This series starts with a first post.
Ch. 5. The Heavens
B. Their Operations
"The statement that the medieval Church frowned upon this discipline [of astrology] is often taken in a sense that makes it untrue. Orthodox theologians could accept the theory that the planets had an effect on events and on psychology, and, much more, on plants and minerals." p. 103.
What, then, did the church fight against? To paraphrase: three things: a. lucrative but misleading "predictive" astrology, b. astrological determinism and c. anything that looked like the worship of heavenly bodies. He then goes into a wonderful description of the qualities possessed and, thereby, imparted, by each of the seven planets. He, unfortunately, does not do the same for the signs of the zodiac, etc., much to our loss!
Astrology was merely the acceptance that such great realities as the stars and the planets must have an influence on lesser bodies like our own. The lesser the reality the greater the influence, so, especially on minerals such as gems and the like (gold is the product of the sun "influencing" underground mineral deposits, etc.), then plants, the minds of unwise people and especially on mass societal events (guided, as usual, by the minds of many unwise people).
This influence creates a certain character that "harmonizes" with the character of the influencing planet. But it does not say what this character will produce or what choices in must make. Therefore, then as now, making predictions based upon astrology of particular concrete human decisions was and is frowned upon by the church as entirely misleading. The influence is obvious and "scientific." The power of prediction is a farce. This is in large part because the church ruled out determinism. And, of course, anything that smacked of idolatry.
Again, Lewis' way of reminding us our own western heritage about this stuff, especially the "influences" I think provides just excellent resources for imagining "magic" in fantasy settings. The central principle of alchemy, found on the Emerald Tablet, is "as above, so below." This could be used to truly interesting results with dungeon design. Imagine a dungeon of 9 levels, each deeper one corresponding to an ever higher heavenly sphere that "influenced" it. Going down, silver, quicksilver, copper, gold iron, tin, lead, gems, etc. Fun!