Hipparchus’ catalog of lost stars, considered the first known attempt to map the entire night sky, may have been discovered on a scroll preserved in the monastery of St. Catherine in Egypt’s Sinai Peninsula.
In 2012, a student of noted biblical scholar Peter Williams noticed something curious behind the letters of the Christian manuscript he was analyzing at Cambridge University.
The student, Jamie Klair, had come across a famous Greek passage often attributed to Eratosthenes; astronomer and chief librarian of the Library of Alexandria (one of the most prestigious places of learning in the ancient world).
In 2017, multispectral imaging of the document revealed nine sheets of pages containing hints of a text that had been written. It wasn’t an unusual find in itself: parchment was a valuable commodity centuries ago, so it wasn’t uncommon for scholars to scrape up old skins for reuse.
Looking at the results of the second year of the pandemic, Williams noticed some strange numbers in the folios of St. Catherine’s Monastery.
When he turned the page over to scientific historians in France, the researchers were stunned. Historian Victor Gysembergh of the French national center for scientific research CNRS in Paris told Jo Marchant in Nature that “it was immediately clear that we had star coordinates.”
Original text from the Monastery of Saint Catherine on top of faint traces discovered by multispectral imaging. (Museum of the Bible/Early Manuscripts Electronic Library/Lazarus Project/University of Rochester/multispectral processing by Keith T. Knox/tracings by Emanuel Zingg)
So how do we know who wrote those coordinates for?
The short answer is no, at least not with absolute certainty. What experts do know, however, is that the Greek astronomer, Hipparchus, was working on a star catalog of the western world sky between 162 and 127 BC.
Several historical texts refer to Hipparchus as “the father of astronomy” and credit him with the discovery of how the Earth “wobbles” on its axis in what is now known as precession. He is also said to have been the first to calculate the movements of the Sun and the Moon.
Looking at the star map buried behind the text of the St. Catherine’s Monastery scrolls, the researchers worked backwards to figure out the precession of the Earth at the time the map was written. The coordinates of the stars roughly coincided with the expected precession of our planet around 129 BC, during the lifetime of Hipparchus.
Until this map was found, the oldest known star catalog was compiled by the astronomer Claudius Ptolemy in the 2nd century AD, three centuries after Hipparchus.
The only other work left by Hipparchus is a commentary on an astronomical poem describing star constellations. Many of the coordinates that Hipparchus gave for the stars in his Commentary on the Phenomena closely match the St. Catherine’s Monastery document, although the fragmentary text can be difficult to decipher.
Readable coordinates of only one constellation, Corona Borealis, can be recovered from the folios of Egypt, but researchers believe it is likely that Hipparchus mapped the entire night sky at some point.
Without a telescope, this work would have been extremely difficult and time-consuming.
According to the researchers, the hidden passage reads like this:
“The aurora borealis, situated in the northern hemisphere, spans 9°¼ in longitude from the first degree of Scorpio to 10°¼8 in the same zodiacal sign (i.e., in Scorpius). In width it spans 6°¾ from 49° N. Pole to 55° ¾.
Within it, the star (β CrB) to the west next to the bright one (α CrB) leads (that is, it is the first to rise), standing in Scorpius 0.5°. The fourth star 9 (ι CrB) to the east of the bright one (α CrB) is the last (ie, rising) [. . .]10 49° from the north pole. The southernmost (δ CrB) is the third counting from the bright (α CrB) eastward, which is 55°¾ from the north pole.”
The notations match the ancient Greek terminology. The term “longitude” is based on the east-west extent of a constellation, while “latitude” describes the north-south extent of the constellation.
Compared to Ptolemy’s later work, Hipparchus’ mathematics appears to be much more reliable, within a degree of what modern astronomers would later find. This suggests that Ptolemy did not simply copy the work of Hipparchus.
Another manuscript, an eighth-century AD Latin translation of the Phaenomena, shares a similar structure and terminology to the Corona Borealis passage, suggesting that it is also based on the work of Hipparchus.
The constellations mapped in this document are Ursa Major, Ursa Minor, and Draco. Again, many of the star values match what is seen in the Hipparchus Commentary.
Some astronomers had previously suggested that Hipparchus wrote down the original coordinates cited in these Latin documents, but the discovery of this new text adds more weight to that idea.
“The new fragment makes it much, much clearer,” Mathieu Ossendrijver, a historian of astronomy at the Free University of Berlin, told Nature.
“This star catalog that has been hovering in the literature as something almost hypothetical has become very concrete.”
Researchers hope that in the future a more readable text can be recovered from the monastery’s documents.
The study was published in the Journal for the History of Astronomy.