy brings together people from different disciplines who share no common language. Archaeoastronomers have to learn both disciplines, which requires a lot of effort. That's one reason why we'll never be truly mainstream until archaeoastronomy becomes part of the core curriculum."
Recently, though, archaeoastronomy has prompted a flurry of popular books, and the scholarly attacks have begun softening. Recent findings, such as Bostwick's, have been presented -- often with scholarly approval -- at a growing number of academic conferences devoted to the specialty.
"Archaeologists have a number of resources to work with, including structures and artifacts," says Bob Preston, an astronomer at NASA's Jet Propulsion Laboratory in California. "Archaeoastronomy gives them another tool. What archaeoastronomy has that the other tools don't is a unique insight into a society's ceremonial life. Because all cultures have cosmologies of some sort, archaeoastronomy is alive in a way that much of archaeology is not."
E.C. Krupp, the director of Los Angeles' Griffith Observatory and the author of several books about archaeoastronomy, says he doesn't hear much direct criticism these days except from archaeologists and astronomers. "That criticism is often correct, such as when people are accused of not doing their cultural homework or of not putting their findings in the proper context," he says. "People are asked, fairly, how they can talk about Mesoamerican pyramids without knowing about the social structures of the societies that produced them."
Bostwick's discovery is one receiving cautious praise from other archaeoastronomers. His personal interest in Indian rock art first led him to notice the interplay of light and shadow on the rocks at Shaw Butte. Feeling he needed enough sightings throughout the year to be sure that the patterns were more than coincidence, took three years of study before announcing his conclusions about the 800-year-old site.
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Krupp and Preston agree that the other main challenge facing archaeoastronomers is the temptation to over-promise. For instance, Bostwick suggests that once scientists agree that Shaw Butte was actually an observatory, they must entertain the possibility that the Hohokam had an elite, astronomically aware caste -- something that would contradict current extrapolations of their society. While Bostwick makes a point of calling this idea speculative, Krupp and Preston say that not all archaeoastronomers are so careful.
While many recent archaeoastronomical findings suggest that ancient cultures had a surprisingly broad knowledge of celestial events, Krupp says these findings mainly highlight our own modern-day condescension. "The fact that there is astronomy built into Stonehenge should not be that surprising to us, because the site's engineering and construction is at least as complex as its astronomical orientation is."
Archaeoastronomers also have more immediate worries. Not long after Bostwick's theory was publicized, vandals toppled a crucial rock at the Shaw Butte site, changing forever the observatory's alignment. "Taxpayers pay for the use of parks, and they feel they have a right to visit the site," Bostwick says. "But it's a delicate balance between allowing controlled visiting while still protecting the site and ensuring its safety. What's pressing a lot of us is saving the sites first. We need to document, document, document."
