British archaeologist, Kate Spence, has a novel solution to an Egyptian mystery. It explains how ancient surveyors could have used stars to orient the pyramids at Giza when they had no pole star to guide them. It reduces the uncertainty in the start date for Great Pyramid construction from a century to a mere five years
While the Giza pyramids have not been accurately dated before, investigators have marveled at the accuracy with which they are aligned to the compass's cardinal points. The western and eastern sides of the Great Pyramid, in particular, align with true north to within 3 arcminutes - about a tenth the width of the full moon.
No one has explained such surveying skill satisfactorily. Polaris had not yet taken up its position as our North Star guide. Now Dr. Spence at the University of Cambridge in England has found two other stars on either side of the pole that, taken together, do the job. One - Mizar - is in the middle of the Big Dipper's handle. The other - Kochab - is in the Little Dipper's bowl. Twice a day these stars line up vertically - each lying about 10 degrees from north. An imaginary line between them passes near the celestial North Pole. That line ran very close to the pole at the time of Egypt's Old Kingdom when the Giza pyramids were built 4,400 to 4,600 years ago. It actually ran through the pole in 2467 BC.
To find north, a surveyor had only to wait until the daily rotation of the heavens brought that stellar lineup into coincidence with a vertical plumb line on Earth.
Spence notes that the Great Pyramid is the most accurately aligned of the Giza group. She also notes that the stellar lineup gave the most accurate northerly direction in 2467 BC. Therefore, she picks that date with an uncertainty of five years due to pyramid measurement errors as the date for the start of construction.
Previous dating based on tracing the lengths of the reign of successive kings dated construction to that general period but couldn't come closer than 100 years. Radio carbon dating couldn't do any better.
Harvard University science historian Owen Gingerich calls Spence's theory "the most interesting idea to come down the pike in a long time for aligning the pyramids." A century or more of attempts to explain the alignments astronomically had been disappointing. Dr. Gingerich says that he was ready to dismiss this latest effort out of hand when the journal Nature, which published Spence's account Nov. 16, sent it to him for comment. But he adds that, as soon as he read it, he realized "this is a very serious paper."
He notes that one of its most persuasive aspects is the way Spence's theory neatly accounts for the history of small deviations from true north in the pyramids' construction.
Beginning with the earliest pyramid, surveyor's errors become progressively smaller until they reach a minimum with the Great Pyramid. After that time, they became successively larger. This history correlates with the way the Kochab-Mizar lineup first comes closer to true north and then moves away due to the wobbling of Earth's axis.
The axis traces a circle on the sky every 26,000 years. This changes the positions of stars as seen from Earth. Ancient Egyptians would not have noticed this unless they kept systematic astronomical records for which there is no evidence. Spence says there's more research to be done. She calls the ability to fix the pyramid dates "an advance in establishing a reliable absolute chronology for the second half of the third millennium BC." But, she adds, "it does not solve all the problems." This dating has to be fitted into the full historical sequence.
(c) Copyright 2000. The Christian Science Publishing Society