Jōkyō calendar

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

The Jōkyō calendar (貞享暦, Jōkyō-reki) was a Japanese lunisolar calendar, in use from 1684 to 1753.[1] It was officially adopted in 1685.[2]


The Jōkyō-reki system was developed and explained by Shibukawa Shunkai,[3] he recognized that the length of the solar year is 365.2417 days.[1]

Shibukawa discovered errors in the traditional Chinese calendar, the Senmyō calendar, which had been in use for 800 years.[3]

See also[edit]


  1. ^ a b Nussbaum, "Jōkyō-reki" at p. 431; "Teikyō-reki" at p. 431
  2. ^ Orchiston, Wayne et al. (2011). Highlighting the History of Astronomy in the Asia-Pacific Region, p. 155.
  3. ^ a b Nussbaum, "Shibukawa Shunkai" at pp. 850–851.

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