Heavenly stems and earthly branches, date of birth.

In ancient times, the Han people took heaven as their work and the earth as their support. There are ten kinds of heavenly stems, including: A, B, C, D, E, Ji, G, Xin, Man and Ghost. There are twelve earthly branches: Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai. Heavenly stems and earthly branches used to record the sun. Ten heavenly stems and twelve earthly branches are combined into sixty units in turn. Odd aerial stems are matched with odd ground branches, and even aerial stems are matched with even ground branches. From Jiazi to Guihai, there are sixty, which is called Sixty Jiazi. Ancient Han people used this method to record the year, month and day, and so on.

The ancient Han people divided a day and night into twelve hours, one hour is equivalent to two hours in modern times, representing five o'clock and six o'clock in the morning in Shi Mao, and so on. By analogy, these four hours, noon, untimely, Shenshi, Youshi, Qishi, Zishi, Ugly and Yin Shi are all a whole day and night.

Heavenly stems and earthly branches is not only a tool for ancient Han people to calculate the life span of stars, but also a calendar for timing and lettering, which is closely related to the history, culture and daily life of China.