Over the course of Trinity Term 2020, the library staff at St. John's College will be taking you on a 'tour' of some of their favourites among our special collections. Every Monday, we will upload a new note on the item of the week. Read on to discover more about our chosen items..
Measuring the Heavens:
Johan Bayer’s Uranometria Ominum Asterismorum
Leona Stewart, Project Library Assistant
With the full title ‘Uranometria omnium asterismorum continens schemata, no a methodo delineata, aeris laminis expressa’, or translated, ‘Uranometria, containing charts of all the constellations, drawn by a new method, engraved on copper plates’, this seminal astronomical work which focusses on cataloguing stars was produced in Augsburg in 1603, by lawyer and amateur astronomer Johan Bayer.
Johan Bayer was born in Rain, Bavaria in 1572, and began a philosophy degree with the University of Ingolstadt at the age of twenty. Although he then went on to become the legal adviser to the city of Augsburg, like many of his peers at the time he had a particular passion for astronomy, and is best known for producing this celestial atlas, commonly referred to simply as Uranometria.
The word ‘uranometria’ derives from the Ancient Greek term οὐρανός (urano) meaning “heaven” and μέτρον (métron) meaning “something used to measure”, thus this expression literally translates to “Measurement of the Heavens”, and describes a chart or catalogue of celestial objects, particularly constellations of stars.
The striking title page of Bayer’s Uranometria [above] shows a busy architectural sculpture, with the title of the work affixed to it, flanked by Atlas on the left, Hercules on the right, and Greek divine figures Apollo, Cybelle and Diana above. The inscriptions describe Atlas as the earliest teacher, and Hercules as the earliest student, of astronomy. At the bottom of the title page, under the illustration of Capricorn, is a depiction of the city of Augsburg, where the catalogue was produced and where Johan Bayer spent most of his adult life.
This stellar atlas consists of 51 star charts which portray 60 constellations. Within this grand total exist 48 Ptolemaic constellations following the Almagest (each to their own double spread) and 12 brand new constellations which outlined the stars that could be seen from the southern hemisphere (all contained on one spread). Bayer himself made up the names for these new constellations. The work ends with two planispheres, which respectively overview the celestial details of the northern and southern hemispheres.
The construction of this atlas marked a significant change in the nomenclature of uranology, as Bayer was the first to use Greek letters to identify stars in a constellation. Generally ordered by brightness, this Greek letter would be followed by the genitive form of the Latin name of the constellation. For example, the brightest star in the Ptolemaic constellation Taurus is called Alpha (α) Tauri, which can be seen on the eye of the Taurus bull below.
This has been a widely used system since its formation in 1603, and is still used today to track celestial objects that can be seen with the naked eye. However, the invention of the telescope in 1608 allowed for a huge range of previously undiscovered stars to be found, and this nomenclature was deemed inadequate for the vast discoveries in the field of astronomy.
Each grid accurately determines the position of the stars to fractions of a degree, and are overlain with large images of the subject of the constellation. The charts were engraved on copper plates by Alexander Mair (1562-1617), and for unknown reasons, many of the human constellations are engraved as figures from behind, as opposed to facing the earth as was traditional. This quirk initially lead to confusion over the exact location of some of the celestial objects. Printed on the back of each of the engravings are lists of the stars included in the constellation with the Ptolemaic number, the Greek letter from Bayer’s nomenclature and position within the map, as well as discussions regarding the naming of the constellations.
A primary source of data used by Bayer came from Tycho Brahe’s Astronomiae instrauratae mechanica, which, although unpublished at the time of Bayer’s work, circulated in manuscript form and consisted of a dataset of unparalleled size. Brahe’s work was eventually published by Kepler in 1627. However, the Uranometria lists over 1,200 bodies, which is more than Brahe ever recorded, indicating that Bayer had taken data from multiple other sources.
Until his death in 1625, Bayer continued his work in astronomy, but did not publish alone again. He did, however, offer his knowledge to his friend and colleague Julius Schiller, who produced a new celestial atlas in 1627 entitled Coelum Stellatum Christianum. This new atlas provided a Christian interpretation of the stars, replacing zodiacal signs with the twelve apostles, and other constellations with religious imagery. The images below show Johan Bayer’s adaptation of the constellation Argo Navis, portrayed by the Ship of the Argonauts [left], and Julius Schiller’s variation, depicted by Noah’s Ark [right].
Augustyn, A. et al. (2016). Johann Bayer: German Astronomer. In: Encyclopedia Britannica. Retrieved May 27, 2020 from: https://www.britannica.com/biography/Johann-Bayer
Neri, D. (2016). Bayer, Johann. In: Biographical Encyclopedia of Astronomers (2016 ed.) New York: Springer.
Some information about the Uranometria came from a previous exhibition held at St John’s Library: Revolutions, curated by former College Librarian, Stewart Tiley.