Kanga: “Thanks for the correction. It does appear that you were the first to correlate the KCS shaft to Al Nilam. However, the date appears to be wrong. The date depends on what software you are using. With Stellarium, the date of alignment is -2552, not -2570. Stellarium should be used because it takes into account atmospheric refraction.”

All serious sky simulators factor in atmospheric refraction. The program I use corrects for precession, nutation, proper motion, light time, aberration, and atmospheric refraction. I also use other programs including Stellarium, and Starry Night Pro Plus 7, and I usually compare results between these.

Piazzi Smyth knew all about refraction:

“…if the original designer had wished that men should see with their bodily, rather than their mental eyes, the pole of the sky from the foot of the Great Pyramid, at an altitude before them of 30°, he would have had to take into account of the refraction of the atmosphere; and that would have necessitated the building standing not in 30°, but in 29° 58’ 22”. (‘Our Inheritance in the Great Pyramid’ 1874: 61)


I also use Glen Dash’s 2018 survey coordinates for Khufu’s pyramid:
29° 58’ 45.05570” N (29.97918° N); 31° 08’ 03.11209” (31.1342° E)

Over a decade ago, I estimated that c.2570 was a close approximation for an astronomical date based on the upper shafts, but I recognised that many variables affect the accuracy of the date, which is why I wrote 2570 as c.2570 - circa 2570 which means approximately 2570 - in fact I wrote many years ago that perhaps accurate to within +-10 years.

Since then I refined the date to c.2555 BC but even this date is only approximate as the same variables apply.

For example, last year I wrote: “According to Gantenbrink, the upper southern shaft has an average angle of incline for the final 42m of 45 degs, which means an alignment to the 3-star asterism in Orion was c. 2555 BC.”

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Some variables:
The pyramid was not built according to the tolerances of a Swiss precision watch, but to building tolerances.

The shafts presented a difficult challenge for the builders - they had difficulty in maintaining a straight line and a consistent angle of incline.

The outer casing has been forcibly removed, and together with the dynamiting inside the pyramid above the lower section of the shafts and earthquakes, probably caused some movement or subsidence in the shafts that would affect the angle of incline.

The pyramid is slightly skewed from anywhere between 2 - 5 arc minutes from the cardinal points, which means the direction of the shafts is not precisely due north/south.

Some variables have a negligible affect on the angle of incline but for example I calculated a range of dates for Alnitak using the various angles found at the top end of the upper south shaft:

2589: 44.84° (44° 50’ 24”)
2575: 44.9102° (44° 51’ )
2555: 45.00° (the probable intended angle)
2535: 45.11°

Chris