Overview
Key data
| Item | Detail |
|---|---|
| Period of use | c. 221 – 104 BCE |
| Year head (doujian) | Jian-hai (the tenth month) |
| Type | Quarter-remainder calendar |
| Tropical year | 365¼ days |
| Synodic month | 29 + 499/940 days |
Use and the beginning of the year
The Zhuanxu calendar was adopted after Qin unified the realm and remained in use until the Taichu reform of 104 BCE — some 117 years under the Qin and the early Han. Its year did not begin with the first month but with the tenth month (jian-hai).
One point needs care: making the tenth month the head of the year did not mean calling it the “first month.” The Qin still numbered the months as the tenth, eleventh … first, second … ninth, and the pairing of the four seasons with the months was unchanged. The year head is one thing, the name of the first month another, and the seasonal pairing a third.
Why the tenth month
The choice of jian-hai as year head follows from the epoch from which the calendar was reckoned. The six ancient calendars all used the quarter-remainder method; they differ not in method but in epoch and year head — fix the epoch and the starting point, and the year head follows.
This arrangement lasted into the early Han. The Han kept the Qin system, and the calendar was not changed until the Taichu reform restored the Xia reckoning (jian-yin); thereafter it stood for some two thousand years.
Material evidence
The Zhuanxu calendar itself is long lost, but recent excavations have supplied proof. The day-counts and month names in the Shuihudi Qin bamboo slips allow its arrangement to be tested — the only one of the six ancient calendars with material evidence.
The other five survive only in fragments, scattered through the Han shu and the Kaiyuan Zhanjing; their outlines can be recovered only by reconstruction.
Compiled and arranged by Chujia Kuang.