Discovery of extracts from a lost astronomical catalog

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A leaflet from the Codex Climaci Rescriptus © Peter Malik
A leaflet from the Codex Climaci Rescriptus © Peter Malik

Hipparchus’ star catalog is the earliest known attempt to accurately determine the positions of fixed stars. Researchers have just found fragments of this missing text in an old manuscript. They show that Hipparchus’ data were significantly more accurate than those of another catalog composed centuries later.

Researchers from CNRS, Sorbonne University and Tyndale House affiliated to the University of Cambridge have just found fragments of the star catalog composed by the Greek astronomer Hipparchus during the 2nd century BC. These texts had been erased from a manuscript to reuse pages in the medieval period and could be uncovered using multispectral imaging technologies. The study of these extracts, published in the Journal for the History of Astronomy on October 18, 2022, sheds new light on astronomy in antiquity.

Old grimoires can contain coveted secrets, even by the most Cartesian minds. Like the fragments of an ancient astronomical treatise lost for centuries: the Hipparchus star catalog. Written between 170 and 120 BC by the Greek astronomer Hipparchus, it is the oldest known attempt in the history of mankind to accurately determine the positions of fixed stars by associating them with numerical coordinates.

This text was only known through the writings of Claudius Ptolemy, another ancient astronomer who composed his own catalog nearly 400 years after Hipparchus, until now. Researchers from the Leon Robin Center for Research on Ancient Thought (CNRS/Sorbonne University) and their British colleague from Tyndale House in Cambridge have just deciphered the descriptions of four constellations from Hipparchus’ star catalog.

This discovery comes from the Codex Climaci Rescriptus 1 , a work made up of parchments that were erased and reused to rewrite over, also known as a palimpsest. In the past, this Codex contained an astronomical poem in ancient Greek with, among the elements of commentary of this poem, fragments of the catalog of Hipparchus. This text, which was erased in medieval times, has been revealed thanks to multispectral imaging 2 performed on the palimpsest by theEarly Manuscripts Electronic Library and Lazarus Project team.

The fragments of the star catalog are the oldest known to date and bring major advances in its reconstruction. First of all, they refute a widespread idea that Claudius Ptolemy’s star catalog is only a "copy" of Hipparchus’, because the observations of the four constellations are different. Furthermore, Hipparchus’ data is verified to the nearest degree, which would make his catalog much more accurate than Ptolemy’s, even though it was composed several centuries earlier.

For the research team, this major discovery sheds new light on the history of astronomy in antiquity, and on the beginnings of the history of science. Above all, it also illustrates the power of advanced techniques, such as multispectral imaging, whose application to illegible palimpsests could save from oblivion disappeared texts of philosophy, medicine or horticulture.

1 The Codex Climaci Rescriptus is kept at the Museum of the Bible in Washington DC (USA) and probably comes from the monastery of Saint Catherine of Sinai (Egypt), one of the oldest monasteries in the world still in activity. It is composed of leaves from a Greek manuscript of the fifth or sixth century AD.

2 Multispectral imaging involves measuring the light reflected from an object at different wavelengths of the electromagnetic spectrum, using artificial lighting and high dynamic range sensors. The collected data are then processed by computer to extract relevant information, such as erased writing marks, and presented as images.

New Evidence for Hipparchus’ Star Catalogue Revealed by Multispectral Imaging. Victor Gysembergh, Peter J. Williams and Emanuel Zingg. Journal for the History of Astronomy, October 18, 2022. DOI:10.1177/00218286221128289