Overview
Key data
| Item | Detail |
|---|---|
| Period of use | 206 – 280 CE (late Han to Wu) |
| Compilers | Liu Hong, Xu Yue |
| Tropical year | 365.2462 days |
| Year head | Jian-yin |
Liu Hong and the Qianxiang calendar
The Qianxiang calendar was made by Liu Hong in the late Eastern Han and completed by Xu Yue. It was not promulgated at first; it was later adopted by Wu and used until 280 CE.
Three advances
1. A more precise tropical year. At 365.2462 days its fractional part fell below ¼ for the first time, closer to the true value than the 365.25 of the quarter-remainder calendar.
2. The moon’s inequality brought in. The uneven speed of the moon (its “hurrying and slowing”) was built into the computation — the forerunner of later lunar tables.
3. The eclipse limit. A criterion for whether a solar eclipse can occur was proposed, giving eclipse prediction a test.
Assessment
Though little used, the Qianxiang calendar was valued by later calendrists — He Chengtian and Yi Xing both drew on it — and marks a turning point from rough to fine reckoning.
Compiled and arranged by Chujia Kuang.