What is heavenly stems and earthly branches?

Heavenly stems and earthly branches, the main branch for short, originated from the observation of astronomical phenomena in ancient China. In ancient China, "A, B, C, D, E, Ji, G, Xin, Ren and Gui" were called "ten days' work"; "Zi, Ugliness, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai" are collectively called twelve branches.

Ten heavenly stems and twelve earthly branches are collocated in turn to form sixty basic units, and they cooperate with each other in a fixed order to form the chronology of the stems and branches. Heavenly stems and earthly branches's invention had a far-reaching impact, and heavenly stems and earthly branches still uses it today for calendars, art numbering, naming and so on. In ancient China, heavenly stems and earthly branches was mainly used to mark the day, month, year and time.

The chronological method of the main branch is to determine the "Moon Building" with the direction of Beidou bucket handle and Beidou bucket handle as the criteria for determining the month, which is called "Fighting Sword", and "Sword" represents the direction of the top of Beidou bucket handle. The circular rotation of the Big Dipper is closely related to the change of solar terms. In different seasons and at different times, the Big Dipper will point in different directions, which has also become the basis for the ancients to judge the seasons, that is, the so-called "bucket handle refers to the east, and the world is spring; Guide to barrel handle, it's summer in the world; Bucket handle refers to the west, and the world is autumn; Bucket handle refers to the north, and the world is winter. ".

Bucket handle, the Big Dipper, rotates east, south, west and north, and is called one year old (Figure). Years old is divided into twelve days (or "December order") in the official calendar, and each month has two solar terms. Bucket handle rotates and points to twelve days in turn, which is called "December Construction". "Building the moon", also known as the moon order, is a way for the ancients to track the moon.