Heavenly Stems and Earthly Branches: China's 60-Cycle System
·2585 words·6 mins
Chinese timekeeping runs on two interlocking sets of signs: ten heavenly stems (天干, tiangan) and twelve earthly branches (地支, dizhi) — together covered by the umbrella term ganzhi (干支), and in older romanizations tien gan dizhi. Neither set is used alone. One stem and one branch, taken in step, form a two-character label — 甲子 jiazi, 乙丑 yichou, 丙寅 bingyin… — and because the two sets have different lengths, the labels run through sixty distinct combinations before returning to the start. That is the Chinese sexagenary cycle: the sixty-term counter that dates years, months, days, and hours on a Chinese calendar, and that supplies all eight characters of a Bazi chart. This page explains the two sets of signs, how the pairing produces sixty terms rather than a hundred and twenty, and where the system actually came from — a story that begins with carved oracle bones, not with books.