Cause & Context
Accumulated errors in inherited calendars led to inaccurate celestial predictions; Kublai Khan ordered a nationwide astronomical survey to formulate a definitive imperial calendar.
Epochal Overview
Astronomer Guo Shoujing invented 13 advanced instruments, deployed 27 observation stations from Siberia to the South China Sea, and promulgated the Shoushi Calendar, calculating the solar year to 365.2425 days.
Key Figures
Guo Shoujing directed technical innovation alongside mathematicians Wang Xun and Xu Heng, completing calculations within four years.
Civilizational Impact
The Shoushi Calendar served for 363 years—the longest in Chinese history—and matched the accuracy of the Gregorian calendar three centuries before Europe.