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

A sequence on the Bayeux Tapestry shows King Harold alongside a crowd gazing at the sky, beneath the embroidered caption Isti mirant stella ("those people marvel at the star"). Above Harold sits Halley's Comet, with ghostlike invasion boats in the border below—a Norman framing of Harold as a doomed usurper whose betray…