The Jesuit Sunspot Book That Was Half a Major Astronomical Treatise and Half a Sustained Attack on Galileo

Christoph Scheiner (1573–1650) was a senior German Jesuit mathematician and astronomer. He held the mathematics chair at the Jesuit University of Ingolstadt from 1610, was professionally close to the senior Jesuit astronomer Christoph Grienberger at the Collegio Romano in Rome, and was substantively the most accomplished Jesuit astronomical observer of his generation. His telescope-design work in the 1610s produced the Keplerian telescope — the two-convex-lens configuration that has remained the basis of refracting astronomical telescopes for the four centuries since.

He was also the man who spent thirty years arguing with Galileo about who had discovered sunspots first.

The 1611 observations

Scheiner observed sunspots from the Ingolstadt observatory in March 1611, probably independently of Galileo’s roughly contemporaneous observations and of Harriot’s December 1610 English observations. His Jesuit superiors at Ingolstadt forbade him to publish under his own name (the substantial Aristotelian astronomical tradition that Catholic-Jesuit theology had taken substantively as authoritative ruled out the possibility of imperfections on the surface of the Sun); Scheiner instead arranged for the substantial Augsburg merchant-scholar Marcus Welser to publish his findings as a series of pseudonymous letters under the pen name Apelles latens post tabulam (‘Apelles hiding behind the picture’) in January 1612.

The substantial Apelles letters interpreted sunspots as small planet-like bodies orbiting the Sun at distance from its surface — a framework that preserved the Aristotelian-Jesuit doctrine of solar perfection by attributing the apparent spots to opaque bodies in front of the Sun rather than features on it. Galileo responded with his Lettere solari of March 1613, which substantively dismantled the Apelles interpretation on observational grounds (the spots’ motion, perspective changes, and lifetime patterns required them to be features of the solar surface itself) and substantively claimed personal priority for the original sunspot discovery.

The priority war

Scheiner accepted Galileo’s substantive observational arguments by approximately 1614 but never accepted the priority claim. He had observed sunspots in March 1611; Galileo had observed them in early 1612 by Galileo’s own published account (earlier in private, but Galileo had not published the earlier observations). Scheiner substantively considered himself the first published European observer of sunspots and substantively resented Galileo’s aggressive 1613 priority claim.

The twenty-year subsequent build-up produced Rosa Ursina sive Sol (‘The Bear-Rose, or the Sun’) — Scheiner’s Latin treatise on the Sun, published in installments between 1626 and 1630 at the printing press of his patron Paolo Orsini at Bracciano. The treatise ran to approximately 780 folio pages and was the most comprehensive astronomical treatment of the Sun published anywhere in Europe during the 17th century.

About half of the Rosa Ursina was primary astronomical content: detailed observational catalogues of sunspots from 1611 to 1625 (the most accurate pre-19th-century systematic record of solar activity, and valuable to modern reconstructions of solar minima including the Maunder Minimum of 1645–1715); a theoretical treatment of solar rotation; discussions of telescopic technique and instrument design.

The other half was a sustained attack on Galileo’s priority claim. The Galileo material was personal in tone, extensive in length (approximately 300 pages were devoted to detailed re-examination of the 1612–1613 priority correspondence), and damaging to subsequent Galileo-Jesuit institutional relations.

The Inquisition consequences

The Rosa Ursina was published in the same five-year period as Galileo’s Dialogue Concerning the Two Chief World Systems (1632). The two works substantively defined the Jesuit-Galilean dispute on the Copernican question through the substantive subsequent decade. Scheiner had substantively moved to Rome by the late 1620s and was involved (peripherally but not innocently) in the Jesuit institutional campaign that produced the 1633 Inquisition trial of Galileo. The 1633 condemnation substantively ended Galileo’s institutional position and produced his nine-year house arrest at Arcetri.

Scheiner himself was reassigned to a Jesuit teaching post at Neisse in Silesia in 1639 and died there in July 1650, aged 77.

The Rosa Ursina survived as a substantively useful astronomical source for two centuries afterwards. The dual character of the work — scientific contribution plus personal polemic — has troubled Jesuit-historiographic and Galileo-historiographic traditions ever since.