A long-lost star map that is enormously important in the history of science has been discovered in the time-worn pages of a Medieval manuscript after a search that has spanned nearly 2,000 years, according to a new study.
Compiled by the ancient Greek astronomer Hipparchus, who lived during the 2nd century B.C., the legendary star catalog marks the first attempt to record accurate positions of celestial objects with fixed coordinates. Like many ancient documents, copies of the catalog were lost in the centuries after it was written, and it is only known from references to it in later works. The mystery of its disappearance has prompted a search for the catalog that dates back nearly 2,000 years.
Now, a team led by Victor Gysembergh, a professor at the French National Center for Scientific Research (CNRS), reports that passages of Hipparchus’ Star Catalog have been discovered underneath the text of a Christian manuscript that originated from Egypt’s Saint Catherine’s Monastery, and is now mostly housed at the Museum of the Bible in Washington, D.C.
The “new evidence is the most authoritative to date and allows major progress in the reconstruction of Hipparchus’ Star Catalog,” according to a study published on Tuesday in the Journal for the History of Astronomy.
“Hipparchus’ Star Catalog is the very first attempt in human history to precisely measure the positions of the fixed stars,” Gysembergh said in an email. “It is a major milestone in the birth of science as a collective endeavor to measure and predict our surroundings.”
Hipparchus’ original catalog documents the celestial longitude and latitudes of more than 800 stars, setting it apart from previous maps that did not use two coordinates. Although it has long been lost to history, researchers have surmised that it both existed and influenced later, more well-known astronomical texts.
“This discovery proves that Hipparchus, often considered the greatest astronomer of ancient Greece, really did map the heavens centuries before other known attempts,” Gysembergh noted. “To quote Mathieu Ossendrijver of the Free University in Berlin, ‘This star catalog that has been hovering in the literature as an almost hypothetical thing has become very concrete.’ It also illuminates a crucial moment in the birth of science, when astronomers shifted from simply describing the patterns they saw in the sky to measuring and predicting them.”
The story of how these passages of the fabled star map resurfaced seems lifted from the pages of a historical fantasy. The Medieval manuscript from the Egyptian monastery contains a Christian work called the Codex Climaci rescriptus that was written in an Aramaic dialect about 1,000 years ago. However, this codex is what’s known as a palimpsest, which means that older text had been scraped off so that the parchment could be reused.
Scientists have developed sophisticated imaging techniques that can peer into these palimpsests and decipher the layers of text that have been washed off over the centuries, almost like reading invisible ink. The approach has led to countless discoveries in recent years that involve everything from the work of Archimedes, to early Qur'anic writings, to ancient Roman texts.
In 2012, Peter Williams, a biblical expert and lecturer on Hebrew language at the University of Cambridge and a co-author of the new study, tasked his students with studying the Codex Climaci rescriptus for signs of interesting “undertext” that had been removed by Medieval scribes.
The project revealed hints of ancient Greek astronomical writings, but it wasn’t until years later, when the palimpsest was examined using multispectral imaging techniques, that the unprecedented value of the manuscript began to come into focus. While under lockdown due to the COVID-19 pandemic in 2020, Williams realized that the images contained a wealth of ancient astronomical information, which prompted him to alert Gysembergh.
“When Peter Williams contacted me about the astronomical measurements he had recently identified in the Codex Climaci rescriptus, I immediately became very excited because I understood that this document could finally provide firm ground to reconstruct Hipparchus’ star catalog,” Gysembergh said.
Gysembergh, Williams, and a third study co-author Emanuel Zingg, a researcher at Sorbonne University, confirmed that the passages are copies of Hipparchus’ Star Catalog. The team was also able to use this breakthrough to determine that another manuscript, called Aratus latinus, contains direct excerpts of the long-sought document, including coordinates for the constellations Draco, and Ursa Major and Minor, also known as the Big and Little Dippers.
“These catalog passages were copied as commentary material to Aratos’ Phaenomena, an astronomical poem that was quite famous in Antiquity,” Gysembergh explained. “The scholar(s) who composed the original commentary may have had access to an original text dating back to Hipparchus’ time; the scribes who later copied Codex Climaci rescriptus and the manuscripts of Aratus latinus were intent on reproducing the original commentary as faithfully as they could.”
Prior to this discovery, Claudius Ptolemy’s Almagest, written in the 2nd century A.D., was the earliest known example of this type of precise star catalog. Not only does the new study push back the record of these sophisticated charts by about 300 years, it also suggests that Hipparchus’ work was more accurate than its Ptolemaic successor.
“In a certain sense, scholars have been asking about this catalog for as long as they have been reading Claudius Ptolemy’s Almagest (nearly 2,000 years),” Gysembergh said. “The search certainly became more active with the appearance of the history of science as a rigorous academic endeavor in the 19th century.”
At last, this search for a lost map of the night sky, which has spanned dozens of generations, has come to fruition. But for Gysembergh and his colleagues, this journey into the past is far from over.
“Two years ago, I would never have hoped to witness such a discovery within my lifetime, let alone be a part of it,” Gysembergh said. “This makes me optimistic that more passages from the catalog will be recovered in the future. The first place to look is in Codex Climaci rescriptus itself, parts of which remain difficult to decipher. New methods in multispectral imaging may provide the key to reading more text. More generally, there are thousands of palimpsests and damaged manuscripts around the world that would benefit from multispectral imaging.”
“It is possible that original texts by Hipparchus survive somewhere in ancient parchments or papyri; among these, his Star catalog might resurface one day,” he concluded. “It is truly awesome that in the 21st century, new texts from great scientific and literary authors of Antiquity continue to be recovered.”