Now You See It, Now You Don’t - The Stones and the Stars: Building Scotland's Newest Megalith - page 21

F IG . 2.3 Ecliptic coordinates (Drawing by Nick Portwin)
(Fig. 2.3 ) . About 13,000 years ago the north pole star was Vega in
Lyra, and 5,000 years ago it was Thuban in Draco, at the time of
Stonehenge I. The pull makes the equator move around the eclip-
tic, constantly changing the position of the vernal and autumnal
equinoxes (precession of the equinoxes, first described outside
the Arab world by Robert Grosseteste in the thirteenth century).
As a result a star's declination is constantly changing - likewise its
right ascension, which is measured from the vernal equinox along
the equator, in the same direction as the Sun's motion on the ecliptic
shown by the arrows in Fig. 2.2 .
When the pyramids were built the Pole Star was not Polaris
but Thuban, the brightest star in Draco. Polaris, which passes
closest to the pole very soon now, has been regarded as 'fixed' in
the sky for most of the last 1,000 years - Shakespeare has Julius
Caesar compare himself to it for constancy - though Columbus
realized it had to be making a small circle in the sky relative to the
new-fangled magnetic compass “..for the needle moveth not”!