Audrey Wrote:
-------------------------------------------------------
> Jon Ellison Wrote:
> --------------------------------------------------
>
> > The external field of view from the bottom of the
> > DP is about 0.7 deg vertical, 0.5 deg horizontal.
> > You could always stand six inches inside, then
> > you'd have a whole half sky to look at. Pick any
> > star you like.
> > Without light pollution, a veritable star soup.
>
> That's good to know - thanks! I didn't know how to calculate it.

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 (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 horizon.

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.




Edited 6 time(s). Last edit at 23-Feb-17 03:29 by Origyptian.