What did Shoushi Calendar / Season-Granting Calendar look like?

A documentary calendar containing precise astronomical parameters: suishi (tropical year), shuoshi (synodic month), qiyin (winter solstice moment), and others.

How did Shoushi Calendar / Season-Granting Calendar work?

Synchronous observations at 27 stations nationwide → data compiled → precisely determined tropical year = 365.2425 days → precisely computed synodic month = 29.530593 days → used cubic interpolation to calculate solar, lunar, and planetary motions.

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《授时历》

Shoushi Calendar / Season-Granting Calendar

A tropical year length of 365.2425 days — identical to the modern Gregorian calendar (1582) but established 301 years earlier.

《授时历

Scientific Principle

Precise tropical year determination; cubic interpolation: solves the non-uniformity of celestial motion. Arc-and-sagitta method: spherical trigonometry formulas.