Astrology in the Middle Ages was considered a branch of the magical arts, one informed by Jewish and Muslim scientific knowledge in Muslim Spain. As such it was deeply troubling to some Church authorities. Using the stars and planets to divine the future ran counter to the orthodox Christian notion that human beings have free will, and some clerical authorities argued that it almost certainly entailed the summoning of spiritual forces considered diabolical. We know that occult beliefs and practices became widespread in the later Middle Ages, but there is much about the phenomenon that we...