The earth as it rotates performs a slow ‘wobble’, or ‘precesses’ like a spinning top. The visible sky is always changing very slowly. Today the earth’s axis points towards the star Polaris but 5000 years years ago the pole lay in the constellation Draco –
Thuban at the north celestial pole
In fact at the beginning of the pyramid age the star Thuban in this constellation was only a few minutes from the pole. Being the star that marked the pole at that date, it was a natural stellar candidate to be given sacred meaning, which it may well have retained in times to come even after it had moved away from the pole.
The Egyptians were avid sky watchers and certainly noticed the effects of precession – stars moved. Their ‘explanation’ for this was probably couched in mythological language. The one thing that didn’t move was the abstract concept of the pole, the eternal.
If pyramid builders had simply wished to determine true north to the best of their abilities they could have used a number of methods. Dash showed that quite high precision could be achieved using the sun. But so it can using the stars, by means of a level, a plumb bob, and a backsight. (NOTE 3 STAR SIGHTING)
Tabulated below are the estimated orientations of the major IVth dynasty pyramids –
Change in pyramid orientation over time
The increasing precision in orientation of pyramids to true north has often been put down to improving skills in layout and construction until, with Khufu and Khafre, it was almost perfect. However, if consensus pyramid dates are plotted against pyramid orientations (in minutes from true north) a pattern emerges, taking into account that these are average orientations – the sides of pyramids each have slightly different orientations which complicates the situation. Nevertheless the builders were apparently following a target, and what could that be but a star?
(Djedefre’s pyramid with the somewhat ‘archaic’ design of its passage system, at almost 50 minutes, is outside the range of the graph. Its orientation must be due to other factors. The orientations of Khufu and Khafre are so similar that they seem to have been laid out at the same time).
Conventional dates for pyramids have been calculated by adding the reigns of kings as listed on Egyptian monuments. However these are fragmentary and contain contradictions, and different scholars have come up with a range of dates, but the consensus is that Khufu was started about 2590 BC and work stopped at Menkaure around 2500 BC.
Numerous radiocarbon samples from the pyramids consistently give much older dates. Usually this is put down to the use of old wood. Recently Puchkov has proposed that Old Kingdom pyramids are actually 200 years older than conventional dates – I understand that radiocarbon tests on short-lived organic pyramid samples (like straw) are currently being carried out to test this hypothesis.
Uncertainty in dating makes it difficult to identify which star(s) the pyramid builders might have followed.
Bauval noted that two stars, Mizar in Ursa Major and Kochab in Ursa Minor, were in vertical alignment, or ‘simultaneous transit’ through the meridian in 2467 BC, marking the north celestial pole –
The simultaneous transit of Kochab and Mizar
It was Spence who had the idea of studying the orientations of pyramids and comparing them with the precessional drift of stars (as shown in the chart above), using the same stars as Bauval. But most scholars agree that work at Giza started 100 years before these stars could practically be used for alignment.
Belmonte put forward a different pair of stars, both in Ursa Major – Phecda and Megrez. These were in simultaneous transit around 2560 BC –
The simultaneous transit of Phecda and Merez
These are much better candidates than Spence’s, and both belong to Meskhetiu, the constellation of the bull.
It is interesting to make a comparison with the simultaneous transit of two stars of Orion culminating in the south at the same date. But then perhaps the builders focussed on a single star. The question remains open.