In Peru, scientists discover the oldest solar observatory in the Americas

As archaeologists evaluate whether an ancient temple in Buena Vista, Peru, functioned as a calendar, a different research team is preserving the remains of an unusually elaborate astronomical complex just north, in Chankillo. This solar observatory is considered the oldest in the Americas, dating back to the 4th century B.C., and it offers unique physical evidence that a sun cult inhabited Peru at least 1,500 years before the Incas.

“We have references that Incas practiced solar observation, but none of those sites have been preserved,” says the site’s lead archaeologist Ivan Ghezzi of Yale University and the Pontifical Catholic University of Peru. “We don’t have a single one of this complexity.”

Though Spanish chroniclers described “sun pillars” used by the Incas to mark specific solar events, the physical remains of these pillars—likely destroyed during 16th-century anti-idolatry campaigns—have not been found. Archaeologists have uncovered the base of two pillars on an island in nearby Lake Titicaca, but the observatories in Chankillo appear more sophisticated than any of these Incan structures, says Ghezzi, who published his findings along with coauthor Clive Ruggles of the University of Leicester, in Science last month.

The Chankillo observatory consists of a row of 13 towers that precisely tracked solar movement throughout the year. When viewed from two main observation points, the sun would have reached one end of the tower line at the winter solstice and the other end at the summer solstice. The regularly spaced gaps between each tower could have been used to divide the year into even shorter intervals of 10 to 12 days.

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