What are the Heavenly Stems and Earthly Branches?
The Heavenly Stems and Earthly Branches are two sets of Chinese counting signs, ten stems and twelve branches. Paired in order they make sixty names, the sexagenary cycle, used for years, months, days and hours. The branches carry the twelve zodiac animals, and the stems carry the five elements.
Counting to sixty
The ten heavenly stems (tiangan) run Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui. The twelve earthly branches (dizhi) run Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai. The first name is Jia-Zi, the second Yi-Chou, and so on, both lists stepping forward together. 1,2
After ten steps the stems run out and start again while the branches carry on, so the eleventh name is Jia-Xu. The two lists only come back into step after sixty, their lowest common multiple. An odd stem always meets an odd branch, which is why there are sixty pairs and not 120. 1
What it counts
Years are the famous use, but the same sixty names have numbered days, months and hours, and divided the horizon into sixty sectors of 6° each. Temples sometimes keep sets of sixty statues, one god for each year of the cycle. 1
Each branch carries an animal, which is how the zodiac attaches to the calendar. Each pair of stems carries an element, which is where a "Wood Dragon" or "Fire Horse" year gets its element. 2024 was Jia-Chen, the Wood Dragon; 2026 is Bing-Wu, the Fire Horse. 3,4
Chinese fortune-telling reads the stem-branch pairs of a birth year, month, day and hour, eight characters in all, and weighs which pairs agree or clash with others. 1
How the machine works it out
Calculated facts only, worked out the same way the machine does it.
- Year in the cycle: (Chinese year − 4) mod 60, counting the year from Lunar New Year. 1984 began a new cycle with Jia-Zi, the Wood Rat.
- Stem from the last digit of the year: 4 Jia, 5 Yi, 6 Bing, 7 Ding, 8 Wu, 9 Ji, 0 Geng, 1 Xin, 2 Ren, 3 Gui.
- Element pairs: Jia and Yi wood, Bing and Ding fire, Wu and Ji earth, Geng and Xin metal, Ren and Gui water.
Where the idea comes from
Era by era, with sources. More in the Reading Room.
- Ancientc. 1300–1050 BCEShang kings' oracle bones date divinations by days of the sixty-day cycle; one turtle plastron asks about rain on a Jia-Chen day. 5,6
- Classicalc. 2,000 years agoStem-branch names come into use for years, a practice the Hong Kong Observatory puts at more than two thousand years old. 2,7
- Modern1984The current sixty-year cycle begins on 2 February 1984. 7
- Today2018The Hong Kong Observatory explains why it changes the year name at Lunar New Year rather than at the solar term Spring Commences. 2
Common misconceptions
“There are 120 stem-branch pairs.” Only sixty occur, because the two lists step forward together. 1
“The cycle was invented for the zodiac.” It is a counting system older than the animals, first used for days. 5,8
Questions people ask
Sources
- Heaven Stems and Earth Branches, University of California San Diego (David K. Jordan). Read on .
- What year is it today?, Hong Kong Observatory. Read on .
- Lunar New Year 2024: What does the Year of the Dragon mean?, The University of Sydney. Read on .
- Lunar New Year 2026: the Year of the Horse, The University of Sydney. Read on .
- Oracle bone collection (Or 7694/1506-2125), British Library. Read on .
- Inscribed Plastron Ping 0063, Museum of the Institute of History and Philology, Academia Sinica. Read on .
- Lunar New Year: dates, animals and the zodiac, Royal Museums Greenwich. Read on .
- Set of twelve zodiac animals, The Metropolitan Museum of Art. Read on .