Jōkyō calendar

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

The Jōkyō-reki system was developed and explained by Shibukawa Shunkai. He that the length of the solar year is 365.2417 days.

Shirakawa discovered errors in the traditional Chinese calendar, the Semmyō calendar, which had been in use for 800 years.