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SN 1054 is a supernova that was first observed on 4 July 1054 AD, and that lasted for a period of around two years. 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 Arab 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. 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 it contains are 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 the best known supernova 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. Due to 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.〔C. O. Lampland, ''Observed Changes in the Structure of the "Crab" Nebula (N. G. C. 1952)'', ''Publications of the Astronomical Society of the Pacific'', 33, 79–84 (1921) 〕 This announcement occurred at a time when the nature of the nebulas in the sky was completely unknown. Their nature, size and distance were subject to debate. Observing changes in such objects allows astronomers to determine whether their spatial extension is "small" or "large", in the sense that notable changes in an object as vast as our Milky Way cannot be seen over a small time period, such as a few years, whereas such changes are possible if the size of the object does not exceed a diameter of a few light-years. Lampland's comments were confirmed some weeks later by John Charles Duncan, an astronomer at the Mount Wilson Observatory. He benefited from photographic material obtained with equipment and emulsions that had not changed since 1909; as a result the comparison with older snapshots was easy and emphasized a general expansion of the cloud. The points were moving away from the centre, and did so faster as they got further from it.〔John C. Duncan, ''Changes Observed in the Crab Nebula in Taurus'', ''Proceedings of the National Academy of Sciences'', 7, 179–181 (1921) 〕 Also in 1921, Knut Lundmark compiled the data for the "guest stars" mentioned in the Chinese chronicles known in the West.〔Knut Lundmark, ''Suspected New Stars Recorded in Old Chronicles and Among Recent Meridian Observations'', ''Publications of the Astronomical Society of the Pacific'', 33, 225–239 (1921) (Voir en ligne ).〕 He based this on older works, having analysed various sources such as the ''Wenxian Tongkao'', studied for the first time from an astronomical perspective by Jean-Baptiste Biot in the middle of the 19th century. Lundmark gives a list of 60 ''suspected novae'', the generic term for a stellar explosion, in fact covering two defined phenomena, novae and supernovae. The nova of 1054, already mentioned by the Biots in 1843,〔Édouard Biot, "Catalogue des étoiles extraordinaires observées en Chine depuis les temps anciens jusqu’à l’an 1203 de notre ère", published in ''Connaissance des temps ou des mouvements célestes, à l’usage des astronomes et des navigateurs, pour l’an 1846''. 1843. 〕 is part of the list. It stipulates the location of this guest star in a note at the bottom of the page as being "close to NGC 1952", one of the names for the Crab Nebula, but it does not seem to create an explicit link between them. In 1928, Edwin Hubble was the first to note that the changing aspect of the Crab Nebula, which was growing bigger in size, suggests that it is the remains of a stellar explosion. He realised that the apparent speed of change in its size signifies that the explosion which it comes from occurred only nine centuries ago, which puts the date of the explosion in the period covered by Lundmark's compilation. He also noted that the only possible nova in the region of the Taurus constellation (where the cloud is located) is that of 1054, whose age is estimated to correspond to an explosion dating from the start of the second millennium. Hubble therefore deduced, correctly, that this cloud was the remains of the explosion which was observed by Chinese astronomers.〔Edwin Hubble, ''Novae or Temporary Stars'', ''Astronomical Society of the Pacific Leaflets'', 14, 55–58 (1928) 〕 Hubble's comment remained relatively unknown as the physical phenomenon of the explosion was not known at the time. Eleven years later, when the fact that supernovae are very bright phenomena was highlighted by Walter Baade and Fritz Zwicky〔Walter Baade & Fritz Zwicky, ''On Super-novae'', ''Proceedings of the National Academy of Sciences'', 20, 254–259 (1934) 〕 and when their nature was suggested by Zwicky〔Fritz Zwicky, ''On Collapsed Neutron Stars'', ''Astrophysical Journal'', 88, 522–525 (1938) 〕 Nicholas Mayall proposed that the star of 1054 was actually a supernova,〔Nicholas U. Mayall, ''The Crab Nebula, a Probable Supernova'', ''Astronomical Society of the Pacific Leaflets'', 3, 145–154 (1939) 〕 based on the speed of expansion of the cloud, measured by spectroscopy, which allows astronomers to determine its physical size and distance, which he estimated at 5000 light-years. This was under the assumption that the velocities of expansion along the line of sight and perpendicularly to it were identical. Based on the reference to the brightness of the star which featured in the first documents discovered in 1934, he deduced that it was a supernova rather than a nova. This deduction was subsequently refined, which pushed Mayall and Jan Oort in 1942 to analyse historic accounts relating to the guest star more closely (see below). These new accounts, globally and mutually concordant, confirm the initial conclusions by Mayall and Oort in 1939 and the identification of the guest star of 1054 is established beyond all reasonable doubt. Most other historical supernovas are not confirmed so conclusively: supernovas of the first millennium (SN 185, SN 386 and SN 393) are established on the basis of a single document each, and so they cannot be confirmed; in relation to the supposed historical supernova which followed the one in 1054, SN 1181, there are legitimate doubts concerning the proposed remnant (3C58) and an object of less than 1000 years of age. Other historical supernovae of which there are written accounts which precede the invention of the telescope (SN 1006, SN 1572 and SN 1604) are however established with certitude. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SN 1054」の詳細全文を読む スポンサード リンク
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