What does birthday have to do with heavenly stems and earthly branches?

The earthly branch in the date of birth refers to the earthly branch of 12. This disciple is Zi Chou, Xu Hai at noon in Tatsumi. Birthday is a horoscope composed of heavenly stems and earthly branches. Also known as four pillars, each group has a heavenly stem, a total of eight words, yin is divided into yang, and heavenly stem is yang.