Time in Japan: Early Recorded Dates

[Bethetsu]

Recently Josh (in http://forums.samurai-archives.com/viewtopic.php?t=5261 )gave a link to an article about a sword found with a early date. http://heritageofjapan.wordpress.com/2011/09/21/
The news made all thepapers here. We have also had a discussion of dates on wooden tablets on this forum.
I decided to start a thread in "Time in Japan" on the calendrical aspects of these early finds. I won't make it a "class" though, partly because I do not know enough, and partly because if it uses news, I cannot make a curriculum. But comments are welcome.

So here is a summary of the calendar aspects of the account.
A sword, apparently made in Japan, was found in a mid-seventh-century tomb in Fukuoka, Kyushu, bearing the inscription
大歳庚寅正月六日庚寅日時作刀凡十二果
大歳(great year-a normal phrase)庚寅(27th cyclic year)正月六日(1st month, 6th day)庚寅日(27th cyclic day)
Based on the inscription, it has been concluded that the sword is dated in 570, and that this shows that Japan was using the Genka Calendar 元嘉暦.
How do you get that conclusion?
Since cyclical years repeat every 60 years, first we must ask how to get 570, especially since the sword was in a 7th-century tomb.

First, one can reasonably assume they had the cyclical year and day correct.
It is also reasonable to assume the date 1/6 is based at least some knowledge of the Chinese calendar--that the month started around the new moon and that the first month was the 2nd (or sometimes 3rd) month after the winter solstice. Now, if the 6th of the month is 27 庚寅, the 1st is 22 乙酉. So let's look at the cyclical dates of the new moon in China for the possible first months--ones starting late Jan.to late Feb. --in 庚寅 Years and see which fall around day 乙酉 22.
(I used http://eclipse.gsfc.nasa.gov/phase/phasecat.html
and
http://maechan.net/kanreki/)

690 2/15 己卯 16
630 1/19 丁酉 34
630 2/18丁卯 4
570 1/22 乙酉 22
570 2/21 乙卯 52
510 1/26 甲戌 41
510 2/24 2月癸卯 40
450 1/29 壬戌 59

As can be seen, the only new moon that comes anywhere close is Jan. 22, 570. That is exactly the New Years' Day for the Genka calendar, as well as two of the three Chinese current calendars (西元570年1月22日 → [Chen (S) ]陳宣帝太建2年(歲次庚寅)1月1日; [N. Qi ]北齊後主武平元年(歲次庚寅)1月1日 [N. Zhou] 北周武帝天和4年(歲次己丑)12月30日 ).
This does not _prove_ of course that they were using the Genka calendar. But it shows they were not using the crescent moon, and since you cannot observe the new moon, it strongly suggests they were using a calendar based on a procedure, not just guessing. Virtually all modern (post WWII) scholars agree that the Genka calendar was the first calendar to be used in Japan, as it was used in Paekche in the 6th century and the Nihon Shiki says it was used in Japan in 692 . So the sword strongly supports the supposition that the Genka calendar was in use in Japan in 570.


"Sakaue said. 'It is the first concrete evidence showing that the Genka calendar spread in Japan following the calendar expert’s visit to Japan [in 554].'” But, of course is it possible that Fukuoka had got a calendar from Paekche independent of any in Yamato?

By the way this article states, "“It is the first time that an item bearing a date based on the Chinese sexagenary cycle has been found in Japan. " (干支の入った確実な日付としては初の発見) Of course, this is a mistake for "this is the earliest item with a firm date using the sexagenary cycle."

"Experts have pointed to the possibility that the Genka calendar had been used in Japan since the era of Emperor Yuryaku in the fifth century." I am very doubtful. There are obviously no artifacts to indicate it. If the "possibility" comes from the Nihon Shoki dates, it is probably a misunderstanding of statements that the Shoki used the Genka calendar for determining the cyclical days starting from around 450, the time of Yuraku. For dates before that it used a simplified version of the current Gihô calendar　儀鳳暦 (麟徳暦).

[nagaeyari]

[Bethetsu]

There are two obvious arguments against the Genka calendar's being used in Japan during Yuuryaku's time. One is that since it was implemented in China only in 445, it would have come to Japan extremely quickly, much faster than any other calendar. Another is that if they had been using the Genka procedure in Japan for a century, why would they have asked for calendar books and experts from Korea in 553?

I have read several papers on the Shoki dates. Almost all of the Shoki 900 some dates give the cyclic day, so one can tell if they match a certain procedure or not.
The modern theory of the Shoki dates is that of Ogawa Kiyohiko. He did his work around 1940 but it was not published till 1978.
Except for some dates generally accepted as transmission errors and three which are debated, the dates match either a simplified version of the Gihô procedure 儀鳳暦 (665 in China, about 697 in Japan), the Genka procedure (445 in China), or (by far the majority) both. The latest date for which only the Gihô procedure is possible is 399, the end of Vol. 11, Nintoku 87冬十月癸未朔己丑; the earliest date for which only the Genka procedure is possible is that of Ankô's death on 三年秋八月甲申朔壬辰 456 at the end of Vol. 13.
So it is arbitrary to say the use of Genka started with Vol. 14--calendrically it could have been 12 or 13-- but 14 is considered likely in view of the editorial style change. I don't know what they do with the last date in Vol. 13. being Genka--perhaps they say it was moved back separately. In any case, the Shoki does not imply that the Genka calendar came to Japan in the reign of Yuryaku.
The standard modern theory is that except for some dates towards the end based on documents that recorded cyclical days, the editors of the Shoki used a simplified version of their current, modern calendar to calculate the cyclic date of early month-day dates (where ever they came from), and the old, Genka calendar for dates sometime in the 5th century on, because that was the procedure that was presumably used to calculate most of those dates in the first place.

Why was the change made between 400 and 456? What hit me was that the Genka procedure took effect during that period, so it would be a reasonable time to change. I can see the editors discussing, "What do we do with dates before Genka?" and deciding to use a version of the Gihô.
This is not to say there was no calendar during the time of Yuryaku: the Saitama Inari sword says 辛亥年七月中, but that is not the same as saying they calculated it by a regular procedure, let alone that all of the dates from the period in the Shoki together with their cyclic days were preserved till 720.