Historical divergence

From ancient times until the 17th century, astrologers constantly desired more accurate astronomical tables, and for this reason, they instigated and even funded many important developments in astronomy. The role of astrology as an important motivation for astronomical research diminished as the works of Galileo and others solved the problems in celestial mechanics that were of interest to astrologers, and as belief in astrological influences or correlations became extinct among astronomers. The needs of modern navigation and physics became more important motivators for astronomical research.

Astrology and astronomy began to take divergent paths during the rise of the rational and the scientific method in the Western World. The science of astronomy as we know it today (mathematical, mechanical, empirical) is of relatively recent origin. This discipline became separated from and generally antagonistic towards astrology only beginning around the time of the "Great Astronomers" -- Galileo, Kepler, Copernicus, Brahe, etc. (though they were all still astrologers as well as astronomers). This period is defined as the beginning of the scientific revolution, leading on into The Age of Enlightenment, sometimes referred to as The Age of Reason -- as stated, the two fields diverged completely in the West between approximately 1750-1800.

It is a commonly held belief among astrologers that Isaac Newton had an interest in astrology. However, Newton's writings fail to mention the subject and the handful of books in his possession that contained references to astrology were primarily concerned with other subjects such as the writings of Hermes Trismegistus (and mentioned astrology only in passing.) In an interview with John Conduitt, Newton said that as a young student, he had read a book on astrology, and was "soon convinced of the vanity & emptiness of the pretended science of Judicial astrology" (D.T. Whiteside, M.A. Hoskin & A. Prag (eds.), The Mathematical Papers of Isaac Newton (Cambridge University Press, Cambridge, 1967), vol. 1, pp. 15-19).

Perhaps the words astrolomer/astrolomy or astronoger/astronogy would be sufficient to describe the aforementioned dual roles of just about every person seriously studying (astronomy) and interpreting (astrology) the sky from antiquity until about 1750-1800. In Medieval Europe the word Astronomia was often used to encompass both disciplines as this included the study of astronomy and astrology jointly and without a real distinction; this was one of the original Seven Liberal Arts.

Astrology and astronomy stayed together for a very long time - the funding from astrology supported major astronomical research, which was in turn used to make more and more accurate ephemerides for use in astrology. As the funding and technology progressively increased, this inexorably lead to greater and greater discoveries that eventually drove the two apart.

Most of the very early, ancient astronomers/astrologers up until about 1750-1800 were simultaneously employed as astrologers for the powerful and the wealthy; many Kings and Queens employed court astrologers to aid them in the running of their kingdom, and this is where most of the money that was used to fund much need astronomical research came from.

University medical students were taught astronomy/astrology for use during their practice as physicians; they needed to know how to observe (astronomically) in order to be able to interpret (astrologically) and treat the illness. (See Medical astrology.)

More often than not it was only because of the prospect of getting better and more accurate astrological predictions that the rich (Royalty) were willing to invest in the very expensive projects of creating observatories and funding constant astronomical observations (see Tycho Brahe), which were very time consuming and just didn't seem quite as interesting as the 'mystical' art of astrology.