Bonapart's Expeditionary Force Survey; 1798
Since the 19th century many archeologists have developed the idea that alignment
of the Egyptian pyramids at Giza harks back to one of the first moments in the
history of civilization in which astronomy was pressed into the service of the arts, in
this case to monumental architecture. In particular, the pyramids of the IV Dynasty
Kings Cheops, Khephren and Mycerinus, are orientated with extraordinary
accuracy with the four cardinal points of the modern compass.
The British Egyptologist, K. Spence has suggested that the alignment of the
pyramids in relation to the cardinal points of the modern compass could have been
achieved via observations of simultaneous transits across the local meridian (an
imaginary semicircle that divides the sky into its eastern and western halves) of two
circumpolar stars, Kochab and Mizar, that were on opposite sides of the north
celestial pole at the time when the pyramids were built. If this is true, the
chronology of the Great Pyramid is shortened by almost 80 years. The article by the
IAC's Juan Antonio Belmonte now critically examines Spence's proposal and
improves on this with a new hypothesis.
Responding to Spence's ideas, J.A. Belmonte suggests that this orientation,
following the local meridian, could have been achieved through meridian transit
observations of the stars Phecda and Megrez, belonging to the Leg of the Bull, one
of the most imporatant Egyptian constellation (equivalent to our Plough in the
constellation Ursa Major). Extending the line joining these two stars leads us to
Thuban (the "pole star" at that time) in the same way that the two stars Merak and
Dubhe today act as pointers to the present Pole Star, Polaris.
According to this new hypothesis, the greatest accuracy of alignment would have
been achieved around the year 2562 BC; consequently, the Great Pyramid could
have been orientated close to this date, at a moment falling between the two dates
proposed Spence and Belmonte, which would place it at the start of the reign of
Cheops (2589 - 2551 BC) and render unnecessary the shortening in the chronology
advocated by Spence.
Belmonte's hypothesis has important chronological and historical - even
mythological - implications that could help towards a a better understanding of how
the Egyptians of the pharaonic era understood the cosmos and made use of it,
among other things, to align precisely their most important monuments.
The ancient Egyptians were extremely interested in the night sky, articularly the
circumpolar stars. These stars circle around the North Pole, and as you can always see
them, the Egyptians always referred to them as 'The Indestructibles'. As a result, they
became closely associated with eternity and the king's afterlife. So that after death, the
king would hope to join the circumpolar stars - and that's why the pyramids were laid out
towards them.
The north-finding stars were Kochab, in the bowl of the Little Dipper (Ursa Minor), and
Mizar, in the middle of the handle of The Plough or Big Dipper (Ursa Major).
An Egyptian astronomer would have held up a plumb line and waited for the night sky to
slowly pivot around the unmarked pole as the Earth rotated.
When the plumb line exactly intersected both stars, one about 10 degrees above the
invisible pole and the other 10 degrees below it, the sight line to the horizon would aim
directly north.
However, the Earth's axis is unstable and wobbles like a gyroscope over a period of
26,000 years. Modern astronomers now know that the celestial north pole was exactly
aligned between Kochab and Mizar only in the year 2,467 BC.
Either side of this date, the ancient astronomers trying to find true north would lose some
accuracy.
Spence shows that the orientation errors of earlier and later pyramids faithfully track the
slow drift of Kochab and Mizar with respect to true north. And because the error in the
Kochab-Mizar alignment can be readily calculated for any date, the error in each
pyramid's orientation corresponds to a period of several years.
