Overview
Key data
| Item | Detail |
|---|---|
| Nature | The first chapter of the Book of Documents, one of the Five Classics |
| Date of composition | Very early in origin; the received text was edited in later hands |
| Core passage | The section beginning “He charged Xi and He to reverence the vast heaven” |
| Key ideas | The four mid-season stars and months; the year of three hundred and sixty-six days; intercalation to fix the seasons |
The observation of the four mid-season stars
The canon records Yao’s charge to Xi Zhong, Xi Shu, He Zhong and He Shu to go to the four places — Yanggu, Mingdu, Meigu and Youdu — and observe the stars of each quarter, thereby fixing the middle of each season.
The stars recorded are “the star Bird at the equinox,” “the star Fire at the longest day,” “the star Xu at the other equinox” and “the star Mao at the shortest day” — the four mid-season stars.
This is the earliest set of stellar observations in Chinese literature, long prized in archaeoastronomy.
The four mid-season months and seasons
Each of the four stars goes with one mid-season month: the spring equinox, the summer solstice, the autumn equinox, the winter solstice.
The four seasons are fixed from these, giving the year four fixed points.
“A year of three hundred and sixty-six days”
The chapter gives the year as “three hundred and sixty-six days,” with an intercalary month to complete the seasons.
It is among the earliest statements in Chinese literature of the length of the tropical year: three hundred and sixty-six days by round number, with “intercalation to fix the seasons” the means of reconciling lunations with the solar year.
Value
The passage binds astronomical observation, the division of the seasons and the method of intercalation into one account: the starting point of Chinese astronomical and calendrical literature. Later treatises on the calendar habitually begin their account of origins with it.
The twenty-four solar terms took shape by stages: first the two solstices, then the two equinoxes, then the four “beginnings,” then a division into eight nodes, and only then into twenty-four terms. The complete names and order of the twenty-four terms first appear in the “Treatise on Astronomy” of the Huainanzi.
Compiled and arranged by Chujia Kuang.