A 2492 BC date for Alnitak, 45 deg alt. at Giza's lat., was calculated by S.F. Tonkin to a precision of 0.01 degs (36 arc seconds) and verified using Guide v8.0.

I double checked again with SkyChart III, which I use. This time I set the precision to the highest possible level, and Alnitak was more or less at 45 deg alt. 2491...2495. In 2500 it was 44.98 degs alt. which is only a miniscule 2/100 ths of a degree off 45 degs.


A few years ago, I inquired about the accuracy of the astronomy program SN - the response was that star positions relative to other star positions are accurate but star positions relative to the local horizon might be a bit off - by how much they didn't say.

CT