Stars Date Egyptian Pyramids

Guided by stars? The pyramids at Giza might have been aligned to two northerly stars.

By looking at the stars, an Egyptologist claims to have found a new way to date the pyramids of Giza and other ancient sites. According to her calculations, construction on the Great Pyramid started about 75 years later than the currently accepted date. If she's right, Egyptologists may have to rewrite their timelines.

One of the many mysteries of the pyramids is how and why each was built with a precise north-south alignment. The square base of the Great Pyramid of Cheops, for instance, is just 3.4 arcminutes off of true north. That's a precision of about 1 millimeter per meter. Some of the later pyramids, however, deviate more, as if their architects' method for aligning them became less accurate over time.

Suspecting that the heavens might have played a role, Egyptologist Karen Spence of the University of Cambridge, United Kingdom, tested whether two stars called Kochab and Mizar could account for the pyramids' orientation. In the middle of the third millennium B.C., the north celestial pole lay halfway between those two stars--at least in 2467. Before and after that date, a slow shift in Earth's axis skewed the alignment of the two stars with the celestial pole ever so slightly. According to Spence, this drift accounts for the change in pyramid orientation over the years. Using the locations of Kochab and Mizar, she determined the start of construction of the pyramids to within 5 years, she reports in the 16 November issue of Nature.

"Egyptologists are now faced with the challenge of fitting these new dates in their chronologies," says Maarten Raven of the National Museum of Antiquities in Leiden, the Netherlands. He was surprised by the originality of the idea and is "convinced by its simplicity." But he says that more accurate measurements of pyramid orientations are needed to confirm the theory.

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