Medieval Monk Eilmer May Have Identified Halley's Comet's Orbit Centuries Before Edmond Halley

New research suggests that the English monk Eilmer of Malmesbury may have identified the periodic orbit of Halley's Comet centuries before British astronomer Edmond Halley.

Edmond Halley is widely recognized for piecing together the comet's orbit in 1705, using a combination of his own observations and historical records. However, astronomer Simon Portegies Zwart of Leiden University and Michael Lewis of the British Museum propose in a new book that Eilmer connected two observations of the comet more than 600 years earlier.

Eilmer: Monk, Aviator, and Observer

Eilmer, also known as Aethelmaer, was an English monk with a reported interest in aviation, having supposedly attempted flight in the late 990s or early 1000s. According to 12th-century historian William of Malmesbury, Eilmer glided approximately 660 feet (200 meters) before a landing incident.

In addition to his interest in flight, Eilmer was keen on astrology and astronomy. William of Malmesbury recorded Eilmer observing a comet in 989. Decades later, in 1066, he saw the comet a second time.

A Recurring Comet?

Portegies Zwart argues that Eilmer connected these two events, realizing they were sightings of the same recurring comet.

William of Malmesbury's account suggests Eilmer recognized the comet's return, reportedly exclaiming about its reappearance and its perceived ominous nature during England's succession crisis.

Halley's Comet Through History

Halley's Comet is recognized as the first comet astronomers identified as periodic, completing an elliptical orbit around the sun every 72 to 80 years. Its earliest probable record is from a Chinese chronicle in 239 B.C.

Historical sightings, suchs as the one in A.D. 66 noted by Flavius Josephus and its depiction in the Bayeux Tapestry after its 1066 appearance, often led to interpretations of the comet as an omen.

Edmond Halley's Legacy and New Claims

Edmond Halley connected the comet's appearances in 1531, 1607, and 1682, accurately predicting its return in 1758. Halley died in 1742, prior to the comet's predicted return, which subsequently occurred as he forecast.

Portegies Zwart and Lewis's research published in "Dorestad and Everything After: Ports, Townscapes and Travelers in Europe, 800-1100" contends that Eilmer should receive credit for linking the comet's appearances centuries earlier.