- 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 5 years.
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- While the Giza pyramids have not been accurately dated
before, investigators have marveled at the accuracy with which they are
aligned to the compass' 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.
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- 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.
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- 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.
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- 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.
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- 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 5 years due to pyramid measurement errors as
the date for the start of the pyramid's construction.
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- 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.
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- 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."
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- 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."
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- 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.
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- 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.
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- 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.
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- Meanwhile, 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.
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