Kuo Shoujing (郭守敬, 1231–1316) in the Yun (元) dynasty and was used for more
than 360 years in China (Nakayama 1971).
The Shou-shih calendar was introduced to Japan in around 1670. However, in the
long span of time since its production, there had arisen nonnegligible discrepancies
in calendar time for the prediction of sky phenomena. Shibukawa began to construct
a new calendar based on the Shou-shih calendar by taking into account the difference
in longitude between Japan and China. After observations of solar and stellar
motions for several years, he completed a new calendar system and called it the
Yamato calendar (大和暦). On the other hand, the Tsuchimikado family (土御門家)
of the Imperial Court in Kyoto proposed the adoption of the Daito-reki (大統暦Tat’ung calendar, the calendar in the Ming Dynasty, 明朝).
After a long dispute on the accuracy of these two calendars, the Yamato calendar
was finally accepted and promulgated in 1685 under the name of Jokyo calendar (貞
享暦).
With this achievement, Shibukawa was appointed for chair of Tenmonkata at the
Surugadai Observatory (駿河台天文台) in the city of Edo. After Shibukawa’s
death, this observatory remained inactive for several generations since Tenmonkata
was a hereditary position and no able astronomer was able to replicate Shibukawa’s
works.
1.2.2 Horeki Calendar
In the early eighteenth century the Eighth Shogun, Yoshimune (徳川吉宗,
1684–1751), himself an enthusiastic amateur astronomer, tried to modernize the
calendar, appointing Nishikawa Seikyu (西川正休) as a Tenmonkata in charge of
calendar making. Nishikawa had an outstanding reputation for his knowledge of
Western astronomy.
Nishikawa and his college Shibukawa Noriyoshi (渋川則休) intended to formulate a new calendar based on the Shou-shih calender (授時暦). On the other hand,
Tsuchimikado Yasukuni (土御門泰邦) and his family in Kyoto tried to develop a
new calendar based on the traditional Jokyo calendar. There arose a bitter conflict
between these two groups, and Nishikawa’s group was finally defeated after the
death of Shogun Yoshimune in 1751.
As a consequence, the new Horeki or Horyaku calendar (宝暦) was developed by
the Tsuchimikado family in 1755. However, since Yasukuni did not have sufficient
knowledge of calendar calculation, the essentials of this calendar were the same as
those of the Jokyo calendar. The failure of this calendar became apparent a few years
later when the prediction of a solar eclipse failed. Despite this failure, the calendar
was used for 43 years up to 1797.
During the formation of the Horeki calendar astronomical observations in Edo
were conducted at the Kanda Observatory, Edo. This observatory was shut down in
1757 and temporarily moved to Ushigome in Edo. To promote calendar reform, the
government established a new observatory in Asakusa, in the city of Edo, in 1782.
1.2 Calendar Reforms
3
than 360 years in China (Nakayama 1971).
The Shou-shih calendar was introduced to Japan in around 1670. However, in the
long span of time since its production, there had arisen nonnegligible discrepancies
in calendar time for the prediction of sky phenomena. Shibukawa began to construct
a new calendar based on the Shou-shih calendar by taking into account the difference
in longitude between Japan and China. After observations of solar and stellar
motions for several years, he completed a new calendar system and called it the
Yamato calendar (大和暦). On the other hand, the Tsuchimikado family (土御門家)
of the Imperial Court in Kyoto proposed the adoption of the Daito-reki (大統暦Tat’ung calendar, the calendar in the Ming Dynasty, 明朝).
After a long dispute on the accuracy of these two calendars, the Yamato calendar
was finally accepted and promulgated in 1685 under the name of Jokyo calendar (貞
享暦).
With this achievement, Shibukawa was appointed for chair of Tenmonkata at the
Surugadai Observatory (駿河台天文台) in the city of Edo. After Shibukawa’s
death, this observatory remained inactive for several generations since Tenmonkata
was a hereditary position and no able astronomer was able to replicate Shibukawa’s
works.
1.2.2 Horeki Calendar
In the early eighteenth century the Eighth Shogun, Yoshimune (徳川吉宗,
1684–1751), himself an enthusiastic amateur astronomer, tried to modernize the
calendar, appointing Nishikawa Seikyu (西川正休) as a Tenmonkata in charge of
calendar making. Nishikawa had an outstanding reputation for his knowledge of
Western astronomy.
Nishikawa and his college Shibukawa Noriyoshi (渋川則休) intended to formulate a new calendar based on the Shou-shih calender (授時暦). On the other hand,
Tsuchimikado Yasukuni (土御門泰邦) and his family in Kyoto tried to develop a
new calendar based on the traditional Jokyo calendar. There arose a bitter conflict
between these two groups, and Nishikawa’s group was finally defeated after the
death of Shogun Yoshimune in 1751.
As a consequence, the new Horeki or Horyaku calendar (宝暦) was developed by
the Tsuchimikado family in 1755. However, since Yasukuni did not have sufficient
knowledge of calendar calculation, the essentials of this calendar were the same as
those of the Jokyo calendar. The failure of this calendar became apparent a few years
later when the prediction of a solar eclipse failed. Despite this failure, the calendar
was used for 43 years up to 1797.
During the formation of the Horeki calendar astronomical observations in Edo
were conducted at the Kanda Observatory, Edo. This observatory was shut down in
1757 and temporarily moved to Ushigome in Edo. To promote calendar reform, the
government established a new observatory in Asakusa, in the city of Edo, in 1782.
1.2 Calendar Reforms
3