The ‘guest star’ of 1054: Song astronomers record a supernova

Chinese astronomers called star-like objects that appeared for a time in the sky ‘guest stars’ and reported them to the throne as portents. The History of Song records that on a jichou day in the fifth month of the first year of Zhihe — 4 July 1054 — a guest star appeared south-east of Tianguan, ‘perhaps several inches’ away, and faded after more than a year. The Song huiyao adds that it was seen at dawn in the east and was visible in daylight like Venus for 23 days, with rays in all directions and a reddish-white colour. On 27 August 1054 the official Yang Weide interpreted it as a sign that the state possessed a man of great worth, and the court congratulated Emperor Renzong. On 6 April 1056 the astronomical bureau reported that the star had vanished, after some 642 days of visibility. A later chronicle gives the day as yichou, which is taken to be a copying error.

The star was also noted in Japan — the 13th-century diary of Fujiwara no Teika dates it a month earlier, probably by mistake — and by the Christian physician Ibn Butlan, who linked a ‘spectacular star’ in Gemini with epidemics in Constantinople and Fustat. No certain European record exists, and scholars argue over several vague candidates. A pictograph at Peñasco Blanco in Chaco Canyon, showing a crescent moon beside a star, may record the morning of 5 July 1054, when the Moon passed close to the supernova, but this cannot be confirmed.

In 1921 Knut Lundmark listed the guest star of 1054 near the Crab Nebula, in 1928 Edwin Hubble suggested that the expanding nebula was its remnant, and in 1942 Nicholas Mayall and Jan Oort established the identification beyond reasonable doubt. The Crab Nebula, Messier's object M1, contains a pulsar formed from the core of the exploded star, and both are among the most studied objects outside the Solar System. The puzzling statement that the star lay south-east of Tianguan, whereas the nebula lies to the north-west, was explained by David Green and Richard Stephenson in 2003: in Song usage a guest star said to ‘guard’ a star lay below it.