C S Lewis’s The Discarded Image gives a good presentation of the medieval model of the universe. Lewis warns us of the danger “chronological snobbery”- the idea that an idea is of our ancestors were stupid, and our ideas and beliefs are automatically superior simply because they are more recent. If astrology was such a widely accepted idea, we need to ask why rather than just put it down to ignorance.
People have always been able to see that the sun and moon affect what happens on the Earth below, bringing day and night, time and tide, summer and winter. It wasn’t irrational or stupid to draw the mistaken conclusion that the other celestial bodies also influence what happens here below.
You could argue that it’s no more irrational to believe that your actions are controlled by the movement of incredibly distant celestial objects than it is to believe that your actions are controlled by the movement of incredibly tiny atomic particles. Both are over-eager extrapolations from observable cause-and-effect phenomena. Astrology is just another flavour of determinism, and isn’t in some ways that far removed from modern “scientific” determinism. Will determinism one day be looked back on with the same scorn with which we now regard astrology?