Early Astronomy in the University of Michigan Collections
Western Astronomy: Introduction
In this exhibit, the phrase “western astronomy” broadly refers to the study, practice, and transmission of astronomy throughout medieval and early modern Europe as evidenced in a selection of books printed from the fifteenth to the seventeenth centuries. This selection devotes particular attention to the sixteenth and seventeenth centuries, a period often described as having undergone a “scientific revolution.”
In medieval Europe, knowledge of astronomy was transmitted in the Latin language. A translation of Ptolemy’s Almagest was made in Sicily around 1160 under the guidance of Henricus Aristippus, archdeacon of Catania. However, the most widely circulated translation of the Almagest was undertaken by Gerard of Cremona from the Arabic in Toledo in 1175. Essentially, the Ptolemaic system is a geocentric cosmology, placing the Earth as a motionless spherical body at the center of the universe, with the other heavenly bodies, the Sun, Moon, planets (Mercury, Venus, Mars, Jupiter, Saturn) and fixed stars, circulating around it. Ptolemy explains the motion of heavenly bodies with the theory that they are attached to rotating hollow spheres or orbs. In other words, an object attached to the equator of an orb would be carried around in a circle. Planets were embedded in the outer periphery of small spinning spheres, carrying them in circles corresponding to their epicycles. Moreover, these small spheres were embedded in a larger orb in a motion matching the eccentric circle. These orbs were nested inside one another as the illuminations in medieval manuscripts and, later on, the woodcuts and engravings in early printed books, consistently show. The largest of these orbs was the celestial sphere, which contained the stars and, at a distance of 20,000 times Earth’s radius, was the limit of the Ptolemaic universe. Nevertheless, the text of the Almagest was too complex for the actual needs of the curricula at European universities from the thirteenth century onward. Thus, brief textbooks containing basic astronomical knowledge were introduced, including Johannes de Sacrobosco’s De sphaera mundi (On the Sphere of the World), and the anonymous Theorica planetarum (The Theory of the Planets). These concise summaries of the corpus of Greek astronomy also contained important contributions from Arabic scholars, who, from the ninth century onward, translated, commented on, and added original findings to the works of Greek astronomers. Moreover, the practice of medieval astronomy was also shaped by the use of astronomical tables: they were mathematical tools designed to predict the positions of planets, lunar phases, eclipses, the times of the setting and rising of the sun, and the conjunctions of celestial bodies.
While medieval astronomers like Sacrobosco were still widely read in European universities well into the seventeenth century, the publication of Nicolaus Copernicus’ De Revolutionibus orbium coelestium libri sex (Six Books on the Revolutions of the Celestial Spheres) in Nuremberg in 1543 initiated a process of profound revision of the basic tenets of medieval astronomy. Copernicus’ heliocentric concept of the universe would be gradually endorsed by successive astronomers and mathematicians, especially through the works of Johannes Kepler and Galileo Galilei.
In 1939, the French historian Alexander Koyré coined the phrase “scientific revolution” to describe a period of extraordinary scientific developments in Europe throughout the sixteenth and seventeenth centuries. Subsequently, and oddly, numerous scholars have spent much ink to challenge the existence of such a revolution, mostly arguing that there was never any dramatic change caused by cataclysmic events of the sort that we associate with historical episodes such as the French revolution. Admittedly, it all depends on how we conceive the term “revolution.” For instance, we can define the word “revolution” as a set of long-term changes, in this case the gradual reception of new ideas that were massively disseminated by the printing press all over Europe. As Owen Gingerich convincingly argued in his landmark publication, An Annotated Census of Copernicus’ De revolutionibus, both the first and second editions of this work were avidly read by European astronomers. For instance, our copy of the De Revolutionibus belongs to a group of nine extant copies of the first edition containing marginalia derived from the notes by Jofrancus Offusius, a Rhenish astronomer working in Paris in the 1550s. Moreover, the fact that the Church took several decades before censoring Copernicus’ treatise, issuing a set of ten emendations in 1620, does not mean that the book was not read. One of the most remarkable readers of Copernicus’ treatise was Galileo Galilei, who following his telescopic observations of the Moon and the satellites of Jupiter in January 1610, published the interpretation of these observations in a 60-page booklet in that same year: Sidereus Nuncius (The Starry Messenger). Indeed, this publication paved the way to future debates on the validity of Copernicus’ theory, ultimately causing Galileo’s condemnation by the Church in 1633.
In this section, we have examined medieval and early modern astronomy through the lives and careers of outstanding individuals. Appropriately, Johannes Kepler also shared this approach as it is illustrated in the engraved frontispiece opening the Tabulae Rudolphinae (Rudolphine Tables). This extraordinary illustration summarizes the history of astronomy by depicting its most illustrious practitioners, from the Greek astronomers up to Kepler himself.