Heavenly Stem

The ten Celestial or Heavenly Stems (Chinese: ; pinyin: tiāngān) are a Chinese system of ordinals that first appear during the Shang dynasty, ca. 1250 BCE, as the names of the ten days of the week. They were also used in Shang-period ritual as names for dead family members, who were offered sacrifices on the corresponding day of the Shang week. The Heavenly Stems were used in combination with the Earthly Branches, a similar cycle of twelve days, to produce a compound cycle of sixty days. Subsequently, the Heavenly Stems lost their original function as names for days of the week and dead kin, and acquired many other uses, the most prominent and long lasting of which was their use together with the Earthly Branches as a 60-year calendrical cycle.

The Japanese names of the Celestial Stems are based on their corresponding Wu Xing elements, while their Manchu names are based on their respective elements' colors.

The Shang people believed that there were ten suns, each of which appeared in order in a ten-day cycle (旬; xún). The Heavenly Stems (tiāngān 天干) 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 in their Temple Names. These consisted of a relational term (Father, Mother, Grandfather, Grandmother) to which was added one of the ten gān names (e.g. Grandfather Jia). These names are often found on Shang bronzes designating whom the bronze was honoring (and on which day of the week their rites would have been performed, that day matching the day designated by their name). David Keightley, a leading scholar of ancient China and its bronzes, believes that the gān names were chosen posthumously through divination. 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.

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