Yun Period (Yuan Yun) 元運 · 三元九運 Glossary
The 180-year clock of Xuan Kong feng shui: three eras （三元） of nine periods （九運） of 20 years each. Period 9 began at Lichun 2024 and runs to 2043.
Yuányùn · 元运 (simplified) · 元運 (traditional) · Sānyuán jiǔyùn 三元九運
Source credibility (S/A/B/C/X): S A Rule computability (A/B/C): A for the San Yuan table; the Two-Element Eight-Period yearly table is unverified and not shipped
What it is
Xuan Kong feng shui treats time as a 180-year cycle of nine 20-year periods, each governed by one of the nine stars occupying the centre palace of that era's charts. The periods group into three eras of 60 years — upper, middle and lower yuan （上元／中元／下元） — making the full "three yuan, nine periods" （三元九運） cycle. The current table, independently confirmed against two published sources, runs: Period 1 from 1864, Period 2 from 1884, Period 3 from 1904, Period 4 from 1924, Period 5 from 1944, Period 6 from 1964, Period 7 from 1984, Period 8 from 2004, and Period 9 from 2024 to 2043; the next upper-yuan Period 1 begins in 2044.
Two boundary details matter. First, the period changes at Lichun, shared with the BaZi year-pillar boundary — not at January 1st, so charts for early 2024 before Lichun still belong to Period 8. Second, the period number is what enters the centre palace when the flying-star chart is built; it is the time axis of the whole Xuan Kong Flying Star system.
School differences
Not every lineage keeps this clock. The Tan Yangwu line replaced the three-yuan structure with a "two-element eight-period" system （二元八運） whose year divisions differ; however, no reliable yearly table for it has been located in the project's collation, so it is marked unverified and cannot ship as a rule set until sources are obtained and checked. Different schools also differ on how annual and monthly star cycles key off the period system. See the School Dispute Register for the project's parallel-presentation method.
How this engine computes it
- The San Yuan Jiu Yun table (1864–2043, with the next cycle to 2103) is A-grade kernel data, confirmed against two independent published tables.
- Period switching is tied to the computed Lichun instant from the engine's solar-longitude pipeline, keeping the period, the year pillar and the month pillar on one time base.
- The period system is a ruleset parameter (
yun_system):sanyuan_jiuyunis the default; the two-element variant exists as a configuration slot and is flagged experimental until its yearly table is source-verified. - Period boundaries are covered by the golden-set tests: a sample at the 2024 Lichun instant asserts the switch from Period 8 to Period 9 to the minute.
Related entries
Xuan Kong Flying Star · Nine Stars · Year Pillar (Lichun boundary) · San Yuan vs San He
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