Question Seven of Chapter Nine of the Third Decade
Whether it is a sin to investigate stolen things by inspection of an astrolabe and by judgment of the stars
It is asked whether it is a sin to investigate things secretly taken away by inspection of an astrolabe and by judgment of the stars.
It is answered that it is not a sin to investigate certain things which properly follow upon a change in the stars—for example, heat and cold, rain and dryness.
To judge, however, concerning things which are subject to free choice and are not subject to the law of the stars is a grave sin, because an invocation of demons intervenes in such matters.
These things are from Alexander, Second Part of the Summa, question 92, article 5, question 3.