'Terror of kings': Why the 1066 appearance of Halley's Comet terrified the medieval world

In 1066, the appearance of Halley's Comet sent terror through the medieval world, as depicted on the Bayeux Tapestry. King Harold was shown gazing at the sky with a crowd, beneath the caption "isti mirant stella" (those people marvel at the star), with Halley's Comet portrayed above him, alongside ghostlike invasion boats. Medieval writers widely interpreted the comet as a "terror of kings" or "regum terror," a portent of change in human affairs.

The comet was visible for one to two weeks, appearing in the evening sky from April 24, 1066, and remaining visible for about four months after Harold's coronation. Modern calculations suggest the comet came within approximately 15 million kilometers of Earth, as bright as Venus with a tail extending 15 degrees across the sky. This sudden and bright appearance deeply impressed those who witnessed it.

Medieval writers recorded and described the comet, offering insights into medieval astronomy, its links with astrology, and the broader context of global observation and learning. William of Poitiers linked the comet to Harold's ill-fated kingship, while contemporary historian William of Jumièges noted the comet's appearance with a three-forked tail.

The Anglo-Saxon Chronicles D and C recorded the comet but did not connect it with regime change. Subsequent generations of chroniclers elaborated further on the comet as a portent, with the English historian William of Malmesbury stating that comets foretold either a pestilence in the kingdom or a change in the kingship. Medieval astronomers understood the universe as divided into two realms: the superlunary, the realm of planets and fixed stars, and the sublunary, composed of the four elements. Comets were believed to influence human affairs due to their connection between the two realms.