In the last post, Ptolemy concluded that the motion of the fixed stars over time, known as precession, happens about the poles of the ecliptic. He determined this by stating that the longitude of stars with relation to the ecliptic remained consistent over a long interval of time but varied with respect to the celestial equator. That post concluded with Ptolemy’s promise that we would be able to determine rate of that precession using the same data he presented previously.
It is particularly [easy to demonstrate] from the differences in declination found for those stars near the equinoctial points.
Continue reading “Almagest Book VII: On the Rate of Precession from Hipparchus’ Observations”