A long-lost star list has been discovered on the pages of a medieval manuscript by researchers. The erased text, copied in the 5th or 6th century AD, contains portions from the work of Hipparchus, the ancient Greek astronomer.

“These are the first known excerpts to come directly from Hipparchus’s star catalog. They illustrate the precision of Hipparchus’s measurements,” says Victor Gysembergh, a French National Centre for Scientific Research (CNRS) research professor and one of the authors of the paper, published in the Journal for the History of Astronomy.

The concealed text provides the coordinates of the constellation Corona Borealis, defining its stars' positions in the sky, as well as the constellation's overall length and breadth. Although Hipparchus is not named in the text, the positions of the stars correspond to measurements made approximately in 129BC, when the famed Greek astronomer lived.

The discovery is remarkable because Hipparchus' work has virtually gone, with his star catalog only known through later authors' writings.

“Ancient authors gave such puzzling indications that the very existence of Hipparchus’s star catalog was open to question,” Gysembergh says.

“None of its content was thought to have survived to the present day. It is the first time that we are able to read some of its content, thus confirming its existence and providing unprecedented insights into the ‘observatories’ of Hipparchus and his successor Claudius Ptolemy.”

Researchers uncovered the fragment from Hipparchus' lost book while studying the Codex Climaci Rescriptus, a manuscript from the 9th or 10th century AD. Scribes repurposed previous parchment pages to construct this codex, erasing its original content but leaving the earlier text visible beneath the words—documents reused in this manner are known as palimpsests.

Multispectral photography was utilized by experts to improve these weak fragments and uncover the Greek text.

The codex was initially stored in Egypt's Sinai Peninsula at Saint Catherine's Monastery. The majority of its pages were sold between 1895 and 1906 and traveled through several hands before arriving at the Museum of the Bible in Washington, DC. One sheet wound up in Birmingham, England, while others are still in Sinai.

“It is truly awesome to be part of such a discovery, which was made possible by teamwork with remarkable colleagues from fields as far apart as engineering, computer science, and paleography,” Gysembergh says.

“It sends shivers down my spine to think of all the other texts that are waiting to be discovered in other palimpsests.”