Towers to Track the Sun

Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1189e
DOI: 10.1126/science.315.5816.1189e

Both archaeological sites and written and spoken records document that the Incas were making careful solar observations about 500 years ago, but evidence for earlier observational activity has been difficult to obtain. Ghezzi and Ruggles (p. 1239; see the news story by Mann) now describe a series of 13 stone towers that date to 2400 years ago that are arrayed north-south along a hill in the center of a temple complex in coastal Peru, and show that these towers marked the annual rising and setting arcs of the Sun and served as a calendar accurate to a few days. Thus, these towers and the surrounding temple evidently served as an early solar observatory.

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