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Overview
Key data
| Item | Detail |
|---|---|
| Period of use | 1199 – 1206 CE |
| Compiler | Yang Zhongfu |
| Tropical year | 365.2425 days |
| Synodic month | 29.530594 days |
Yang Zhongfu and the Tongtian calendar
The Tongtian calendar was made by Yang Zhongfu, promulgated in 1199 CE. It holds a special place in Chinese calendrical history.
Three contributions
1. A tropical year of 365.2425 days, exactly the value the Gregorian calendar would adopt three centuries later — 383 years earlier.
2. The grand epoch dropped, a near epoch used. Instead of reckoning from a remote epoch, it started near to hand, simpler and with less accumulated error.
3. A varying tropical year. Yang was the first to hold that the length of the tropical year is not constant. He touched the heart of the matter, though he could not give a precise formula — a remarkably early insight.
Assessment
Its eclipse predictions were still imprecise, so it was used only seven years. Yet in the value of the tropical year and in theoretical insight it is the highest achievement of Southern Song calendrical work.
Modern accounts often set it beside the Shoushi calendar as two landmarks in the movement of the traditional calendar toward precision.
Full text
No electronic full text of this work is available here. This calendar has no separate transmitted text; its methods survive scattered in the calendrical treatises of the standard histories. Among the histories held here, see Songshi, Calendrical Treatise, juan 84.
The title, date, summary and index structure compiled here are offered under CC BY 4.0 (attribution: Chujia Kuang · kuangchujia.com).
Compiled and arranged by Chujia Kuang.