Horyakureki (Horyaku Calendar) (宝暦暦)
The Horyakureki or Horekireki is a Japanese lunar-solar calendar, formerly used in Japan. It is officially called the Horyaku kojutsugenreki.
Japanese calendar dates are in old lunar calendar style. The Christian Era and dates are in the Gregorian calendar style.
Duration of use
On February 11, 1755, the Horyakureki replaced the Jokyoreki (Jokyo calendar), and was used for 43 years until February 16, 1798.
On February 16, 1798, it was reformed to the Kanseireki (Kansei calendar).
Knowing that the rekiho (method of making calendars) used by the Qing dynasty (the Jikenreki; known in English as the Chinese calendar) was, in fact, based on Western calendrical methods introduced by Jesuit missionaries, Yoshimune TOKUGAWA, the then Seii taishogun (literally, great general who subdues the barbarians), decided to adopt a new calendrical system by introducing Western astronomy with all Christian influence removed, and in accordance with Yoshimune's wishes, Masayoshi NISHIKAWA and Noriyoshi SHIBUKAWA began preparations to reform the calendar. However, because of the untimely sudden death of Yoshimune and the lack of the bakufu (Japanese feudal government headed by a shogun) Tenmongata's influence on the politicians inside the government, Yasukuni TSUCHIMIKADO, Onmyo no kami in Imperial Court (Onmyoryo or bureau of Divination) (see the Tsuchimikado family of the Abe clan (from the Muromachi period to the Meiji period)) took initiative in reforming a new calendar.
As a result, the rekiho of the Horyakureki completed by him was inferior to that of the Jokyoreki; for instance, the official calendar missed the prediction of the solar eclipse on October 7, 1763, which was indicated by many astronomers, such as Shuei ISONAGA in Satsuma Province, Munezane KAWATANI in Tosa Province, Tosato NISHIMURA, and Yosho SOGABE in Kyoto, Yasusuke TOITA, Yorimitsu OTSUKA, and Tsuzo TAKAHASHI in Sendai Province, including Goryu ASADA.
For this reason, the bakufu demanded Bunjiro SASAKI to correct the flaws in the calendar in 1764, and then the revised calendar (revised Horyakureki) was used in 1771.
However, that revised Horyaku calendar also developed many flaws such as the occurrence of 'leaping months without a chuki (a midpoint of a setsu (12 divisions of a year))' in 1773, in 1775 and in 1786, which the Chijunho (a calendar technique of setting leap month and leap day) could never theoretically account for.