What is heavenly stems and earthly branches?

Used to arrange years and dates in the summer calendar.

Heavenly stems and earthly branches, the main branch for short, originated from the observation of astronomical phenomena in ancient China.

Ten cadres refer to meeting, understanding, softness, strength, harmony, slaughter, chapter, weight, metaphysics and yang.

Twelve branches refer to those who are trapped, enthusiastic, nurturing, single-handed, promising, wilderness, escaping, thanking, wading in the beach, having difficulties, being alone, and being extremely deep.

Simplified heavenly stems and earthly branches: "A, B, C, D, E, Ji, G, Xin, Ren, Gui" is called ten heavenly stems, and "Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai" is called twelve earthly branches.

Ten heavenly stems and twelve earthly branches are matched 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 has far-reaching influence, and he still uses heavenly stems and earthly branches in calendar, tricks, calculation, naming and so on.