How is the chronology of heavenly stems and earthly branches calculated?

The calculation process is as follows:

1, Ten Days of Work has 10 words, and 10 years is a cycle. Include a, b, c, d, e, f, g, Xin, n and d;

2. "Twelve Earthly Branches" has the word 12, and the period is 12 years. Including: Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai.

3, 10 and 12, the least common multiple in mathematics is 60, that is, 60 is not only the reincarnation of heavenly stems, but also the reincarnation of earthly branches.

4. Any word in the heavenly stems can be combined with any word in the earthly branches. * * There are 10 groups, and each group has 12. According to the mathematical arrangement and combination, there should be a combination of * * 120.

5. In the chronology of heavenly stems and earthly branches, the heavenly stems must be placed in front and the earthly branches must be placed behind, which excludes the combination of earthly branches in front and heavenly stems in the back. So only half of the combination of 120 meets the requirements, that is, 60. This is why the heavenly stems and earthly branches Chronology takes 60 years as a cycle.

In addition, in ancient times, people's life span was not long, and most people lived around 60 years old. Therefore, 60 years as the cycle number of chronology is very suitable, corresponding to the life span of people, so people living to 60 years old are also called 60 years old. But 120 is too long as the periodic unit of chronology.

Extended data:

Sixty jiazi

In ancient China, heavenly stems and earthly branches was used as the method to calculate the year, that is, each heavenly stems and earthly branches was paired in a certain order without repetition, which was used as the code of the year. Put a word in the front "heavenly stems" and a word in the back "earthly branches", thus forming a pair of stems and branches.

"Tiangan" starts with the word "A" and "Dizhi" starts with the word "Zi", and the following combinations can be obtained: Jiazi, Yechou, Bingyin, Ding Mao, Chen Wu, Keith, Wu Geng, Xin Wei, Renshen, Gui You, JOE, Yihai, Bingzi and so on.

Shen Jia, Yi You, Bing Xu, Ding Hai, Woods, Xin Chou, Geng Yin, Xin Mao, Ren Chen, Gui Si, Wu Jia, Yi Wei, Bing Shen, Ding You, the Reform Movement of 1898, Ji Hai, Geng Zi, Xin Chou, Ren Yin, Gui Mao, Chen Jia and Yi Si.

From Jiazi to Guihai, * * * 60, and then the cycle starts from Jiazi. Therefore, this method of calculating the year is also called "Sixty Jiazi".

References:

Baidu Encyclopedia-Chronology of heavenly stems and earthly branches