Hipparchus, the foremost Greek astronomer and a founding figure of astronomy, was centuries ahead of his time. More than 2,150 years ago, he calculated the wobble of Earth’s axis, devised a scale for stellar brightness and compiled the first known star catalogue — a work that was subsequently lost over the centuries.

Now, part of that missing legacy is coming back into view. Using a form of high-tech X-ray imaging, an international team of researchers has succeeded in reading fragments of the catalogue in a medieval palimpsest — parchment manuscripts that were erased and reused for newer texts.

The palimpsest was created at St Catherine’s Monastery in Sinai around the 5th or 6th century AD. Some pages are believed to have been erased and overwritten as many as six times over the following 200 years. In its present form, the manuscript is known as the Codex Climaci Rescriptus and contains a Syriac translation of the works of St John Climacus, a 6th–7th century monk.

The new study examined the palimpsest using the synchrotron at the SLAC National Accelerator Laboratory in California — a circular machine that accelerates electrons to nearly the speed of light. As the electrons are forced to change direction along the ring, they emit X-rays capable of revealing the internal structure of objects in remarkable detail.

The synchrotron was able to distinguish the hidden text because the older ink had left calcium deposits, unlike the newer writing on the parchment, which contained higher levels of iron. By calibrating the instrument accordingly, the researchers were able to isolate the erased script.

The first deciphered lines — featuring the word “Aquarius” and descriptions of the constellation’s bright stars — were revealed last month, the Franco-British research team said, and the effort is continuing.

The passages read so far suggest that, contrary to claims made by some archaeologists, the works of the Roman astronomer Claudius Ptolemy (AD 100–170) were original rather than simple copies of Hipparchus’s findings.

The picture is expected to become clearer once the decipherment is complete, when astronomers will study the stellar coordinates in an effort to reconstruct Hipparchus’s sky.

Among other things, the findings may allow archaeologists to confirm or challenge the prevailing theory surrounding the Farnese Atlas — a 2nd-century Roman statue housed in Naples that is thought to depict constellations drawn from the ancient astronomer’s catalogue.