What did Zu Chongzhi's Daming Calendar look like?

A documentary achievement, not a physical artifact. A systematic calendrical treatise.

How did Zu Chongzhi's Daming Calendar work?

Long-term astronomical observation → discovery that the winter solstice point shifts westward each year (precession) → corrected the discrepancy between the tropical year and sidereal year → more precise calculation of the twenty-four solar terms and solar/lunar eclipses.

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祖冲之大明历

Zu Chongzhi's Daming Calendar

First to introduce precession into calendrical calculations. The tropical year length was 365.24281481 days (error of only 46 seconds). π was computed to 3.1415926-3.1415927 — a precision not surpassed in the West for a millennium.

祖冲之大

Scientific Principle

Precession: the Earth's rotation axis completes one 26,000-year cycle, causing the vernal equinox point to shift westward along the ecliptic by ~50.26 arcseconds per year. π calculation: method of circle partition (approximation by inscribed polygons).