The British astronomer and mathematician Edmond Halley was not, after all, the first to understand the cycle of the comet that now bears his name. This is shown by research conducted by, among others, Professor Simon Portegies Zwart. It was the monk Eilmer of Malmesbury who, as early as the 11th century, linked two observations of the comet.
The events are described by the 12th-century chronicler William of Malmesbury, but until now this has gone unnoticed by scholars. Portegies Zwart and Lewis now argue that Aethelmaer witnessed both appearances of the comet. Their findings have been published in the book 'Dorestad and Everything After. Ports, townscapes & travellers in Europe, 800-1100'.
Halley identifies the comet's periodicity
Halley discovered that the very bright periodic comet later named after him, 1P/Halley, observed in 1531, 1607 and 1682, was in fact the same comet, returning approximately every 76 years.
Worldwide observations in 1066
In 1066, the comet was observed in China for more than two months. Although it was at its brightest on 22 April 1066, Halley's Comet was not seen in Brittany and the British Isles until 24 April that year. The comet is depicted on the Bayeux Tapestry, which illustrates the events of 1066.
Comet appearances as omens in medieval chronicles
The comet appeared during the brief reign of King Harold Godwinson, from 6 January to 14 October 1066. Source research by Portegies Zwart and Lewis shows that a comet was seen five times in the centuries around this date. In oral tradition, these appearances are associated with the deaths of kings, war or famine in the British Isles. A comet not mentioned in the chronicles, said to precede the death of Archbishop Sigeric of Canterbury in 995, may be interpreted as a historical equivalent of fake news, or as an exaggeration of events, probably intended to frighten the British population with God's wrath over the sins of the people.
The monk Eilmer - or Aethelmaer - of Malmesbury must already have been elderly when he saw Halley's Comet for the second time in 1066. He realised that he had seen the same comet earlier, in 989. Once again, as was customary at the time, the king was warned of impending disaster.
Call for reassessment and further research
The researchers argue that Halley's Comet should be given a different name, as it had already been observed twice centuries earlier. Portegies Zwart says: 'This research was great fun to do, but I also found it challenging to work within such an interdisciplinary project alongside a historian. Nevertheless, we plan to carry out further research into this kind of periodic comet.'
This press release originally appeared on astronomie.nl.
