According to a new study published in arXiv, an 11th-century English monk first documented multiple appearances of Halley’s Comet, more than 600 years before Edmond Halley codified its orbit.
Simon Portegies Zwart, an astronomer at Leiden University, and Michael Lewis, one of the British Museum’s scientists, conducted the study. By comparing medieval chronicles and astronomical records, the researchers conclude that the 11th-century monk Eilmer of Malmesbury, known as Aethelmaer, discovered the comet’s periodic return after observing it twice within his lifetime.
In his medieval writings, Eilmer reportedly observed the comet in 989 and 1066, both times regarding the comet as the same celestial object.
Halley’s Comet was evident in China for over two months and was most brightly observed on April 22. It was spotted in Brittany and the British Isles two days later and appears on the Bayeux Tapestry, the oldest known visual representation of the comet. The tapestry traces the heavenly event back to the Norman Conquest and the tumultuous era of Harold Godwinson.
In fact, as Zwart and Lewis note, comets were historically construed as portents of disaster, often tied to the deaths of kings, war, or famine. They find five comet sightings over the period surrounding 1066.
By 1066, Eilmer was already an elderly man, yet he appears to have remembered witnessing the same comet decades earlier and to have understood its reappearance as part of a repeating cycle. The researchers argue that this challenges the traditional narrative, which credits Edmond Halley as the first to recognise the comet’s roughly 76-year orbit.
Although Halley’s mathematical proof remains a landmark, the authors suggest that the comet’s name may need to be reevaluated. Portegies Zwart said the project was challenging and rewarding, and that the group intended to continue investigating historical evidence of periodic comets through partnerships between astronomy and history.
Sources : arXiv – https://doi.org/10.48550/arXiv.2511.14809
