Halley’s comet bears the name of the astronomer who famously first described its movements through space, but he wasn’t the first to discover its periodic orbit past Earth, new research suggests.
Halley’s comet is named for British astronomer Edmond Halley, who pieced the space rock’s orbit together in 1705 through a combination of his own observations and historical records from other observers. But recent research suggests that Halley was not the first to discover his eponymous comet’s roughly 75-year cycle. Instead, the English monk Eilmer (also known as Aethelmaer) of Malmesbury may have connected two observations of the comet more than 600 years earlier.
In addition to his fascination with flight, Eilmer had a keen interest in astrology and astronomy. As a young boy in 989, he watched a comet blaze through the skies over his home in England, William of Malmesbury wrote. Decades later, in 1066, he saw the comet a second time — and he connected the two events, Simon Portegies Zwart, astronomer at Leiden University in the Netherlands, argues in a new book.
Portegies Zwart writes that according to William of Malmesbury’s account, upon seeing the comet in 1066 Eilmer exclaimed, “You’ve come, have you?…It is long since I saw you; but as I see you now, you are much more terrible, for I see you brandishing the downfall of my mother-country.” At the time, England was in the midst of a succession crisis following the death of King Edward the Confessor, who left no clear heir to the throne. If William’s record is accurate, then Eilmer realized the two “gleaming stars” he witnessed were indeed the same. Either way, it is clear William himself realized the connection.
Halley’s comet is the first comet astronomers recognized as periodic, or recurring. It has a highly elliptical orbit around the sun. This stretched-out orbit causes it to pass by Earth every 72 to 80 years, leaving a bright trail of dust in its wake.
The earliest probable record of Halley’s comet comes from a Chinese chronicle in 239 B.C. Since then, it was recorded dozens of times by astronomers around the world, often interpreted as some sort of omen. The Roman-Jewish historian Flavius Josephus, for example, believed his A.D. 66 sighting of the comet portended the fall of Jerusalem. The comet’s passing was stitched onto the Bayeux Tapestry, which recorded William the Conqueror’s invasion of England in 1066, after it was seen flying over Brittany and the British Isles in April that year.
Halley, the astronomer, connected the comet’s 1531, 1607 and 1682 appearances. He went on to predict its return in 1758. Halley died in 1742 before he could see his forecast play out, but he was vindicated posthumously when the comet did indeed return as expected.
Halley’s calculations were impressive, but Portegies Zwart contends that Eilmer should get credit for putting the comet’s appearances together centuries earlier. He and Michael Lewis, of the British Museum, published a chapter arguing this point in the book “Dorestad and Everything After: Ports, Townscapes and Travelers in Europe, 800-1100” (Sidestone Press, 2025).
You can catch Halley’s — or Eilmer’s — comet on its next pass in late July 2061. Mark your calendars now.