The Crab Nebula is the remnant of a supernova seen in 1054

The Crab Nebula is the wreck of a star whose explosion was recorded on July 4, 1054, when Song-dynasty Chinese astronomers logged a “guest star” in Taurus that stayed visible in daylight for 23 days and at night for about 653 days. Japanese astronomers saw it too, and so did Ibn Butlan, a Christian physician from Baghdad travelling in the Middle East.

Then it was forgotten. Linking the 1054 star to the glowing cloud in Taurus took almost nine centuries and some 20th-century detective work:

• 1731: English astronomer John Bevis spots the nebula through a telescope. Charles Messier later mistakes it for Halley’s Comet, and it becomes M1, first entry in his catalogue of comet look-alikes.
• 1844: its leg-like filaments earn it the name “Crab”.
• Early 1900s: comparing photographs, John Duncan finds the cloud is expanding, so it must have started from a point at a knowable time.
• 1928: Edwin Hubble works the expansion backwards and suggests the nebula was born about 900 years earlier, matching the Asian guest star.
• 1939: Nicholas Mayall argues the 1054 event was a supernova, not an ordinary nova.

The match still has loose ends. European records are oddly thin, but one Roman subdeacon described a brilliant orb at the hour of Pope Leo IX’s death on April 19, 1054, which some researchers read as a sign the star exploded months before the Chinese sighting. And if the nebula had always grown at today’s rate, the explosion would date later than 1054; but the complex processes driving the expansion make its rate hard to measure.

The nebula’s centre holds the collapsed core of the dead star: a neutron star spinning so fast that its beams sweep past Earth about 30 times a second. Around it, the debris now spans some six light-years, about 6,500 light-years away.