Astrology leads to Astronomy
With this interest in the sky as an omen came the need for detailed recording and observation of the positions of the heavenly bodies. The more precise data allowed the ancients to derive the first rudimentary formulations of celestial mechanics, which allowed for better predictions. The art of astrology drove the need for a science of astronomy.
“Archaeological excavation confirms that early in the first millennium BC accurate knowledge existed of the Sun’s annual course, of the phases of the Moon and of the periodicities of certain planets.” (Encyclopedia Britannica p. 640)
The ability to predict planetary position based on calculations was the primary step that allowed astrology to be used as a universal tool for divination. Prior to this the astrologer was dependent on a clear sky for his forecasts. Prediction was the first step away from naturalist observation towards an increasingly heavy reliance on ephemerides, i.e. tables of planetary positions.
Astronomy elucidates the Astrological Symbols
Let it be stressed that in the study of the sky as a divine symbol that interpretation of the symbol can only go as far as the knowledge of the symbol itself. For this reason the technology of astronomy and the art of astrology have proceeded hand-in-hand. We see time and again changes in astronomical theory preceding an astrological innovation. This relationship is manifested most clearly in the case of Ptolemy, who was the foremost authority of his day in both astronomy and astrology.