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]