Science: Graffiti with a Heavenly Message

The Southwest's old Indian rock carvings were observatories

As icy winds howled through the canyon, the people huddled beside their fires. The days had become short and cold, and the tribe's store of food was running low. Every day the people asked a tribal elder when the warming sun would return. But Sun Watcher, as he was called, sadly shook his head. The sun father, he said, was still journeying away. Then one day, when it seemed as if the far-off disc had barely risen above the horizon, Sun Watcher's wizened face broke into a smile. The sun father, he announced, had decided to return. The days would become longer, and a new planting season could begin.

Even today the Indians of the U.S. Southwest have their sun watchers.

They proclaim the sun's highest and lowest point in the midday sky, on about June 22 and Dec. 22, (the summer and winter solstices), and signal the advent of a new season. Modern calendars ensure that there are no mistakes. But how did the pre-Columbian peoples foretell the seasons? Apparently, says a husband-and-wife scientific team, the Southwest's ancient inhabitants were skilled solar observers who used rock carvings to keep track of the sun's progress across the heavens.

NASA Astronomer Robert Preston and his wife Ann, an artist, came upon the evidence serendipitously while visiting Arizona's Petrified Forest National Park. The Prestons noticed some old Indian petroglyphs, the technical name for the spirals, crosses, lizards, birds and other rock carvings found throughout the Southwest. Anthropologists have tended to view them as little more than ancient graffiti, but the Prestons saw a message. As sunlight filtered between two large rocks, it formed dagger-like beams that swept tantalizingly across the petroglyphs. At once the Prestons suspected that the carvings might be a little solar observatory.

The first hint of astronomy among the Southwest's original settlers had come a few years earlier when Artist Anna Sofaer was photographing spiral petroglyphs in New Mexico's Chaco Canyon, once the center of a flourishing Indian civilization. The carvings had been left by the area's former inhabitants, the Anasazi. For hundreds of years they lived in the canyon, creating astonishing multistoried cliff dwellings, only to vanish mysteriously at the start of the 14th century. Sofaer, visiting the site around the time of the summer solstice, noticed that a beam of sunlight sliced right through one large spiral.