January 30, 2020 11:59AM
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Registered: 4 years ago
Posts: 170
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Hi Brendan,
Thanks for your post.
The main reason why Rawlins and Pickering proposed their method was one significant weakness of Spence's "simultaneous transit" method. She chose a reference pair of stars Mizar-Kochab, each of which was relatively far from the celestial Pole, and therefore the diurnal rotation of the sky was very quickly carrying these two stars aside from vertical (in my article, I estimated that these two stars was diverging by 2' in the vertical establishment in just 15 seconds). As astronomers, Rawlins and Pickering understood the difficulties that an observer so limited in time would have faced, therefore they proposed an ingenious method in which horizontal establishment was used for two stars (Thuban and 10 Dra) located as close to the Pole as possible (due to the proximity to the Pole these stars have had very small linear velocities of rotation, what theoretically would allow observations to be made with an allowable error for several dozens of minutes).
Rawlins and Pickering method also has another strength. Any orientation method should have been somehow invented, some observations should have helped its creators to invent it. So, in the case of Rawlins and Pickering method, ancient astronomers could notice that two relatively faint stars (Thuban and 10 Dra) move very little during the rotation of the sky and the center of rotation is close to the midline between them. Thus, a method of orientation towadrs this invisible center of rotation could be invented. In the case of Spence's method, the choice of a pair of stars is not argued in any way, and it is impossible to guess with the help of which observations this method could be invented, so I consider this idea to be extremely ephemeral. Also Spence most likely used Gensler's idea of observation of vertical establishment of two stars with the help of merkhet (Zaba (1953) mentioned this idea). Spence reffered to Zaba but modestly kept silent about Gensler.
At now let us turn to your question - why is Meskhetiu better than Thuban for alignment of the pyramids.
It is shown in my article that all the pyramids of the 4th dynasty (with the exception of the Djedefre pyramid) were oriented towards Thuban. Three pyramids of the 3rd dynasty, a pyramid of Djedefre and two pyramids of the 5th dynasty were oriented towards the stars of Meskhetiu (I do not know how to insert a picture in this phorum).
What caused the choice of a particular star is not yet entirely clear (it is very interesting question for future research), but I can assume the following: most likely the orientation of the funerary complexes to the stars of Meskhetiu in its sacred position (Aq) existed in the Early Dynastic period (I can't prove this, because there are no accurate data on azimuths of these structures) and was continued at the times of the 3rd dynasty. Snofru introduced certain change in tradition and the pole star - Tuban - was used as a reference star by several generations of his successors. Djedefre obviously made an attempt to return to the old tradition. As for the 5th dynasty, nothing can be said for sure, because only a few pyramids are accurately measured. The data for Sahure, Unas, and Teti seem to confirm the assumption that after Thuban moved away from the Pole, there was a return (maybe partial return) to the old tradition of orientation to Meskhetiu.
In any case, not one of the orientation methods that I read about (Spence, Rawlins and Pickering, Belmonte) goes beyond explaining the orientation of the pyramids of the 4th dynasty. All bisector methods (Petrie, Edwards, etc.) have problems explaining the orientation of the pyramids of the 3rd dynasty, the pyramids of Djedefre, Teti and several other cases.
Best,
Alex.
Edited 7 time(s). Last edit at 01/30/2020 12:11PM by keeperzz.
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Hermione |
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