Calendar Reform 历法改革｜ English ｜ 中文 ｜ 栏目索引
Overview. This thread of notes follows a single question: which day does a year begin on? In Chinese history the answer has been changed more than once. The page is arranged as question → evidence → present state, not by date of writing.
1 · Where the question starts: a year-beginning is not a natural thing
Today, saying “the first day of the first month is the first day of the year” sounds self-evident. It is not a natural starting point but a rule that has been fixed and re-fixed many times. To see this, one first has to know how the months were located.
The old method used the direction pointed to by the handle of the Big Dipper to locate the twelve months. This is called doujian (斗建), also yuejian (月建, “month-construction”). When the handle points to yin (寅), the month is “the month built on yin” (建寅之月); when it points to zi (子), “the month built on zi”. Whichever month is taken as the head of the year is the jianzheng (建正, “the standard first month”).
2 · The evidence: the Three First Months, and the Taichu Calendar
The three dynasties did not use the same year-beginning; taken together they are called the san zheng (三正, “Three First Months”). The Xia took the month built on yin — roughly the present first lunar month — as the head of the year; the Shang took the month built on chou (the twelfth month); the Zhou took the month built on zi (the eleventh month). Qin and the early Han moved to the month built on hai (the tenth month).
In the first year of the Taichu era of Emperor Wu of Han (104 BCE) the Taichu Calendar (太初历) was promulgated. It restored the Xia standard and again took the first month as the head of the year, and later dynasties followed it. The calendar in ordinary use today is the continuation of that line.
Source. The account of the san zheng and the Taichu Calendar above is written from three mutually consistent sources: Xinhua, “Why the first lunar month is called zhengyue” (2019-02-05); China Youth Daily (2022-01-18); and the Shanghai Civil Affairs Bureau, “Why the first lunar month is called zhengyue”. It was committed only after the three had been checked against one another.
3 · Related articles on this site, in reading order
- Three Calendars, Three Kinds of Time (三本历法·三种时间) — why three calendars, and three kinds of time, coexist.
- The First Month Was Not Originally Month One (正月本来不是一月) — how the position of the first month was moved about.
- When Does the Year Turn: at Lichun, or at the First Day of the First Month? — which day the turning should be reckoned by.
- Lichun Is Not a Day; It Is a Second — a solar term is an instant, and how it is fixed to the second.
- Nodes and Breaths: The Two Halves of the Twenty-Four Solar Terms (节与气) — why the twenty-four terms are divided into two halves.
4 · Why this thread deserves separate treatment
Read the five pieces along this thread and one thing becomes clear: “which day the year starts on” is a matter of institutions, not of astronomy. What the heavens do — the solar terms, the new moons — can be computed to the second. Which day counts as the beginning of the year was a human decision, taken in a particular year. Keep the two apart, and much of the argument dissolves.