Following my previous post about translating the medieval Latin astrologia, I found the article "Astrology" by Charles Burnett in Medieval Latin: an introduction and bibliographical guide (ed. Mantello and Rigg, here at Amazon).
It turns out that astronomia was also a term used in medieval Latin. Astronomia was the mathematical science that measured the position and movements of the heavenly bodies. Astrologia was a physical science based on the (not entirely incorrect) assumption that events on earth (such as tides, but also human characters and events) were influenced by the stars and planets. Isadore divides astrology into the 'natural' part - which concerns events such as tides and seasons - and 'superstitious' part, which concerns the prediction of human character and events.
To complicate matters, thirteenth century authors used the terms interchangeably. Bacon uses the term astrologia to signify astronomy, and astronomia to signify astrology. It is not clear which sense Thomas intends for astrologia in the passage I quoted in the previous post.