Seven parameters were necessary, five of which were independent for each planet. Knowing these parameters and the geometry of the model, it was possible to find the celestial longitude of any planet.
In the Almagest, Ptolemy showed how to construct tables that made this procedure much more tractable. The initial starting position, or radix, for each celestial body was determined for some fixed time and displayed in tabular form. The mean motion of each body was then derived from the underlying theory and tabulated. In addition, tables of correction factors were provided. Also included were specialized tables for conjunctions of the Sun and Moon, eclipses, parallaxes, and other phenomena.
The procedure for using the tables was straightforward. To find the location of a planet at some time in the future, the mean motion tables were used in conjunction with the planet's radix to calculate how far it had moved from its initial position. However, this only indicated the approximate location of the planet. Since the motions of the Sun, Moon, and planets are not uniform, a series of corrections was necessary to fix the position more accurately. In the case of a planet, retrograde motion needed to be accounted for.
This is a free page. This page contains 191 words. This
article contains 1,751 words (approx. 6 pages at 300
words per page).
Read the rest of this Article with our Astronomical Tables: Applications and Improvements During the Middle Ages Access Pass.
