star in China and Japan, although clearly based on different sources. Fujiwara no Teika's interest in the guest star seems to have come accidentally whilst observing a comet in December 1230, which prompted him to search for evidence of past guest stars, among those SN 1054 (as well as SN 1006 and SN 1181, the two other historic supernovas from the early second millennium). The entry relating to SN 1054 can be translated as: The source used by Fujiwara no Teika is the records of Yasutoshi Abe (Onmyōdō doctor), but it seems to have been based, for all the astronomical events he has recorded, on documents of Japanese origin. The date he gives is prior to the third part of ten days of the lunar month mentioned, which corresponds to the period of between 30 May and 8 June 1054 of the Julian calendar, which is around one month earlier than Chinese documentation. This difference is usually attributed to an error in the lunar months (fourth place and fifth place). The location of the guest star, clearly straddling the moon mansions Shen and Zuixi, corresponds to what would be expected of a star appearing in the immediate vicinity of Tianguan. Ibn Butlan (Iraq) While SN 1006, which was significantly brighter than SN 1054, was mentioned by several Arab chroniclers, there exist no Arabic reports relating to the rather faint SN 1181. Only one Arabic account has been found concerning SN 1054, whose brightness is between those of the last two stars mentioned. This account, discovered in 1978, is that of a Nestorian Christian doctor, Ibn Butlan, transcribed in the Uyun al-Anba, a book on detailed biographies of physicians in the Islamic world compiled by Ibn Abi Usaybi'a (1194–1270) in the mid-thirteenth century. This is a translation of the passage in question: The three years cited (AH 445, 446, 447) refer, respectively, to: 23 April 1053 – 11 April 1054, 12 April 1054 – 1 April 1055, and 2 April 1055 – 20 March 1056. There is an apparent inconsistency in the year of occurrence of the star, first announced as 446, then 445. This problem is solved by reading other entries in the book, which quite explicitly specify that the Nile was low at 446. This year of the Muslim calendar ran from 12 April 1054 to 1 April 1055, which is compatible with the appearance of the star in