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Semmyō calendar (Semmyō-reki) — Japanese lunisolar system derived from Xuanming li

Semmyō-reki, also called Semmei-reki or Xuanming li, was a Chinese-derived Japanese lunisolar calendar used from the late 9th century until the late 17th century for official, agricultural, and religious timekeeping.

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The Semmyō calendar (Japanese: Semmyō-reki; often written Semmei-reki) is a historical Japanese lunisolar calendar derived from the Chinese Xuanming li. Introduced into Japan in the classical period, it served as the principal municipal and court calendar from the late 9th century until it was superseded in the late 17th century. The system is typically described as part of the broader family of genka-type calendars adopted in East Asia.

Characteristics

As a lunisolar calendar, Semmyō reconciled lunar months with the solar year. Months were based on successive new moons, and intercalary (leap) months were inserted periodically so that the calendar remained roughly aligned with seasonal solar markers such as solstices and equinoxes. Calculations for month lengths and intercalation were based on astronomical rules and tables that had been transmitted from Chinese sources.

History and development

The underlying mathematical and astronomical ideas trace back to the Chinese Xuanming li, and the system was adapted to Japanese administrative needs over centuries. Court astronomers and calendar specialists maintained and adjusted the system when discrepancies accumulated. The Semmyō calendar's long use reflects both its practical utility and the conservatism of premodern timekeeping institutions.

Uses and social importance

  • Official scheduling: dates for imperial edicts, taxation, and legal deadlines.
  • Agricultural guidance: timing of planting, harvesting and seasonal work tied to solar terms.
  • Religious and social festivals: assigning ritual days, shrine observances, and seasonal celebrations.
  • Astrology and divination: choosing auspicious dates for ceremonies or public projects.

Transition and notable facts

Over time, accumulated inaccuracies and the availability of new astronomical knowledge prompted calendar reform. In the late 17th century Japanese scholars introduced a revised system that replaced Semmyō-reki for official use. For more on the name and variants see Semmyō-reki and for background on the Chinese model see Xuanming li. The Semmyō calendar remains important to historians studying premodern Japanese administration, agriculture, and ritual life.

Questions and answers

Q: What is the Semmyō calendar?

A: The Semmyō calendar, also known as Semmei-reki or Xuanming li, was a Japanese lunisolar calendar.

Q: When was the Semmyō calendar used?

A: The Semmyō calendar was used from the late-9th century to the late-17th century.

Q: How does the Semmyō calendar work?

A: The Semmyō calendar is a lunisolar calendar, which means it combines both lunar and solar cycles to determine dates.

Q: What distinguishes the Semmyō calendar from other Japanese calendars?

A: The Semmyō calendar was one of the oldest and longest-lived Japanese calendars.

Q: Why was the Semmyō calendar important in Japan?

A: The Semmyō calendar played an important role in Japanese society, as it was used to determine auspicious dates for various events and ceremonies.

Q: Was the Semmyō calendar used only in Japan?

A: No, the Semmyō calendar is also known as Xuanming li in Chinese and was used in China during the Tang dynasty.

Q: Is the Semmyō calendar still used today?

A: No, the Semmyō calendar has been replaced by the Gregorian calendar in modern Japan.

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