Celestial Stems

The ten Celestial Stems, sometimes known as Heavenly Stems, are the elements of an ancient Chinese cyclic character numeral system: Jia (甲), Yi (乙), Bing (丙), Ding (丁), Wu (戊), Ji (己), Geng (庚), Xin (辛), Ren (壬), Gui (癸). They were used for dates as early as the Shang Dynasty, and are now used with the twelve Earthly Branches in the Sexagenary cycle. They are associated with the concepts of Yin-Yang and the Five Elements.

People of the Shang Dynasty believed that there were ten suns, each of which appeared in order in a ten-day cycle. The Heavenly Stems were the names of the ten suns, which may have designated world ages as did the Five Suns and the Six Ages of the World of Saint Augustine. They were found in the given names of the kings of the Shang Dynasty. Some historians think the ruling class of the Shang had ten clans, but it is not clear whether their society reflected the myth or vice versa. The associations with Yin-Yang and the Five Elements developed later, after the collapse of the Shang Dynasty.

The Stems are still commonly used nowadays in China in counting systems similar to the way the alphabet is used in English.

Earthly Branches

The Earthly Branches (子丑寅卯辰巳午未申酉戌亥; literally "twelve branches") provide one Chinese system for reckoning time.

This system was built from observations of the orbit of Jupiter. Chinese astronomers divided the celestial circle into 12 sections to follow the orbit of Suìxīng (Jupiter, the Year Star). Astronomers rounded the orbit of Suixing to 12 years.