I suppose I have always heard, read and assumed that the science of astronomy grew out of the pseudo-scientific practice of astrology. Well, maybe not so. I translate from a German study of the history of Mithraism first published in 1984.
The Stoic school, however, proceeded somewhat differently [from Plato’s proposal that the planets were self-willed and self-moving gods]: the logos (“thought”) governs the entire cosmos, within which there is harmony that regulates its parts. On Earth, the sun determines the alternation of the seasons, and the moon influences the female cycle; in the early 1st century BCE, the Stoic philosopher Posidonius of Apamea in Syria observed that the moon also caused the tides. Since the two great celestial bodies induced such effects, it was hypothesized that the planets Mercury, Venus, Mars, Jupiter, and Saturn also influenced human existence. Observations were collected regarding the connection between zodiacal constellations and human fate, initially with the legitimate intention of verifying a scientific hypothesis based on observed facts (a false hypothesis, but this was not known a priori). This led to the development of a vast astrological system, within which analogies and coincidences continued to be considered as probative elements.
(Merkelbach, Mithras 65 — translation from the Italian edition and compared with the German original)
Put like that, the claims of astrology become an entirely reasonable hypothesis. At least it seems very reasonable given a pre-Newtonian understanding of the universe. Unfortunately the testing that verified it for many was and has remained circular.
Another assumption I have long kept within arms reach is that a precise knowledge of regular planetary movements long preceded the Stoics. It was, I understand, a child of Babylonia. According to my Merkebach text however, that is another erroneous assumption long since superseded. I hope anyone who has a more up to date knowledge of the scholarly research into this question can correct me if needed.
During Plato’s time, an important astronomical discovery occurred. The planets—the Greek word means “wandering stars”—had always been considered celestial bodies that, unlike the others, wandered aimlessly. But Philip of Opuntius, a member of the Platonic Academy, observed that the planets moved “around the Earth” with regular revolutions.* They were not “wandering stars” after all, and law and order reigned in the heavens. Why did the planets follow regular, albeit complex, trajectories, the understanding of which would await the discoveries of Kepler and Newton? An unprovable hypothesis was formulated, which nevertheless seemed convincing: the stars were animated and followed regular orbits by their own will and judgment, as they were “visible gods.”
* It is not clear whether the regularity of the revolution of the planets was observed first in Greece or in Babylon. It was once assumed that, since ancient times, the Babylonians had precise knowledge in this field, but this hypothesis has proven to be unfounded.
(Translation of Merkelbach 65)
Merkelbach, Reinhold. Mithras. Konigstein/Ts : Hain, 1984. http://archive.org/details/mithras0000merk.
Merkelbach, Reinhold. Mitra. Il Signore Delle Grotte. Translated by P. Massondo. 2nd ed. ECIG, 1998.