Jōkyō calendar

Jōkyō calendar (貞享暦, Jōkyō-reki), also called Teikyō-reki, was a Japanese lunisolar calendar (genka reki).[1] It was used from 1684-1753.[2] It was made official in 1685.[3]

Jōkyō calendar published in Japan in 1729. Exhibit in the National Museum of Nature and Science in Tokyo.

History

The Jōkyō-reki system was the work of Shibukawa Shunkai.[4] He recognized that the length of the solar year is 365.2417 days.[2]

Shirakawa discovered errors in the traditional Chinese calendar which had been in use for 800 years.[4] This older system was also known as the Semmyō calendar or 'Semmei-reki. It was also known as the Xuanming calendar.[5]

References
  1. Nussbaum, Louis-Frédéric. (2005). "Calendar" in Japan Encyclopedia, p. 98.
  2. Nussbaum, "Jōkyō-reki" at p. 431; "Teikyō-reki" at p. 956
  3. Orchiston, Wayne et al. (2011). Highlighting the History of Astronomy in the Asia-Pacific Region, p. 155; Bramsen, William. (1880). Japanese chronological tables, p. 25.
  4. Nussbaum, "Shibukawa Shunkai" at pp. 850-851.
  5. Nussbaum, "Semmei-reki" at p. 840.

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