into the seventeenth century, astronomy and astrology constituted a compound subject, called “the science of the stars.” Each part of this disciplinary couple could be further subdivided into theoretical and practical parts. Authors who contributed to the literature of the heavens described themselves with various names that might look familiar but which no longer carry currently specialized meanings, such as “mathematician” or “physician and astronomer.” Westman uses “astronomer-astrologer,” first coined by Gérard Simon (Kepler astronome astrologue, Paris, 1979) and also his own term, “heavenly practitioner”—terms of reference intended to be consistent with the historical agents’ own self-designations. Similarly, he contends that historical actors located the topic of planetary order within the domains of theoretical astronomy and theoretical astrology—as opposed to their practical counterparts. 2. Copernicus’s initial turn to the heliocentric planetary arrangement occurred in the context of his encounter with Pico della Mirandola’s wide-ranging attack on the science of the stars and, in particular, Pico’s contention that astrologers did not agree about the order of the planets (Disputationes adversus astrologiam divinatricem [Bologna: Benedictus Hectoris, 1496]). Copernicus was especially bothered by the uncertain ordering of Venus and Mercury. However, like Johannes Regiomontanus’s Epitome of Ptolemy’s Almagest (Venice, 1496), which was an important model for Copernicus, De revolutionibus (Nuremberg, 1543), astrology is nowhere mentioned in either work. 3. The controversy about the principles of astrological prognostication persisted as a major motive that drove debates about the heavens from the late fifteenth- to the early seventeenth century. Those debates took place within a nexus of political-cultural arrangements defined by the churches (both Catholic and Protestant), the universities and the royal, princely and imperial courts. At mid-sixteenth century Wittenberg, the Lutheran reformer university rector, Philipp Melanchthon (1497-1560), advocated a theology that stressed divine presence in nature and prophetic or prognosticative activity as a natural, inborn human desire to know God’s works. Astronomer-astrologers at Wittenberg, most notably Erasmus Reinhold (1511-1553) and his many students, read De revolutionibus selectively, ignoring the re-ordering of the planets and, instead, extracted from Copernicus’s work those calculational models that could be geometrically transformed into the framework of a stationary earth. Superficially, this “Wittenberg Interpretation” has sometimes been taken to refer to the methodological view known as “instrumentalism”—that scientific theories are just useful instruments of prediction—but Reinhold retained a “realist” view with respect to the solid spheres that carried the planets. 4. In the face of Pico’s critique there were different