Copernicus and Astrology
Copernicus too lived in an age when astronomy and astrology were inextricably connected. Astronomy was generally seen as a theoretical underpinning of astrology, problems and events in the one, having serious implications for the other. Both areas, however, seemed to be far from perfect. At Cracow, Copernicus learnt astrology as well as astronomy. He studied the Alfonsine Tables, read the works of Peurbach and Regiomontanus, who, inspired by ancient astronomy, sought to reform theoretical astronomy, fully aware that improvement in astronomy would lead to improvement in its practice, astrology. One of his teachers at Cracow, John of Gogów, wrote on the astrological consequences of a planetary conjunction. The University of Bologna, since 1404, required its professor of mathematics and astrology to issue annual prognostications. Thus Domenico Maria issued prognostications, which gave for the following year the date of Easter, phases of the moon, weather forecasts, times of eclipses (if any), various auspicious and ominous dates, and general predictions for the year. Copernicus thus lived in a time when astronomical events were impregnated with astrological meanings.
He was equally aware of criticisms of astrology, such as the famous attack in Giovanni Pico della Mirandola's Disputations against Divinatory Astrology (Disputationes adversus Astrologiam Divinatricem, 1496). In book X, chapter 4, of this work Pico pointed out that ancients and moderns disagreed over the ordering of Mercury and Venus, which suggested that the basis for gauging planetary influences was shaky. Copernicus settled the ordering of planets in the De Revolutionibus (book I, chapter 10). By 1535, Copernicus had an established reputation for his accurate computations, and his almanac prepared for 1536 was circulating as the best one available. Reforms in astronomy implied improvement in astrology, and some contemporaries looked to the De Revolutionibus with that result in mind. So in 1541, Reiner Gemma Frisius (1508-55) wrote how the De Revolutionibus was an eagerly awaited work from a skilled mathematician which would hopefully end the astronomical errors and uncertainties that beset the astrologer. For others, the attraction of the book lay in its tables, which in turn had astrological implications.