kinds of efforts to improve astrological prognostication during the sixteenth century and Copernicus’s proposal to reform theoretical astronomy was but one of them. 5. The appearance of unforeseen, singular, celestial novelties between 1572 and 1604 pushed a handful of astronomer-astrologers to consider whether alternative planetary orderings, including those of Copernicus, Tycho Brahe (1546-1601), Nicolaus Reimars Baer (1551-1600) and Paul Wittich (1546-1586) could better explain the unanticipated phenomena. 6. This consideration of alternatives was the first major instance of underdetermination in the history of science (where the same observational evidence equally supports two, logically different hypotheses), although the historical agents were unaware of the epistemological generality of that problem. It resulted in new kinds of controversies and raised unprecedented questions about weighting the criteria for adjudicating among different hypotheses, including ancient authority, scriptural compatibility, simplicity, explanatory breadth, predictive accuracy and physical coherence. 7. The second generation followers of Copernicus (Michael Maestlin [1550-1631], Thomas Digges [1546-1595], Giordano Bruno [1548-1600], Christopher Rothmann [ca. 1550-1600]) did not constitute a socially- and intellectually-unified movement. And the failure of the high-profile third-generation proponents Johannes Kepler (1571-1630) and Galileo Galilei (1564-1638) to forge a cooperative and productive alliance around their defense of the Copernican theory is a particularly notable instance of this larger pattern of disunity. 8. Shared social context underdetermined the adoption of new theoretical claims. Many Copernicans, for example, were attracted to court settings because those spaces were more open to novelty than traditional university settings. But while court patronage allowed for rhetorical and philosophical diversity, it fails to explain why particular figures, like Galileo, adopted specific theoretical claims, such as the Copernican hypothesis. 9. Galileo’s famous telescopic claims can be thought of as introducing the discovery of recurrent novelties into the debate about alternative hypotheses. Unlike novas and comets, which seemed to appear only when God wanted to send a message, a human being with an instrument could make phenomena like the moon’s rough surface, never-before-seen distant stars or Jupiter’s ‘planets’ appear and disappear. Success in convincing others of the reality of these phenomena occurred largely through print rather than by live demonstrations with the instrument. 10. The main social locus of change of belief was not some twentieth-century-like “scientific community,” but the master-disciple relationship that was rooted in the all-male-cultures of the universities and modeled on the paternalistic structures of the family. 11. The Copernican Question proposes a new periodization that argues for