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The Calendar and Hour System - Leinss

Gerhard Leinss (HU Berlin) The calendar and the hour system in Japan: a historical review

Gerhard Leinss (HU Berlin)

The calendar and the hour system in Japan: a historical review


When Japan adopted the continental time order in the seventh and eight centuries, a way of keeping time was introduced, which included the usage of a water clock and a method to sub-divide the day into twelve hours. We do not know much, however, about that system initially applied, and it is only from the tenth century onwards that received texts and extant calendars allow us to reconstruct the time system in which hour were of equal length and announced as such at the Heian court. Thereafter, there were only minor changes to that system and no innovation of any significance in the way time related events were marked on the surface of calendars. This is particularly true for the new calendar formats that emerged from the 13th century onwards, which contain far less time references than the earlier Chinese versions; this suggests that there was not much demand for such kind of information from female members of the aristocracy for whom these new formats written in Japanese script were devised. This lack of entries that relate to the sub-division of the day in calendrical documents continued when in the 14th century printing became the primary method, by which calendars were reproduced to supply larger groups of the population with an annual calendar. It is safe to assume that by the end of the 17th century all groups of society had access to a printed calendar, although these editions were still comparatively void of any time related references. This changed fundamentally in the early 18th century when the bakufu-editors of the standard printed calendar introduced again accurate time related issues such as specifying, among others, the length of day and night and the precise hours for sunrise and sunset at certain days of the year. Prefaces of extant calendar written by the officials reveal however that in that case the hour system used by the astronomers led to conflicts with the time perception that prevailed among the population: they obviously had different ideas about the beginning of the day and the hours which were announced by the time bells differed from those expressed on the surface of the calendar. It was only in the last calendar reform of the pre-modern period in 1844 that the astronomers decided to adjust their time notations to this widespread use of hours that varied in length according to the seasons. From that year onwards, calendar hours and hours struck by the time bells were in tune. However, this situation lasted only 29 years until 1873 when the adoption of the Western time system shifted the hour system back to hours of equal length, thus to that time system, which was maintained during all those centuries by the astronomers on the archipelago who were computing and devising the yearly calendar.