1. On the meaning of do in the account of SN 1054.

Both in Meigetsuki and in Ichidai Yoki, the position of SN 1054 is described as "in do (du in Chinese pronunciation) of Shi (Xi) and Sin (Shen)". Do literally means "degree", but in Japanese astronomical records, do was seldom accompanied by numerals, which should be the case if do was used as the unit of angle. Do is usually used in the form of "in do of [the name of the lunar lodge]", e.g., "comet appeared in do of the lunar lodge Bi (Wei; the tail of Scorpion), near the constellation Kansaku (Guansuo; Corona Borealis)".

According to the Chinese theory of Bunya (Fenye, which means field or realm), the celestial sphere was divided into strips of lunar lodges (see vertical lines in the image of the previous page), and each strip corresponded to each province in the domain of China. If a temporal object appears in a strip of a certain lunar lodge, the object was considered to foretell the event in the corresponding province. In this divination, only the right ascension mattered, and the declination was neglected. So it is possible that the expression of "in do of [the name of the lunar lodge]" reflect this theory, though such expression is never found in China. In case of the account of SN 1054, two lunar lodges, Shi (Zui) and Sin (Shen) were mentioned, maybe because the strip of Shi (Zui) is too narrow to disentangle from the adjacent lunar lodge (in the image of the previous page, the strip of Shi (Zui) becomes almost a double line).
So do in this context almost lost the literal meaning of degree, and can be translated as "in the same right ascension as that of".

2. On the relationship between the account of SN 1054 in Meigetsuki and that in Ichidai Yoki

The accounts of SN 1054 are found not only in Meigetsuki, but also in Ichidai Yoki (which means "summary chronicle of each reign"), a chronicle compiled by an unknown author at a time of the emperor Gouda (AD1267- 1324), which was later than the death of Teika (AD 1241), and enlarged later. The account of SN 1054 in Ichidai Yoki is almost the same as that in Meigetsuki, but their relationship is unclear, so I try to shed light on this topic.

It could be that the author of Ichidai Yoki copied the account in Meigetsuki. But comparing the account of other guest stars, some description (e.g., that of AD 1166, it was actually a comet) in Ichidai Yoki are much detailed than that of Meigetsuki. So not all the accounts of guest stars in Ichidai Yoki were copied from Meigetsuki. Moreover, in Ichidai Yoki there are not accounts of guest stars which appeared in AD 1181 (a supernova), AD 1230 (a comet which inspired Teika to get guest star list), and AD 1234 (a comet; there is a contemporary account in Meigetsuki). So the account of guest stars in Ichidai Yoki end up with that of AD 1166 (comet), much earlier than in Meigetsuki, while Ichidai Yoki was written later than Meigetsuki.

In Ichidai Yoki, there are only two accounts of solar eclipse, one account of a meteor, and one account of "red light" (aurora). On the contrary, there are 59 accounts of comets and seven accounts of guest stars. Comparing with other historical sources, the astronomical records in Ichidai Yoki are strongly biased to comets and guest stars. For example, in Meigetsuki there are five accounts of solar eclipse, 28 accounts of lunar eclipse, 27 accounts of occultation and the close encounter between planets and fixed stars, compared with 13 accounts of comets and guest stars (each appearance in the guest star list is counted separately). If astronomical records in Ichidai Yoki were based on other chronicles or diaries, such bias would not emerge.

So it is considered that the sources of comets and guest stars in Ichidai Yoki were a comet list and a guest star list. The last account of comet in Ichidai Yoki is the one of AD 1273, while that of guest star is much earlier (AD 1166), as pointed out above. Comets appeared frequently, so the author of Ichidai Yoki might be able to get the later list. On the other hand, guest stars appeared less frequently, so it is possible that the author got only the guest star list which was written nearly one hundred years before the compilation, e.g., the one written when a guest star (comet) appeared in AD 1181 (the newly appeared one is not included in a guest star list). This hypothesis can explain the strong bias of astronomical records to comets and guest stars in Ichidai Yoki, the lack of later accounts of guest stars in Ichidai Yoki, and the similarity and difference between the description in Meigetsuki and that in Ichidai Yoki, namely, two guest star lists were written separately from the original record in the bureau of Onmyo (the one used in Ichidai Yoki might be earlier), and the extent of detail depended on each copier to some extent when they copied original records to make lists.

There are three textual corruptions in the account of SN 1054 in Ichidai Yoki, which are not seen in Meigetsuki. If the above hypothesis is correct, the corruptions might happen because the author of Ichidai Yoki, unfamiliar with astronomical terminology, made an error when he copied records from the guest star list. On the other hand, in both Meigetsuki and Ichidai Yoki, the month of the appearance of SN 1054 was said to be the fourth lunar month. But in the fourth lunar month, SN 1054 could not be seen by the glare of sun, so "forth" should be "fifth". This error might be in the original record in the bureau of Onmyo, and propagated to the two lists.

2004.11.18 Japanese version 1.0
2006.6.12 English version 1.0
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