> As a rough approximation, the vertical angle of
> view of a 4' high entrance when viewed from 344'
> at the bottom of its linear DP excursion, is:
- tan-1 x (4/344) = 0.67 degrees
> ...which puts it at 26.5 +/- 0.335 degrees which
> is a range of 26.165-26.835 degrees above the
> Thuban would be at its closest alignment with
> celestial north around 2800 BC when it would be
> just under 1 degree off that axis which, in Cairo,
> is at 30 degrees above the horizon (similar to
> Polaris). Therefore, in 2550 BC Thuban would be a
> bit farther than 1 degree off the
> celestial axis (ie, > degrees) but would it be
> greater than 3.165-ish degrees off-axis so that it
> could just barely show up in the DP portal?...
> ...First consider that Polaris currently is about
> 0.75 degrees off celestial axis, and I've read
> that it will be only 0.4525 degrees off-axis (its
> closest alignment this precessional cycle) in
> 2100. And so, about 80 years from now it will have
> moved 0.3 degrees.
> Therefore, doing a rough extrapolation with
> Thuban, the difference between its closest (less
> than 1 degree off the 30 degree axis) alignment in
> 2800BC and the alleged construction of G1's 26.5
> degree DP in 2550 is about 250 years which is
> about 3 x 80 years or 3 x 0.3 degree shift further
> off-axis, The resulting accumulated shift of
> about 1 additional degree still will put Thuban at
> >28 degrees above the horizon at its lowest point
> and it will not be visible within the 26.5 degree
> DP located at 30N latitude that can only view
> objects up to 26.835 degrees above the horizon in
> 2550 BC.
Thank you! Isn't it great when people collaborate with real data.