Overview
Key data
| Item | Detail |
|---|---|
| Period of use | 619 – 665 CE |
| Compilers | Fu Renjun, Cui Shanwei |
| Innovation | First use of dingshuo |
| Year head | Jian-yin |
Reform at the founding of the Tang
At the founding of the Tang the Wuyin calendar was promulgated in 619 CE, made by Fu Renjun with Cui Shanwei, and named for its epoch. It was the first calendar promulgated throughout the empire — the Tang had succeeded the Sui, and its calendar ran through the realm.
The true new moon
The true new moon (dingshuo) is found by computing the actual conjunction month by month, as against the mean new moon (pingshuo) computed from the average synodic month. The Wuyin calendar was the first to use dingshuo — the third great reform. Prediction of eclipses grew more accurate with it.
At first the change met objection, when several months in a row gave “three long and three short” against traditional practice; the mean new moon was briefly restored and then the true one reinstated — a sign of how hard reform was.
Afterwards
It was used until 664 CE, when Li Chunfeng’s Linde calendar replaced it.
Compiled and arranged by Chujia Kuang.