SN 1054, is a supernova that was first observed as a new "star" in the sky on July 4, 1054 AD, hence its name, and that lasted for a period of around two years. The event was recorded in multiple Chinese documents and in one document from the Arab world. While it has been hypothesized that SN 1054 was also observed by American-Indian tribes and Europeans, it has not been conclusively proven. 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). Some of the remnant of the explosion 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. It was because of this error that 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. Collection of historical records SN 1054 is one of eight Galactic supernovae about which written testimony describing the explosion has survived, and can therefore be identified as such. In the nineteenth century, modern astronomers began to take an interest in the historic records; which they then identified, compiled, and studied as part of their research on recent novae, comets, and later, the supernovae. The first people to attempt a systematic compilation of records from the Far East were the members of the Biot family: the sinologist Édouard Biot translated for his father, the astronomer Jean-Baptiste Biot, passages from the astronomical treatise of the 348 volume Chinese encyclopaedia, the Wenxian Tongkao, in 1843. Almost 80 years later, in 1921, Knut Lundmark undertook a similar effort based on a greater number of sources. In 1942, Jan Oort, convinced that the Crab Nebula was the "guest star" of 1054 described by the Chinese, asked sinologist Jan Julius Lodewijk Duyvendak, to help him compile new evidence on the observation of the event. Stars which appeared temporarily in the sky were generically called “guest stars” by Chinese astronomers. The guest star of 1054 occurred during the reign of the Emperor Renzong of the Song dynasty (960-1279). The relevant year is recorded in Chinese documents as "the first year of the Zhihe era". "Zhihe" was an era name used during the reign of Emperor Renzong, and corresponds to the years 1054-1056 C.E., so the first year of the Zhihe era corresponds to the year 1054 C.E. Six accounts from China relate the observation of the phenomenon. Like almost all of the records relating to the guest star, none of them are first hand: the oldest was about a century after the apparition of the star. Some of these accounts are nevertheless remarkably well preserved, and are used to reconstruct the essential information concerning the observation of the explosion. The Wenxian Tongkao is the first known source of Far-Eastern testimony known of by Western astronomers. It is this that was translated by Édouard Biot in 1843. This source, compiled by Ma Duanlin in 1280, is relatively brief. The text states: Zhihe era of the reign, first year, fifth lunar month, ji-chou day. A guest star has appeared to the south-east of Tianguan, perhaps several inches away. After a year or more, it gradually disappeared. "Tianguan" is the traditional Chinese name for Zeta Tauri. The Xu Zizhi Tongjian Changbian ("Long compilation of the continuation of the Zizhi Tongjian"), a book covering the period of 960-1126 and written 40 years or so later by Li Tao (1114–1183), contains the oldest Chinese testimonies relating to the observation of the star. It was rediscovered in 1970 by the specialist in Chinese civilisations Ho Peng Yoke and collaborators.[citation needed] It is relatively imprecise in the case of the explosion of SN 1054. A loose translation of what was stated : "First year of the Zhihe era, fifth lunar month, ji-chou day. A guest star has appeared to the south-east of Tianguan, perhaps several inches away [of this star]. (The star disappeared in the third lunar month of the first year of the Jiayou era.)" Song Huiyao The Song Huiyao (literally "Collected important documents of the Song dynasty") covers the period 960-1220. Huiyao is a traditional form of history books in China which aimed mainly to preserve primary sources, and as such are important sources supplementing the official Twenty-Four Histories. The Song dynasty had a specific government department dedicated to compiling the Huiyao, and some 2,200 volumes were published in ten batches during the Song dynasty. However, most of these documents were lost by the time of the Qing Dynasty except for the synopsis and a relatively small portion preserved as part of the imperial Yongle Encyclopedia. In 1809, the portion preserved in the Yongle Encyclopedia was extracted and re-published as the Song Huiyao Jigao (the "draft extract of the Song Huiyao"). Subsequent scholars have worked on the project further and the current edition dates from 1936. This document recounts the observation of the guest star, by focusing on the astronomical aspect, but gives more important information relating to the visibility of the star, by day and by night. Zhihe era, first year, seventh lunar month, 22nd day. [...] Yang Weide declared: "I humbly observe that a guest star has appeared; above the star there is a feeble yellow glimmer. If one examines the divination regarding the Emperor, the interpretation [of the presence of this guest star] is the following: The fact that the star has not overrun Bi and that its brightness must represent a person of great value. I demand that the Office of Historiography is informed of this." All officials congratulated the Emperor, who ordered his congratulations be [back] forwarded to the Office of Historiography. First year of the era of Jiayou, third lunar month, the director of the Astronomical Office said "The guest star has disappeared, which means the departure of the host [that it represents]." Previously, during the first year of the Zhihe era, during the fifth lunar month, it had appeared at dawn, in the direction of the east, under the watch of Tianguan. It had been seen in daylight, like Venus. It had rays stemming in all directions, and its colour was reddish white. Altogether visible for 23 days” Song Shi The Song Shi is the official annals of the Song dynasty. Chapter 12 mentions the guest star, not its appearance but rather the moment of its disappearance. The corresponding entry dated 6 April 1056 indicates : Jiayou era, first year, third lunar month, xinwei day, the director of the Office of Astronomy reported during the fifth lunar month of the first year of the Zhihe era, a guest star had appeared at dawn, in the direction of the east, under the watch of Tianguan. Now it has disappeared. In chapter 56 ("Astronomical treaty") of the same document, the guest star is again mentioned in a chapter dedicated to this type of phenomenon, this time focusing on its appearance, and this is in terms very close to Wenxian Tongkao : Zhihe era of the reign, first year, fifth lunar month, jichou day. A guest star has appeared to the south-east of Tianguan, perhaps several inches away. After a year or more, it gradually disappeared. Qidan Guozhi There is an account of the star from the Khitan Liao Dynasty, which ruled in the area around Manchuria from 907-1125. The book in question, the Qidan Guozhi, was compiled by Ye Longli in 1247. It includes various astronomical notes, some of which are clearly copied from the Song Shi. This entry referring to the star of 1054 seems unique: Chongxi era of the reign of [King Xingzong], twenty-third year eighth lunar moon, the ruler of the realm is dead. It happened before a solar eclipse at noon, and a guest star appeared by Mao. The highest office at the Office of History, Liu Yishou had said "These are omens of the death of the King." This prediction has been realised. Interpretation of Chinese reports The sky on the morning of 4 July, probable date of the first Chinese observation of the supernova (blue square). The supernova emerged from its conjunction with the Sun, and rose about two hours before it, being observed during part of this period and day. Three of these accounts clearly emanate from the same source: those of Wenxian Tongkao, of Xu Zizhi Tongjian Changbian, and of chapter 56 of Songshi, who had evaluated the angular distance from the star to Tianguan according to the formula "perhaps several inches away". The three documents however are in apparent disagreement about the date of appearance of the star. Two mention the day jichou, and the third, the Xu Zizhi Tongjian Changbian, the day yichou. These terms refer to the Chinese sexagenary cycle, corresponding to numbers 26 and 2 of the cycle, which corresponds, in the context where they are cited, respectively, to July 4th and June 10th. The latter date is considered incorrect for several reasons. On the one hand, the terms yichou and jichou are different from one and other by only one character, the first, and these characters are very similar, yichou and jichou written respectively 乙丑 et 己丑, so a typographical error in re-transcription seems possible. For others, the entries of Xu Zizhi Tongjian Changbian follow a strict chronological order, and previous entries also refer to the Chinese sexagenary cycle, concerning the days yiyou (22) and bingxu (24), while later entries relate to the days yiwei (32, part of the sixth lunar moon), bingshen (33), then renyin (39). In this context, it seems far more likely that the use of yichou is a result of an error in re-transcription rather than a chronological misplacing of the entry. The duration of visibility is explicitly mentioned in chapter 12 of Songshi, and slightly less accurately, in the Song Huiyao, the last sighting was the 6th of April 105613, after a very long period of visibility of 642 days. This duration is supported by the Wenxian Tongkao and chapter 56 of the Songshi. According to the Song Huiyao the visibility of the guest star was for only 23 days, but this is after mentioning visibility during daylight. This period of 23 days applies in all likelihood solely to visibility during the day. The account of Qidan Guozhi alluded to the notable astronomical events that preceded the death of King Xingzong. Various historical documents allow us to establish the date of death of the Emperor Xingzong as the 28th of August 1055, during the eighth lunar month of the twenty-fourth (and not twenty-third) year of his reign. The dates of the two astronomical events mentioned (the eclipse and the appearance of the guest star) are not specified, but were probably before the obituary (2 or 3 years at most). Two solar eclipses were visible shortly before that date in the Khitan kingdom, on the 13th of November 1053 and the 10th of May 1054. Of these, only one occurred around noon, that of the 13th of November, it seems likely that this is what the document mentions. As for the guest star, only a rough estimate of location is given, corresponding to the moon mansion Mao. This mansion is situated just east of where the star appeared, as mentioned in the other testimonies (see the section General localisation of the Event below). Since no other known significant astronomical event occurred in this region of the sky during the two years that preceded the death of Xingzong, it seems likely that the text is actually referring to the star of 1054. The location of the guest star can in principle be deducted from the statement “to the south-east of Tianguan, perhaps several inches away “, which for a long time perplexed modern astronomers, because if Tianguan is almost universally regarded as a correspondent for the star Zeta Tauri (ζ Tauri), the Crab nebula, following a clearly old explosion of stars about 1000 years ago, and therefore a natural candidate for this guest star, is not situated in the south-east but to the north-west of this star (see the General localisation of the Event section below). Three texts from Japan mention the guest star. The most detailed of these is that of Meigetsuki. One of the other two, which is less precise, can be taken as his, or at least share a common origin with him. The last record, which is extremely brief, gives very little information. Fujiwara no Teika (1162–1241), a poet and courtier, mentions the guest star of 1054 in his famous diary, the Meigetsuki. Better known for his literary works than for his interest in astronomy, he supplied the most detailed description of the supernova of 1054. His 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: “Tengi era of the emperor Go-Reizei, second year, fourth lunar month, after the middle period of ten days. At chou(a Chinese term for 1-3am), a guest star appeared in the degrees of the moon mansions of Zuixi and Shen. It has been viewed in the direction of the East and has emerged from the Tianguan star. It was as big as Jupiter” The source used by Fujiwara no Teika is unknown, 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 the 8th of 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. Another account exists, taken from Ichidai Yoki, an anonymous document probably compiled during the course of the 14th century. He described the star in a way very similar to the Meigetsuki, omitting several details (hour of apparition, and possibly erroneous parts of the lunar month). The comparison with Jupiter is not present; neither is the possibly incorrect month. In addition, the short text contains many typographical errors, especially involving the second character of Tianguan. Everything suggests that this testimony is from the same source as the Meigetsuki, which could also have been copied. Finally, an even shorter text is included in the astronomical treaty of Dainihonshi (litt. “History of Great Japan”). This text can be translated as : « Era of Tengi of the Emperor Go-Reizei, second year, fourth lunar month. A guest star was seen. » The brevity contrasts with the more detailed descriptions of “guest stars” (actually supernovas) of 1006 and 1181. The reason for the little detail on the entry of 1054 is not known. Like the other two Japanese mentions of the star, it mentions the fourth month and not the fifth. Japan's three documents are in agreement as to the month of observation, corresponding to the fourth lunar moon, one month earlier than the Chinese texts. Whatever the exact date during this month, there seems to be a contradiction between this period and the observation of the guest star: the star was in close proximity to te sun, making day time and night time obervation impossible. This inconsistency of the dates is futher confirmed by a detail in the Meigetsuki : the mention of the double hour chou which corresponds to 1am-3am. This is a long time from sunrise and, since the star and the sun are in close proximity, the star could not possibly rise before the sun.. The Japanese and Chinese testimonies can be reconciled if one considers that there is an error in the month stated in the Japanese observation records. The fact that all the Japanese sources make the same mistake can be interpreted as the fact that they are all from the same source. Doubts as to the month of the observation could have been relieved if the day determined by the Chinese sexagenary cycle had been included, in addition to the observation month, but this is not the casein the Japanese documents. In contrast, the day of the cycle given in the Chinese documents is compatible with the months that they state; reinforcing the idea that the month on the Japanese document is incorrect. For others, the study of other medieval supernovas (SN 1006 and SN 1181) reveals a close proximity in the dates of discovery of a guest star in China and Japan, although clearly based on different sources. Considering the mention of the fourth lunar month it would then be accurate to imagine that in that event, the Japanese have significantly outperformed their Chinese counterparts, a mystery for which an explanation is not forthcoming. The Japanese documents do not specify the visibility in daylight, but compare it to Jupiter, which is visible in daylight, and reports of which appear in the astronomical records of the contemporary Chinese world. The visibility in daylight as described by the Chinese texts is thus validated by the Japanese Documents, and is consistent with a period of moderate visibility, which implies that the star's period of diurnal visibility was very short, even during favourable conditions for observation (a star visible during of sunrise is relatively easy to spot if its position is known and as the background sky becomes more and more luminous). No reports of Korean observations of SN 1054 have survived. This has probably because all astronomical records from the year 1054 are missing from the Koryo-sa, the official chronicle relating to this period. It is the same for 1055. In constast, the years 1052 and 1053 contain a large number of entries related to astronomy. The Koryo-sa was compiled in 1451 and it appears likely that, by that time, any document relating to astronomical events observed in 1054 had been lost. No other Korean documents relating to the “guest star” of 1054 have been found since. Traditionally, the astronomers of the Arab world were more interested in cyclic and predictable phenomena than those of an unexpected nature such as a “guest star”, perhaps under the influence of Aristotle, who said that the immutability of the heavens, comets and other novæ should be considered as weather events rather than astronomy. This would explain the low number of “guest stars”, a term that has no equivalent in medieval Europe or in the Arab world. If SN 1006, which was significantly brighter, was mentioned by several Arab chroniclers, there exist no Arab reports relating to the rather faint SN 1181. Only one Arab account has been found concerning SN 1054, whose brightness is between those of the last two stars mentionned. This account, discovered in 1978, is that of a Nestorian Christian doctor, Ibn Butlan, transcribed in the Uyun al-Anba, a book compiled by Ibn Abi Usaybi'a (1194–1270) in the mid-thirteenth century. This is the passage in question : "I copied the following hand written testimony [that of Ibn Butlan]. He stated: “One of the famous epidemics of our time has occurred when a spectacular star appeared in [the zodiac star] Gemini, of the year 446 [of the Muslim calendar]. In the autumn of that year, fourteen thousand people were buried in Constantinople. Thereafter, in the middle of the summer of 447, the majority of the Fostat people [Le Caire] and all foreigners died”. He [Ibn Butlan] continues: “While this spectacular star appeared during the sign of Gemini [...] it provoked the beginning of the Fostat epidemic when the Nile was low in 445.” " The three years cited (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 the 12th of April 1054 to the 1st of April 1055, which is compatible with the appearance of the star in July 1054, as its location (admittedly rather vague), is in the astrological sign of Gemini (which, due to Axial precession, covers the eastern part of the Constellation Taurus).The date of the event in 446 is harder to determine, but the reference to the level of the Nile refers to the period preceding its annual flood, which happens during the summer. Since the 1980s, several old European documents have been identified as possible observations of the supernova.[2][3][4][5][6] The relevance of these documents has been criticised, as the dating that they indicate does not correspond to that of the Chinese documents, which they precede by 2 or 3 months, with no mention of any subsequent sightings of the supernova. They are also very imprecise and unconvincing from an astronomical perspective, even when collated. They would also be impossible to interpret in the sense of an observation of a supernova if no information had been preserved from the Chinese accounts. These attempts at linking a genuine celesatial event to very imprecise documents have been strongly criticised by a number of authors,[7] who view them a seeking to promote the existence of sightings of the event in Europe and as being "anxious to ensure that this event was recorded by Europeans". The lack of accounts from European chroniclers has long raised questions. In fact, it is known that supernova of 1006 was recorded in a large number of European documents, albeit not in astronomical terms. Among the proposed explanations for the lack European accounts of SN 1054 is its concurrence with the East-West Schism[8] is prominent. In fact, the date of the excommunication of the Patriarch of Constantinople Michael I Cerularius (16 July) corresponds to the star reaching its maximum brightness and being visible in the daytime. This is only an unverifiable hypothesis, and it is difficult to explain how an account of an event which was visible a priori to everyone could have disappeared without a trace. The fact is however, that European documents of the 11th century were written by people who, despite their extensive learning, possessed extremely limited knowledge of astronomy, and could not even consistently recognise the stars which form various astronomical conjunctions (see examples below). The first suggestion of a European account of a sighting of the supernova was made in 1980 by the Italian astronomer Umberto Dall'Olmo (1925–1980).[2] The following passage which reports an astronomical sighting is taken from an account compiled by Jacobus Malvecius in the 15th century: " And in those days, an immensely bright star appeared in the circle of the moon, around the first day of its separation from the sun."[citation needed] The date that this passage was written is not specified, but in it, there is a reference to an earthquake in Brescia, which has been identified as taking place on 11 April 1064. Dall'Olmo did not propose any explanation of this apparent mismatch of ten years between the supernova and the earthquake, besides the hypothesis that it could be the result of a transcription error.[citation needed] Even if this were not the case, the absence of a precise date and position makes the phenomenon difficult to identify, and it couldsimply be a conjunction between the moon and a planet (probably Venus or Jupiter), or a concealment of a planet by the moon. The account of a supernova sighting which is considered the most feasible comes from a medieval chronicle from the region of Bologna, the Cronaca Rampona. This text, a subject of astronomers' attention since 1972,[9] was interpreted as a possible sighting of the supernova in 1981,[3] and again in 1999.[6] The part of the chronicle that was highlighted indicates that: “ In the year of Christ Ml8, Pope Stephen IX has come to the throne [...] Also in this year of Christ Ml8, Henry III reigned [or “ lived ”] for xl9 years. He went to Rome for the first time in the month of May. At this time, famine and death was upon the whole world. He stayed in the province of Tibur for three days in the month of June [...] At that moment, a very brightly-shining star entered into the circle [or the circuit] or the new moon, in the thirteenth Calends at the beginning of the night [NB 1] Without even discussing the last, astronomical part of the text, skeptics point out at least two discrepancies in the following : Pope Stephen IX became Pope in 1057, not 1058, and Emperor Henry III who is mentioned, actually Henry III, Holy Roman Emperor, was born in 1017, 39 and not 49 years before 1058, his reign having started in 1039 (King of the Romans, then as emperor of the Romans from 1046 after being consecrated by Pope Clement II during the course of his brief pontificate). Henry III, therefore, was dead in 1056, and his reign could not have coincided with that of Stephen IX. It seems more likely that the text was the subject of various alterations, as the date format (for example “ Ml8 ” for 1058, the second character of “ Ml8 ” being the lower case letter L), with a mix of Roman (upper and lower case) and Arab characters, was common in the period when the Cronaca Rampona was written (15th century) but not that of the supernova four centuries earlier.[3] Furthermore, associating the event described with the sighting of a supernova in 1054 would require the supposition that the Cronaca Rampona entry was in the wrong place in relation to the rest of the document, as the different entries are in chronological order and several previous entries are later than 1054 ( in order, the previous entries refer to 1046, 1049, 1051, 1055, 1056, written in a mix of Arab and Roman characters, namely Mxl6, Mxl9, Mli, Mlv and Ml6). Additionally, there is a discrepancy with the date of the new moon. The term Calends, which refers to the Roman calendar, can be written in the ordinary form of the Gregorian calendar, and the phase of the moon can be calculated from it. It is clear that the new moon did not occur on the thirteenth day of the Calends in any month in 1054.[NB 2] All of this is in strong opposition to the precision of the dates of references to eclipses in medieval European chronicles : a study of 48 partial or total solar eclipses from 733 to 1544, reveals that 42 dates out of 48 are correct, and of the six remaining, three are incorrect by one of two days and the three others give the correct day and month, but not the year.[10] Finally, even considering that the stated event corresponds to May or June 1054 nevertheless, and describes a conjunction between the already visible supernova and the moon, another problem arises : during those months, the moon did not pass very close to the location of the supernova. Incidentally, the vocabulary used in the Latin text is somewhat unusual. The Latin word translated into English as circle is circuitu, used in place of the more commonly used circulus, but this semantic variant does not seem to change the sense of the text, which, in all possible translations of circuitu, suggests an object which is found on or close to the moon's path of travel. Therefore, it is possible that the account describes an approach or a concealment of a planet by the moon, contemporary to the suggested date (1058). This scenario is corroborated by two contemporary documents which are perfectly dated and describe a conjunction and a planetary concealment by the moon in relatively similar terms. These two documents, unearthed by Robert Russell Newton,[9] are taken from the Annales Cavenses, Latin chronicles from la Trinità della Cava (Province of Salerno, Southern Italy). They mention a “bright star that entered into the circle of the new moon”[NB 3] on dates corresponding to 17 February 1086 and 6 August 1096. Calculations indicate that Venus was eclipsed by the moon for half an hour on the 17th February. On the 6th August, Jupiter passed to less than one degree from the moon after a lunar eclipse which was also mentioned in the chronicle.[7] The fact that the chronicler or chroniclers did not realise that they had seen a planet rather than a new star demonstrates the weak astronomical knowledge of the scholars of the time, whose astronomical accounts are actually very difficult to interpret and attribute to a rare event. In 1992, a group of Italians proposed a Flemish text as an account of a sighting of the supernova.[4] The text, from Saint Paul's church—no longer existent—in the Flemish town of Oudenberg, describes the death of Pope Leo IX in Spring 1054. “On the eighteenth calends of May, on the second day of the week at around midday, the soul [of Pope Leo IX] departed. At the moment it left his body, in Rome, where he rests, but also everywhere on earth, a circle of extraordinary brightness appeared in the sky for half an hour.”[NB 4] The date described corresponds to the 14th April 1054, the “ second day of the week ” being a Monday, according to the custom of the time. This simple date causes several problems : numerous historical documents describing the death of the Pope state the date as the 19th April and not the 14th. Additionally, neither of these days were Mondays. The astronomical part of the text is also difficult to interpret and associate with the supernova. The description of the phenomenon, which is difficult to identify, is very brief, which contrasts with the timescale of a supernova. Il is not given a location in the sky and the time of the sighting is not given, not even whether it was during the day or the night. There are a priori numerous optical or atmospheric phenomena which can impress a chronicler who is not a specialist in astronomy, such as auroras (at night) or a solar halo (in the daytime). Most importantly, the reference to “ everywhere on earth ” could correspond to a non-localised event, but it is not possible to know the exact meaning of such a reference. In a work entitled De Obitus Leonis, the author, Libuinus, reported an unusual celestial phenomenon which was seen on the day that Leo IX died by a group of pilgrims lead by a certain Albertus, who were in the region of Todi (Umbria north of Rome). He seems to have confirmed seeing : “like a path by which his soul had been escorted by the angels to the Heavens, clothed in brightness and countless lamps.”[NB 5] The nature of the observed phenomenon is difficult to identify, as the subject is enshrouded in mystery. Certain authors[4][6] have proposed that he actually described the supernova. A favourable moment would have been at dusk, when the sun was setting before the star ζ Tauri. However, on that night, a concentration of planets was in that area of the sky : Mars, Mercury, Venus, and Jupiter slightly further away. That area of the sky is also rich in bright stars (the constellation of Orion, Sirius, Capella etc.), and it is possible that these, along with the planets, formed the “ countless lamps ” in Albertus' account. Considering this vast concentration of brightness, the supernova's presence would not have been remarkable. Just like the preceding account, this text directly links the death of the Pope to an “ extraordinary ” event, which could have been done to justify a miracle associated with the deceased, in order to facilitate his canonisation (which was carried out by Pope Victor III in 1087). In 1997, two Irish authors proposed an extract from an Irish chronicle as a European sighting of the supernova.[5] This chronicle indicates the following for 1054 : “A round circle of fire was seen at Ros Ela on the Sunday of the feast day of Saint George over five hours during the day, and countless black birds passed before it, in the centre of which there was a larger bird [...] ” The date of the event corresponds to 24 April,[NB 6] long before the sighting noted by the Chinese. The astronomical nature of the account remains very uncertain, and it could simply be mystical in nature, like the previous documents. The location in the sky of the event in question (if it is real) is not mentioned. The time of the event is also not known, but it seems that the event only happened on one day and not for a longer period as would have been the case for a sighting of the supernova. Additionally, the reference to birds strongly suggests an object with some kind of angular extension. An interpretation as a solar halo or aurora depending on the time of the sighting (day or night) also seems more probable, if it is in fact an astronomical event that was described. In 1969, two Armenian authors published a list of accounts of meteor sightings from Armenian chronicles.[11] One of the authors stated some years later that one of the documents could correspond to a sighting of the supernova of 1054.[12] According to his translation of the document, it indicates : “ 1054, the fifth year of the reign of Leo IX. That year, a star appeared on the disc of the moon. This happened on 14th May, in the first part of the night. ” This brief description strongly suggests a closening or concealment of a planet or bright star by the moon. In fact, calculations indicate that on the date mentioned, the moon got closer by around 3 degrees, when Cancer was in conjunction with Jupiter, a fact which the theorists advocating a sighting of the supernova failed to verify or even mention.[NB 7] Among the six European documents, one does not seem to correspond to the year of the supernova (the chronicle of Jacobus Malvecius). Another (the Cronaca Rampona) has large dating and internal coherence problems. The four others are relatively precisely dated, but contradict the Chinese documents : they date from Spring and not Summer 1054, that is to say before the conjunction between the supernova and the sun. Three of the documents (the chronicle of Jacobus Malvecius, the Cronaca Rampona and the Armenian chronicle) make reference relatively explicitly to conjunctions between the moon and stars, of which one is identified (Jupiter, in the Armenian chronicle). Calculations indicate that the moon never got significantly close to the supernova in Spring 1054. The three other documents are very unclear and have almost unusable astronomical content, if it is even real. None of the documented phenomena lasted very long (half an hour in the Church of Oudenberg's account, five hours in the Irish annals and an undetermined, but explicitly short, duration in Albertus' account). No document stipulates the region of the sky where the phenomena took place, and there were no indications as to when the sightings occurred. Supposing the phenomena described have a real physical base, numerous atmospheric phenomena could be the cause. In a more general manner, these documents are not actually astronomical, but produced by learned chroniclers who had limited astronomical knowledge. This is evident in the most workable document, the Armenian chronicle, where the usual conjunction between the moon and Jupiter is not recognised as such, as is the case for numerous other conjunctions.[NB 8] In 1999, George W. Collins and his colleagues proposed a radical reinterpretation of the European documents and claimed that they convincingly indicate that the Europeans had seen the supernova well before Chinese astronomers.[6] Concerning the Chinese documents, they point out their various date errors (see above) as proof that the quality of their observations was inferior to what is commonly accepted, and therfore that nothing rules out the possibility that more hardened observers may have seen the supernova beforehand. They also make their point by bringing up the problem of the localisation of the supernova in relation to the star ζ Tauri (see below). Finally, based on a controversial translation of the document from khitan people, they claim that the supernova was probably visible at the time of the solar eclipse of 10 May 1054.[13] In the opposite way, they reinterpret the European documents as relatively corroborating in relation to the fact that a notable astronomical event occurred in Spring 1054, before the conjunction between the supernova and the sun. They believe that the metaphoric aspect of certain documents only reflects the observers' limited knowledge of the sky, without prejudicing their ability to observe., Furthermore, they claim that the date problems in the Cronoca Rampona are not errors, as the European chroniclers are not intersted in being very precise concerning dates. They also mention, without further elaboration, that the Chinese observations of guest stars was primarily of an astrological, and not scientific, nature, which could make their content biased. As for the reference to the supernova in d'Ibn Butlan scripture, they trust the date of 445 in the Muslim calendar (23 April 1053 — 11 April 1054) and not 446 (12 April 1054 — 1 April 1055) to confirm that the supernova was visible from April 1054, without taking into account the fact that other parts of the scripture are more coherent with the date of 446, not 445. The works of Collins et al. were strongly criticised by F. Richard Stephenson and David A. Green, who pointed out a lack of seriousness in the analysis of their colleagues.[7] Notably, they insist that date problems in Asian documents are easily resolved. One of them (the Xu Zizhi Tongjian Changbian) corresponds in a relatively obvious way to a typographic error, and the other (the month of observation of Japonese documents) to a common date error in this set of documents. They mention that claiming that the supernova was visible at the time of the solar eclipse on May 10th, 1054 is based on an innapropriate interpretation of the translation and is contrary to astronomical reality. In fact, this eclipse having only been partial, no star close to the sun could have been seen at that time. Finally, they insist on the lack of astronomical knowledge of the European chroniclers compared to the Chinese atronomers. According to them, this point makes it difficult to attribute these documents to an observation of the supernova. If this was the case, it would be necessary to explain why no European document mentions the supernova in Summer, when it was perfectly visible according to the Chinese documents, and how the more experienced Chinese and Japonese observers could have missed the supernova at this time. They also note that even in the case of a concordance of dates, nothing proves that events which occurred in the same year correspond to a single astronomical phenomenon. The guest stars of 837 are an example of two different novas which occurred in the same year (additionally marked by the spectacular passing of Halley's comet). The four guest stars of 1592 reinforce this comment. Green and Stephenson's conclusions add to previous works dating from 1995 where the different European observations had already been rejected due to their lack of precision and the impossibility to draw clear astronomical sense from them.[14] The thesis of Collins et al. was not broadly taken up in scientific literature afterwards,[NB 9] but has nevertheless enjoyed a certain visibility to the general public, notably being taken up by the magazine Ciel & Espace[15][16] with a certain enthusiasm. Two Native American paintings in Arizona show a crescent moon located next to a circle that could represent a star.[17] It has been proposed that this represents a conjunction between the moon and the supernova, made possible by the fact that, seen from the Earth, the supernova occurred in the path of the Ecliptic. This theory is compatible with the datings in these paintings. In fact, on the morning of 5 July, the moon was located in the immediate proximity of the supernova, which could reinforce the idea that it was this proximity that had been represented in these paintings. This interpretation cannot be confirmed. The dating of the paintings is extremely imprecise (between the 10th and 12th century), and only one of them shows the crescent moon with the correct orientation in relation to the supernova. Moreover, this type of drawing could well represent a proximity of the moon with Venus or Jupiter.[18][19][20][21] Another, better known document was updated during the 1970s at the Chaco Canyon site (New Mexico), occupied around 1000 AD by the Anasazi. On a vertical surface plane of a construction, it represents a hand, below which there is a crescent moon facing a star at the bottom-left. On the ground in front of the petroglyph there is a drawing which could be the core and tail of a comet. Apart from the petroglyph, which could represent the configuration of the moon and supernova on the morning of 5 July 1054, this period corresponds to the apogee of the Anasazi civilisation. It seems possible to propose an interpretation of the other petroglyph, which, if it is more recent than the other one, could possibly correspond to the passing of Halley's Comet in 1066. Although plausible, this interpretation is impossible to confirm and does not explain why it was the supernova of 1054 that was represented, rather than the supernova of 1006, which was brighter and also visible to this civilisation. The most precise indications of the localisation of the event make reference to a Chinese constellation (asterism in Western astronomical science) called Tianguan by Chinese astronomers. The constellations (asterisms) of Chinese astronomy are generally smaller than the constellations of the western world, and some of these named "asterisms" can consist of a single star. They were catalogued around the 2nd century BC. Depending on the brightness of the stars and their astronomical or symbolic importance, they were more or less well described by the Chinese astronomers, only a part of whose literature has come down to the present day. The asterisms with the brightest stars in the sky were compiled in a work called Shi Shi. Tianguan is a part of it. Its localisation is made relatively easy by the combination of several factors. For the majority of asterisms in Shi Shi, the coordinates of a star in the asterism are given, which generally corresponds to the star which is furthest to the West. In the case of asterisms with only one star, it is enough, in principle, to locate the star. The way in which the coordinates are given by the Chinese astronomers have things in common with the equatorial coordinate system, the equivalent of the longitude and latitude on the celestial sphere, where the poles are determined by the axis of the Earth's rotation, these coordinates are called right ascension and declination respectively in astronomy. The Chinese astronomers noted the angular distance of the star, not in relation to the celestial equator, but in relation to the north celestial pole (which is called the Colatitude in other contexts), along with the brightness in the right ascension not in relation to a reference point (the equinox in modern astronomy), but in relation to a set of reference stars of a particular class of asterisms called the twenty-eight mansions. This kind of measurement was carried out very early for numerous asterisms by Chinese astronomers. It is possible that the composition of a given asterisms can change over time, although this is very rarely made explicit star by star in astronomical reports. This is more likely to happen when the asterism does not consist of bright stars. But the positioning measures for reference stars were made regularly over time because it seems that the Chinese did not think that the skies were unchangeable. They had observed that the relative positions of the stars were susceptible to change, and that the equatorial coordinate system changed over time due to the slow drift in the direction of the axis of rotation of the Earth. This phenomenon, known since Ancient Greece, was discovered independently some centuries later by the Chinese under the name of axial precession. In the case of Tianguan, the position of the asterism was reevaluated some months before the arrival of the guest star. Independent of these new measures, the astronomical reports generally specify the relative position of the asterisms between them. Thus, an asterism is able to be located if its neighbours are robust. In the case of Tianguan, it is indicated that it is located at the foot of the Five Chariots asterism, the nature of which is left in hardly any doubt by representation on maps of the Chinese sky: it consists of a large pentagon containing the bright stars of the Auriga. As Tianguan is also represented to the north of the Three Stars asterism, the composition of which is well known, corresponding to the bright stars of Orion, its possible localisation is strongly restricted to the immediate proximity of the star ζ Tauri, located between “Five Chariots” and “Three Stars”. This star, of medium brightness (apparent magnitude of 3.3), is the only star of its level of brightness in this area of the sky (there is no other star that is brighter than an apparent magnitude of 4.5 within 7 degrees of ζ Tauri), and therefore the only one likely to figure among the asterisms of “Shi Shi”. All of these elements, along with some others, allow “Tianguan” to be confirmed beyond doubt as corresponding to the star ζ Tauri. “Guest stars” reported by the Chinese astronomers correspond to three distinct types of astronomical phenomena: comets, novas et supernovas (and on more rare occasions meteors). The distinction between comets and the others is made by observing whether the star in question moves or not. Over the very long period of observation of the guest star of 1054 (642 days, between the 4 July 1054 and the 6 April 1056), there is no mention of movement, and the very long duration of the phenomenon is three times that of the longest reported duration of a comet (just over six months). The guest star is therefore without a shadow of a doubt a nova or a supernova. The distinction between these two possibilities is made by considering the duration of the phenomenon and its location in the sky. Novæ are explosions which occur on the surface of certain stars, from which the curve of light fades very rapidly, rarely lasting longer than a few months. Even though longer novæ do exist (one of four guest stars of 1592 is probably an example), they are relatively rare. In addition, novæ are less bright phenomena than supernovæ. A nova that is visible in the daytime comes from a star that is close to the sun, where the position in the sky is relatively insecure. By contrast, supernovæ are a lot more rare, and even though they are visible to the naked eye in our Galaxy, they are generally a lot further away, in the centre of the spiral arm, meaning that they are seen from Earth in the galactic plane, in other words, in the bright band which is characteristic of our Galaxy. The guest star of 1054, having a very long period of visibility and being situated on a very weak galactic latitude, presents all the characteristics of a supernova. In order to be able to prove this assertion, what is left of the explosion, meaning the associated supernova remnant, needs to be found. The region of ζ Tauri is location in the opposite region to the Galactic Center. It is there that the depth of the disc of our Milky Way is the shallowest, and therefore the area where there are the least supernovæ. In fact, there are only very few identified remnants of supernovas in this area.[NB 10] If we centre the research on the star ζ Tauri, there is a remnant located in the immediate proximity: the Crab Nebula. There is no other remnant within 5 degrees of it. The closest, SNR G180.0-1.7, has a pulsar PSR J0538+2817 in the centre of it, whose characteristic age is hundreds of thousands of years, and the remnant itself has a considerable angular size (3 degrees). Such characteristics indicate an old object.[NB 11] The Crab Nebula is the only object which presents the expected characteristics of a young remnant and is therefore considered to the product of the explosion which was observed in 1054. Three Chinese documents indicate that the guest star was located “perhaps a few inches” South-East of Tianguan. Song Shi and Song Huiyao stipulate that it “was standing guard” for the asterism, corresponding to the star ζ Tauri. The “South-East”orientation has a simple astronomical meaning, the celestial sphere having, like the Earth's globe, both north and south celestial poles, the “South-East” direction thus corresponding to a “bottom-left” location in relation to the reference object (in this case, the star ζ Tauri) when it appears at the South. However, this “South-East” direction has long left modern astronomers perplexed in the context of this event: the logical remnant of the supernova corresponding to the guest star is the Crab Nebula, but it is not situated to the southeast of ζ Tauri, rather in the opposite direction, to the northwest. The term “perhaps a few inches” (ke chi cun in the Latin transliteration) is relatively uncommon in Chinese astronomical documents. The first term, ke, is translated as “approximately” or “perhaps”, the latter being currently preferred. The second term, chi, means “several”, and more specifically any number between 3 and 9 (limits included). Finally, cun resembles a unit of measurement for angles translated by the term “inch”. It is part of a group of three angular units, zhang (also written chang), chi (“foot”) and cun (“inch”). Different astronomical documents indicate without much possible discussion that a zhang corresponds to ten chi, and that one chi corresponds to ten cun. The angular units are not the ones used to determine stars' coordinates, which are given in terms of du, an angular unit corresponding to the average angular distance travelled by then sun per day, which corresponds to around 360/365.25 degrees, in other words barely one degree. The use of different angular units can be surprising, but it is hardly different to the current situation in modern astronomy, where the angular unit used to measure angular distances between two points is certainly the same as for declination (the degree), but is different for right ascension (which is expressed in angular hours; an angular hour corresponds to exactly 15 degrees. In Chinese astronomy, right ascension and declination have the same unit, which is not the one used for other angular distances. The reason for this choice to use different units in the Chinese world is not well known. However, the exact value of these new units (zhang, chi and cun) was never stipulated, but can be deduced by the context in which they are used. For example, the spectacular passing of Halley's comet in 837 indicates that the tail of the comet measured 8 zhang. Even if it is not possible to know the angular size of the comet at the time it passed, it is certain that 8 zhang correspond to 180 degrees at the most (maximum visible angle on the celestial sphere), which means that one zhang can hardly exceed 20 degrees, and therefore one cun cannot exceed 0.2 degrees. A more rigorous estimation was made from 1972 on the basis of references of minimal separations expressed in chi or cun between two stars in the case of various conjunctions.[22] The results suggest that one cun is between 0.1 and 0.2 degrees and that one chi is between 0.44 and 2.8 degrees, a range which is compatible with the estimations for one cun. A more solid estimation error is that it is generally accepted that one chi is in the order of one degree (or one du), and that one cun is in the order of one tenth of a degree. The expression “perhaps a few inches” therefore suggests an angular distance in the order of one degree or less. If all the available elements strongly suggest that the star of 1054 was a supernova, and that in the area next to where the star was seen, there is a remnant of a supernova which has all of the characteristics expected of an object that is around 1000 years old, a major problem arises: the new star is described as being to the South-East of Tianguan, while the Crab Nebula is to the North-East. This problem has been known since the 1940s and has long been unsolved. In 1972 for example, Ho Peng Yoke and his colleagues suggested that the Crab Nebula was not the product of the explosion of 1054, but that the true remnant was to the South-East, as indicated in several Chinese sources. For this, they envisaged that the angular unit cun corresponds to a considerable angle of 1 or 2 degrees, meaning that the distance from the remnant to ζ Tauri was therefore considerable. Aside from the fact that this theory does not account for the large angular sizes of certain comets, expressed in zhang, it comes up against the fact that there it does not make sense to measure the gap between a guest star and a star located so far away from it, when there are closer asterisms that could be used. In their controversial article (see above) Collins and his colleagues make another suggestion [6]: on the morning of July 4th, the star ζ Tauri was not bright enough and too low on the horizon to be visible. If the guest star, which was located close to it, was visible, it is only because its brightness was comparable to Venus. However, there was another star, brighter and higher on the horizon, which was possibly visible, for reference: Beta Tauri (β Tauri). This star is located at around 8 degrees north-north-west of ζ Tauri. The Crab Nebula is south-south-east of β Tauri. Collins et al. suggest therefore that at the time of its discovery, the star was seen to the south-east of β Tauri, and that as the days passed and visibility improved, astronomers were able to see that it was in fact a lot closer to ζ Tauri, but that the direction “south-east” used for the first star was kept in error.[NB 12] The solution to this problem was suggested (without proof) by A. Breen and D. McCarthy in 1995.[14] and proved very convincingly by D. A. Green et F. R. Stephenson[NB 13] The term “stand on guard” obviously signifies a proximity between the two stars, but also means a general orientation: a guest star “standing on guard” for a fixed star is systematically located below it. In order to support this theory, Green and Stephenson investigated other entries in Song Shi, which also includes reference to “standing on guard”. They selected entries relating to conjunctions betweens the stars identified and planets, of which the trajectory can be calculated without difficulty and with great precision on the indicated dates. Of the 18 conjunctions analysed, spreading from 1172 (the Jupiter-Regulus conjunction on 5 December) to 1245 (the Saturn-Gamma Virginis conjunction on 17 May), the planet was more to the north[NB 14] in 15 cases, and in the three remaining cases, it was never in the south quadrant of the star. In addition, . F. R. Stephenson and another colleague, David H. Clark had already highlighted such an inversion of direction in a planetary conjunction: on 13 September 1253, an entry in the astronomical report Koryo-sa indicated that Mars had hidden the star to the south-east of the twenty-eight mansions sign Ghost (Chinese constellation) (Delta Cancri), while in reality, it approached the star north-west of the asterism (Eta Cancri)[23][clarification needed]. In modern times, the star of 1054 was identified as a supernova between the 1920s and the 1940s. In 1921,Carl Otto Lampland was the first to announce that he had seen changes in the structure of the Crab Nebula.[24] This announcement occurred at a time when the nature of the nebulas in the sky was completely unknown. Their nature, size and distance was subject to debate. Observing changes in such objects allows astronomers to determine if 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 a a few years, while such changes are possible if the size of the object does not exceed a few light-years.[NB 15] Lampland's comments were confirmed some weeks later by John Charles Duncan, an astronomer at the Mount Wilson Observatory. He benefitted from photographic material which has not changed since 1909 and in fact made the comparison with older snapshots easy, highlighting a general movement of expansion of the cloud. The points were moving away from the centre, and did so faster as they got futher freom the centre.[25] Also in 1921, Knut Lundmark compiled the data for the “guest stars” mentioned in the Chinese chronicles known in the West.[26] 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 the French astronomer Jean-Baptiste Biot around the middle of the 19th century, helped by his son, sinologist Édouard Biot. 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,'[27] 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 occured 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 precisely to an explosion dating from the start of the second millennium.[NB 16] Hubble therefore deduced, correctly, that this cloud was the remains of the explosion which was observed by Chinese astronomers.[28] Hubble's comment remains relatively unknown as the physical phenomenon of the explosion was not known at the time. Eleven years later, when the fact that supernovæ are very bright phenomena was highlighted by Walter Baade and Fritz Zwicky[29] and when their nature was suggested by Zwicky[30] Nicholas Mayall proposed that the star of 1054 was actually a supernova,[31] 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.[32] 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 section Compilation of Historic Accounts 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 supernovæ 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. SN 1054 has been involved several times, sometimes fortuitously, in the history of astronomy.[NB 17] Its remnant, the Crab Nebula, was one of the first to be discovered in 1731 by John Bevis. In 1757, Alexis Clairaut reexamined the calculations of Edmund Halley and precicted the return of Halley's comet in late 1758 (more precisely, he predicted it would pass the perihelion in Spring 1759, with the start of its period of visibility some months earlier).[NB 18] It is in searching in vain for the comet that Charles Messier found the Crab nebula, which he at first thought to be Haley's comet. After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet. Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, in order to avoid incorrectly cataloging them as comets.[NB 19] William Herschel observed the Crab nebula numerous times between 1783 and 1809, but we do not know whether he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. After several observations, he concluded that it was composed of a group of stars. In 1844, William Parsons was the first to sketch the cloud, which he named the “Crab Nebula” from 1848. Although the appearance of the drawing is more suggestive of an insect than a crustacean, the term “Crab” was quickly accepted. In 1913, when Vesto Slipher registered his spectroscopy study of the sky, the Crab nebula was again one of the first objects to be studied. The American astronomer noticed its unique characteristics immediately. Changes in the cloud, suggesting its small extent, were discovered by Carl Lampland in 1921.[24] That same year, John Charles Duncan demonstrated that the remnant is expanding,[25] while Knut Lundmark noted its proximity to the guest star of 1054, but did not mention the comments of his two colleagues. In 1928, Edwin Hubble proposed associating the cloud to the star of 1054 (see above), an idea which remained confidential until the nature of supernovae was understood, and it was Nicholas Mayall who indicated that the star of 1054 was undoubtedly the supernova whose explosion produced the Crab Nebula. The search for historical supernovae started at that moment: seven other historical sightings have been found by comparing modern observations of supernova remnants with astronomical documents of past centuries. The oldest historical supernova sighting identified, SN 185, dates from the end of the 2nd century AD. In the 1960s, due to the prediction and discovery of pulsars, the Crab nebula again became a major centre of interest. It was then that Franco Pacini predicted the existence of a neutron star for the first time, which would explain the brightness of the cloud. This neutron star was observed shortly afterwards in 1968, a shining confirmation of the theory of the formation of these objects at the time of certain supernovae. The discovery of the Crab pulsar, and the knowledge of its exact age (almost to the day) allows for the verification of basic physical properties of these objects, such as characteristic age and spin-down luminosity, the orders of magnitude involved (notably the strength of the magnetic field), along with various aspects related to the dynamics of the remnant. The particular role of this supernova to the scientific understanding of supernova remnants was crucial, as no other historical supernova created a pulsar whose precise age we can know for certain. The only possible exception to this rule would be SN 1181 whose supposed remnant, 3C58, is home to a pulsar, but its identification using Chinese observations from 1181 is sometimes contested. Crab Nebula Notes ^ The interesting part of the Latin text says (Latin) stella clarissima in circuitu prime lune ingressa est, 13 Kalendas in nocte initio References ^ SEDS, Supernova 1054 - Creation of the Crab Nebula
Retrieved from "http://en.wikipedia.org/"
|
|
