Fragments of ancient Greek astronomer Hipparchus’s long-lost Star Catalogue – believed to be the earliest known attempt to map the stars – have been discovered, hidden in a medieval manuscript.
Written between 170 and 120 BC, this treatise was previously known only through the writings of another ancient astronomer, Claudius Ptolemy, whose own catalogue was composed nearly 400 years after Hipparchus.
The fragments were identified in the Codex Climaci Rescriptus, a palimpsest composed of 146 folios taken from a 5th or 6th-century manuscript, which came from the monastery of Saint Catherine in Sinai, Egypt. Most of the folios are now in the collection of the Museum of the Bible in Washington DC.
The original Greek text had been erased sometime in the 9th or 10th century from the folios, which were then reused to write Syriac translations of works by the Christian monk John Climacus.
While examining some of the folios as part of a summer assignment, Jamie Klair (then an undergraduate student at Cambridge University) noticed traces of text relating to astronomy that had been erased.
The pages were then analysed in 2017 by a team of researchers from the Early Manuscripts Electronic Library in California and the University of Rochester using multispectral imaging – a technique that involves measuring the light reflected by an object at various wavelengths.
This revealed text from the 3rd-century poem Phaenomena about the constellations, as well as Eratosthenes’s myths about the origins of stars.
The most significant discovery, however, was that of a passage detailing the coordinates of the constellation Corona Borealis, establishing its stars’ positions in the sky, translated by a team of researchers from the French National Centre for Scientific Research, Sorbonne University, and Cambridge University.
The positions reflect observations that would have been made around 129 BC (when Hipparchus was active) and supports the ancient sources naming Hipparchus as the first person to map the stars.
Additionally, the research disproves the widespread belief that Claudius Ptolemy’s Star Catalogue was based solely on data from Hipparchus’ treatise, as the observations of the stars are different. It is more likely that Ptolemy combined Hipparchus’ observations with his own and perhaps also those of other authors.
Hipparchus’ coordinates have also been verified as having had an accuracy within one degree of their true positions, making his Star Catalogue significantly more accurate than Claudius Ptolemy’s.
This discovery illustrates the potential power of multispectral imaging in identifying and saving many more lost texts from oblivion.
The full findings have been published in the Journal for the History of Astronomy.