Officials of the Song dynasty documented a "guest star" bright enough to be visible in daylight for weeks, recording its position and duration with remarkable precision. Centuries later, astronomers identified the remnant of this explosion as the Crab Nebula, one of the most studied objects in the sky and a cornerstone of modern astrophysics.
Song dynasty astronomers, whose job was partly to interpret celestial omens for the emperor, watched a point of light appear in the sky bright enough to be visible during the day for some 23 days and remain visible to the naked eye at night for nearly two years. They recorded it methodically in official histories as a "guest star" near the star now catalogued as Zeta Tauri, noting its color and gradual fading with an attention to detail that would prove invaluable a millennium later.
Similar sightings appear to have been recorded by Japanese and Arab observers, and possibly by Ancestral Puebloan peoples in the American Southwest, whose rock art in Chaco Canyon may depict the same event, a crescent moon beside a bright star, matching the supernova's calculated position.
It was not until the 1920s that astronomers connected this ancient record to the Crab Nebula, an expanding cloud of gas and dust roughly 6,500 light-years away, confirming it as the debris of a star's violent death. At its heart spins the Crab Pulsar, a neutron star rotating some 30 times per second, a lighthouse-like remnant that has become one of astronomy's most valuable natural laboratories for studying extreme physics.