Glossary entry
Heavenly stems and earthly branches (天干地支)
The stems are ten, the branches are twelve, and every year, month, day and hour in the Chinese calendar is written as one of each — a pair. The chart is built from those four pairs.
The ten and the twelve
Stems: 甲 乙 丙 丁 戊 己 庚 辛 壬 癸, cycling every ten, each belonging to one of the five elements. Branches: 子 丑 寅 卯 辰 巳 午 未 申 酉 戌 亥, cycling every twelve, each covering two hours of the day and each standing for one zodiac animal.
Where they show up
The birth hour pair fixes the palace the chart starts from; the year stem turns four main stars into the four transformations; the branch is what the zodiac lookup and the pairing table work from. The reading itself writes palace and star names, not stems and branches.
Questions
Are the branches the same as the zodiac animals?
Yes — the twelve animals are the everyday names of the twelve branches: 子 the rat, 丑 the ox, and so on round the cycle.
Why sixty years and not 120?
Ten and twelve advance together, so a stem and a branch meet again only after sixty steps. The same pair cannot come back inside sixty years — that is the 六十甲子 cycle.
Zi Wei Dou Shu chart, free See a completed reading first The full glossary