📜 Halley's comet renamed after a medieval monk?

Who truly identified the regular return of Halley's Comet? A common misconception attributes this discovery to astronomer Edmond Halley, but a medieval monk may have preceded him by several centuries.

Indeed, as early as the 11th century, Eilmer of Malmesbury, an English monk, likely established the link between two bright appearances separated by decades. According to research presented in the book Dorestad and Everything After, he observed the comet in 989 and again in 1066, understanding it was the same object. This intuition, recorded in historical chronicles, remained in obscurity until a recent analysis.


The 1066 appearance was widely documented around the world. Chinese astronomers tracked it for over two months, noting its peak brightness in late April. In Europe, it was depicted on the Bayeux Tapestry, where it is associated with contemporary events. These multiple observations show that the comet was already a notable phenomenon long before modern calculations.

Later, in the 17th century, Edmond Halley systematized this knowledge by calculating the comet's orbit. Using data collected over several passages, he established that the object observed in 1531, 1607, and 1682 was identical and would return periodically. His approach marked significant progress for astronomy, even though the idea of periodicity already existed.

In the Middle Ages, comets were often perceived as signs foretelling misfortunes, such as war or the death of rulers. The 1066 comet was thus interpreted as an omen during King Harold's reign. Some accounts even exaggerated its appearances to influence populations.


The researchers behind this discovery now propose reconsidering the comet's name, arguing that its periodicity was known long before Halley.

Recording astronomical observations in the Middle Ages

In the Middle Ages, sky observations were often made by monks or chroniclers, who noted celestial events in manuscripts. These documents, such as the chronicles of William of Malmesbury (not to be confused with Eilmer of Malmesbury), served both as historical records and as supports for the study of natural phenomena. They testify to an attention paid to comets, eclipses, or shooting stars, even without sophisticated tools.

These records were motivated by religious or cultural beliefs, with comets frequently associated with omens. For example, the appearance of Halley's Comet in 1066 was linked to the Norman conquest of England, as shown in the Bayeux Tapestry. This influenced how events were reported and remembered.

Despite these biases, medieval data offer valuable information for modern astronomers. They allow the reconstruction of past comet cycles and the refinement of orbital models. The rediscovery of Eilmer of Malmesbury's note on periodicity shows that scientific ideas could emerge even in contexts where technology was limited.

Today, historians and scientists collaborate to analyze these archives with new methods, such as carbon dating or textual analysis. This interdisciplinary approach helps separate observed facts from cultural interpretations, thereby enriching our knowledge of the history of astronomy.