This article examines a set of letters and observational reports that passed between Ludwig of Württemberg and Wilhelm of Hesse in response to the nova of 1572. Discussing the terminology used in this debate, it demonstrates that the terms “star” and “comet” were not unambiguous for sixteenth-century authors. A consideration of the relationship between accuracy of observation and the accuracy of the conclusions drawn from them, judged in the terms of twentieth-century astronomy, shows that those observers with the best instruments (...) did not always have the best understanding of what they had observed. Finally, the role played by theology in facilitating interpretations that did not accord with Aristotelian physics is highlighted. (shrink)