A team of researchers has successfully recovered part of the oldest known star catalog, attributed to the Greek astronomer Hipparchus, widely regarded as the father of astronomy.
This catalog, written between 170 and 120 BCE, had long been considered lost. The original manuscript was completely overwritten in the fifth century so the parchment could be reused. This type of recycled document is known as a palimpsest. At the time, parchment – made from animal skins – was both rare and expensive, so erasing and rewriting texts was common practice.
Using technology to unlock the past
This remarkable breakthrough was made possible thanks to the synchrotron at the SLAC National Accelerator Laboratory in Menlo Park, California. Operating in a similar way to the Large Hadron Collider, the machine emits extremely precise and powerful X rays. These rays can penetrate materials without damaging them and reveal chemical differences invisible to the naked eye.
By applying this technology, researchers at SLAC, led by archaeologist and translator Victor Gysembergh from Sorbonne University in Paris, were able to see through layers of ink and decipher text that had been erased centuries ago. Beneath the visible writing, they identified the original stellar coordinates recorded by Hipparchus. These had been covered by a Syriac translation of religious writings by Saint John Climacus of Sinai.
What had seemed permanently lost was simply hidden – waiting for the right technology to bring it back into view.
A clearer picture of ancient astronomy
Until now, this star catalog – consisting of eleven folios written on both sides and preserved within the Codex Climaci Rescriptus – was known only through the work of Claudius Ptolemy, another ancient astronomer who created his own catalog nearly three centuries later.
After an initial attempt at deciphering the manuscript in 2022, researchers turned to X ray fluorescence, which allowed them to uncover the equatorial coordinates of several stars, along with illustrations depicting constellations.
The data revealed something striking. Hipparchus, already known for inventing a stellar magnitude scale, observing planets, and making impressively accurate astronomical predictions, was mapping the sky with extraordinary precision. His measurements were accurate to within about one degree – all achieved through naked eye observation.
In fact, his recorded positions appear to be significantly more precise than those later documented by Ptolemy. That alone reshapes how historians view the development of astronomical knowledge in antiquity.
Why this discovery matters
This rediscovered star catalog does more than fill a historical gap. It sheds light on the methods of observation developed in the ancient world and deepens our understanding of how early astronomers studied the heavens without telescopes or modern instruments.
It also highlights how scientific knowledge can be transmitted, altered, or even lost over time. The manuscript survived physically, yet its original content disappeared beneath later writing for centuries. Without modern imaging tools, Hipparchus’ meticulous work might have remained hidden forever.
Above all, the discovery demonstrates the extraordinary potential of modern science to revive texts once believed erased beyond recovery. By combining archaeology, history, and advanced imaging technology, researchers have quite literally brought the ancient sky back into focus.
In doing so, they remind us that progress is not only about looking forward. Sometimes, it is about learning how to look more carefully at what the past has left behind – because even erased words can still have something important to say.
This looks like a slab of broken marble, but it is actually a calendar, and we still use pieces of it today. It told Romans which days were lucky and which ones to avoid. It is called the Fasti Praenestini, and it was written by Verrius Flaccus, private tutor to the grandsons of Emperor Augustus. It laid out the whole Roman year: the festivals, the religious holidays, and even which days were considered lucky and which ones to avoid for doing business. That is where the word comes from. Days marked F, dies fasti, were open for business and the law courts, while days marked N, nefasti, were forbidden. So it is basically the ancient Roman version of the calendar hanging on your wall, and the connection runs deeper than that. Our months are still the Roman months. July is named for Julius Caesar, and August for Augustus himself, the very emperor whose grandsons this calendar's author was hired to teach.
