SN 1054 is a supernova that was first observed on 1054, and remained visible until 1056. The event was recorded in contemporary Chinese astronomy, and references to it are also found in a later (13th-century) Japanese document, and in a document from the Islamic world. Furthermore, there are a number of proposed, but doubtful, references from European sources recorded in the 15th century, and perhaps a pictograph associated with the Ancestral Puebloan culture found near the Peñasco Blanco site in New Mexico, United States. The remnant of SN 1054, which consists of debris ejected during the explosion, is known as the Crab Nebula. It is located in the sky near the star Zeta Tauri (ζ Tauri). The core of the exploding star formed a pulsar, called the Crab Pulsar (or PSR B0531+21). The nebula and the pulsar that it contains are some of the most studied astronomical objects outside the Solar System. It is one of the few Galactic supernovae where the date of the explosion is well known. The two objects are the most luminous in their respective categories. For these reasons, and because of the important role it has repeatedly played in the modern era, SN 1054 is one of the best known supernovae in the history of astronomy. The Crab Nebula is easily observed by amateur astronomers thanks to its brightness, and was also catalogued early on by professional astronomers, long before its true nature was understood and identified. When the French astronomer Charles Messier watched for the return of Halley's Comet in 1758, he confused the nebula for the comet, as he was unaware of the former's existence. Motivated by this error, he created his catalogue of non-cometary nebulous objects, the Messier Catalogue, to avoid such mistakes in the future. The nebula is catalogued as the first Messier object, or M1. Identification of the supernova The Crab Nebula was identified as the supernova remnant of SN 1054 between 1921 and 1942, at first speculatively (1920s), with some plausibility by 1939, and beyond reasonable doubt by Jan Oort in 1942. In 1921, Carl Otto Lampland was the first to announce that he had seen changes in the structure of the Crab Nebula. This announcement occurred at a time when the nature of the nebulae in the sky was completely unknown. Their nature, size and distance were subject to debate. Observing changes in such objects allows astronomers to