Didascalicon, Book II: the sciences, their parts and their discipline
Chapter XI. On astronomy
Astronomy and astrology seem to differ in this, that astronomy took its name from the law of the stars, astrology is so called as discoursing about the stars. For nomos is interpreted law and logos speech. So astronomy seems to be that which treats of the law of the stars and the revolution of the heaven, investigating the regions, circles, courses, risings and settings of the stars, and why each is so called. Astrology, however, considers the stars according to the observation of birth and death and of any other events whatever; which is partly natural, partly superstitious. Natural, in the complexions of bodies, which vary according to the temperament of the higher bodies, as health, sickness, storm, fair weather, fertility and barrenness. Superstitious, in contingent matters and in those that lie under free will; this part the mathematicians treat.