The history of astronomy’s most famous comet may need to be revised. New research suggests that six centuries before astronomer Edmond Halley scientifically described in 1705 the periodic appearance of the comet that now bears his name, another person had already understood that it was the same celestial object observed at different times.
It cannot be said, strictly speaking, that Halley was the discoverer of this comet. The British scientist himself acknowledged that he had relied on previous historical records for his conclusions. In any case, he was the first to demonstrate, using the scientific method, that the appearances of 1531, 1607, and 1682 were of a single celestial body that returned periodically, approximately every 76 years.
That deduction marked a milestone in the history of science and contributed decisively to dispelling the view that comets were supernatural omens.
English monk who saw comet 600 years before Halley
However, a recent study suggests that this insight about the recurrence of the phenomenon was already present, in embryonic form, in medieval Europe — specifically, thanks to an English monk who lived in the late 10th and early 11th centuries.
The study, carried out by astrophysicist Simon Portegies Zwart and historian Martin Lewis, identifies Eilmer of Malmesbury — also known as Æthelmær or Oliver of Malmesbury — as a possible previous observer. He was a Benedictine monk who is believed to have seen the comet on two separate occasions, almost eight decades apart, in the years 989 and 1066.
The results are published in the volume “Dorestad and Everything After: Ports, Townscapes & Travellers in Europe, 800-1100,” a work dedicated to knowledge and travel in medieval Europe.
According to the authors, Eilmer may have recognized in 1066 the same celestial body he had seen in his youth, an exceptional deduction for his time, based on personal memory and his noting the comet’s reappearance over a period of time that was unusual in the Middle Ages.
Comet appeared in the sky in 1066
The appearance of the comet in 1066 is widely documented. It was observed for more than two months in China, where imperial astronomers accurately recorded its trajectory and brightness.
It reached its maximum brilliance on April 22 and, shortly afterward, became visible in the skies of northwestern Europe. Its image was immortalized in the Bayeux Tapestry, the oldest known representation of the phenomenon, woven into that visual narrative of the Norman conquest of England.
The event coincided with the turbulent reign of Harold II, which ended with the defeat of the English at the Battle of Hastings in October of that same year. In the medieval mindset, celestial phenomena were almost always interpreted as omens of impending calamities — wars, epidemics, or the downfall of rulers — and the comet was no exception.
By analyzing Latin and Anglo-Saxon chronicles, researchers have identified up to five supposed appearances of the comet between the late 10th and 11th centuries. In some cases, they point out, it is difficult to separate actual astronomical observation from later symbolic interpretation. A supposed sighting in the year 995, retrospectively linked to the death of Archbishop Sigeric of Canterbury, may be more of a narrative construct with a moral purpose than a verifiable astronomical event.
According to the chronicler William of Malmesbury, one of the most reliable sources from medieval England, Eilmer was already an old man when he saw the comet again in 1066 and identified it as the same one he had observed as a child.
True to the worldview of his time, he interpreted the phenomenon as a dire omen for the kingdom, combining natural observation with warnings of a moral and political nature.
In light of this information, the authors of the study suggest reconsidering, at least from a historical point of view, the exclusive attribution of the discovery to Halley.
Without diminishing the achievements of the 18th-century astronomer, Portegies Zwart emphasized that Eilmer’s observation constitutes an early example of astronomical reasoning based on direct experience. “This interdisciplinary approach, combining astronomy, history, and philology, can help us discover that other periodic phenomena were already recognized before the modern era,” the researcher notes.
Halley’s Comet will be visible again
The year 2061 is when Halley’s Comet is next expected to be visible from Earth. In its elliptical orbit, it approaches the sun to within 0.59 astronomical units and moves away to about 36 astronomical units, beyond the orbit of the planet Neptune, completing its journey in approximately 76 years.
When it returns, it will evoke not only the name of Edmond Halley but also that of a medieval monk who, centuries earlier, recognized that this celestial visitor had already passed by before.
This story was first published by ACI Prensa, the Spanish-language sister service of EWTN News. It has been translated and adapted by EWTN News English.