Christoph Rothmann wrote a treatise on the comet of 1585 shortly after it disappeared. Though it was not printed until 1619, Rothman sent a copy of his treatise in 1586 to Tycho Brahe, decisively influencing the latter's rejection of solid celestial spheres two years later. In his treatise, Rothmann joined the elimination of the solid celestial spheres to his concept of air as the substance filling the cosmos. He based his argument on the absence of refraction and the celestial location of the comet. The treatise also contained clear statements reflecting Rothmann’s adoption of Copernicanism. This first critical edition of the treatise is accompanied by an English translation and a thorough commentary. Some appendices with archival documents illustrate the genesis of Rothmann’s treatise.

Table of Contents:
Preface xi Miguel A. Granada Introduction 1 Miguel A. Granada 1 Christoph Rothmann and Astronomy in Wittenberg 1 2 Astronomy in Kassel: Landgrave Wilhelm IV and His Programme of Stellar Astronomy 19 3 The Comet of 1585 and the Dialexis cometae 24 4 Phases of Composition of the Dialexis cometae 30 5 Rothmann’s Cosmological Innovations in the Dialexis cometae 36 6 The Status of Astronomical Hypotheses 55 7 The Title of the Work 64 2 Dialexis Cometae qui Anno Christi M.D.LXXXV. mensibus Octobri et Novembri apparuit 67 Latin text prepared by Miguel A. Granada A Discourse on the Comet Which Appeared in the Months of October and November of 1585 67 Translation by Nicholas Jardine and Adam Mosley, with annotations by Miguel A. Granada, Nicholas Jardine and Adam Mosley Chapter 1. On the Observations of This Comet 78 Chapter 2. Concerning the Motion of This Comet in Longitude and Latitude 92 Chapter 3. Whether This Comet Had Parallax 104 Chapter 4. In Which Sphere This Comet Was 114 Chapter 5. Since It Is Commonly Believed That the Spheres of the Planets Are Solid Bodies, How Could the Comet Have Progressed in Them? And What Is to Be Thought on This Question? 120 Chapter 6. A Refutation of Some Opinions Concerning Comets; Namely, That They Are Neither Species Appearing without Matter, Nor Perpetual Bodies Together with the Rest of the Stars, Nor Vapours Ignited in the Air 146 Chapter 7. The Opinion of the Author about the Matter and Essence of Comets 164 Chapter 8. The Uses of the Examination of Comets 178 Chapter 9. That That Matter Flowing around the Planets Differs Not at All from Pure Sublunar Air, and Where, Moreover, the Contrary Arguments Are Refuted 186 Description of the Comet Which Shone in the Year 1596 in the Month of July, but Set Out in a Fuller Form from the Papers of the Same Rothmann 202 3 Appendices: Related Texts and Translations 207 Miguel A. Granada, Nicholas Jardine and Adam Mosley 1 Letters of Christoph Rothmann to Landgrave Wilhelm IV of Hesse-Kassel, 1585–1586 208 2 Letter of Wilhelm IV of Hesse-Kassel to Heinrich Rantzau, 20 October 1585 246 3 Letter of Wilhelm IV to Christoph Rothmann of 18 November 1585, Authorising the Drafting of a scriptum on the Comet 250 4 Elias Olsen Morsing’s Account of the Comet of 1585 252 4 How to Present a Copernican Comet: The Form and Tactics of Christoph Rothmann’s Dialexis on the Comet of 1585 258 Nicholas Jardine 1 Introduction 258 2 Disciplines: Mathematics vs. Philosophy 260 3 Disciplines: Theology 262 4 Genres: Dialexis, ‘Critical Doxography’, Historia, Observationes 267 5 Persuasive Tactics 273 6 Comets as Boundary Objects 280 5 The History and Historiography of Early Modern Comets 282 Adam Mosley 1 1577 and All That: What Every Historian of Astronomy Knows 282 2 Historia: Comets, Astronomy, and Historical Astrology 287 3 1577 and All That Revisited 323 6 A Brief Note on Cometary Parallax 326 Adam Mosley 1 Tycho, Regiomontanus, and the Problems of Parallax 326 2 Rothmann and the Parallax of the Comet of 1585 334 3 Conclusion 339 Bibliography 341 Index of Persons 367 Index of Places 373 Index of Subjects 374