Heavenly Stems and Earthly Branches
The ten upper characters of a saju (heavenly stems), the twelve lower ones (earthly branches), and the 60 gapja made by pairing them.
Heavenly stems: the ten upper characters
The heavenly stem is the upper character of a pillar and is taken to represent the energy of heaven. There are ten of them; each pair shares one element, and within a pair one is yang and the other yin. Each comes with the image commonly used for it when it becomes the Day Master (일간).
| Character | Reading | Yin-yang | Element | Image |
|---|---|---|---|---|
| 甲 | 갑 | Yang | Wood | a tall, straight tree |
| 乙 | 을 | Yin | Wood | soft grass and vines |
| 丙 | 병 | Yang | Fire | the bright sun |
| 丁 | 정 | Yin | Fire | a warm candle or lamp |
| 戊 | 무 | Yang | Earth | a dependable big mountain |
| 己 | 기 | Yin | Earth | fields that raise grain |
| 庚 | 경 | Yang | Metal | hard rock or raw iron |
| 辛 | 신 | Yin | Metal | a sparkling jewel or a blade |
| 壬 | 임 | Yang | Water | the wide sea or a great river |
| 癸 | 계 | Yin | Water | moist rain and dew |
Earthly branches: the twelve lower characters
The earthly branch is the lower character of a pillar and represents the energy of the earth, the seasons and the hours. The twelve animals we call the zodiac animals (띠) are exactly these branches. Months change at the solar terms, so the months in the table below are approximate.
| Character | Reading | Animal | Element | Season (solar calendar) | Hour |
|---|---|---|---|---|---|
| 子 | 자 | Rat | Water | Midwinter (about December) | 23:00–01:00 |
| 丑 | 축 | Ox | Earth | Late winter (about January) | 01:00–03:00 |
| 寅 | 인 | Tiger | Wood | Early spring (about February) | 03:00–05:00 |
| 卯 | 묘 | Rabbit | Wood | Spring (about March) | 05:00–07:00 |
| 辰 | 진 | Dragon | Earth | Late spring (about April) | 07:00–09:00 |
| 巳 | 사 | Snake | Fire | Early summer (about May) | 09:00–11:00 |
| 午 | 오 | Horse | Fire | Midsummer (about June) | 11:00–13:00 |
| 未 | 미 | Goat | Earth | Late summer (about July) | 13:00–15:00 |
| 申 | 신 | Monkey | Metal | Early autumn (about August) | 15:00–17:00 |
| 酉 | 유 | Rooster | Metal | Autumn (about September) | 17:00–19:00 |
| 戌 | 술 | Dog | Earth | Late autumn (about October) | 19:00–21:00 |
| 亥 | 해 | Pig | Water | Early winter (about November) | 21:00–23:00 |
The hours are not clock time but time based on the sun at the place of birth. For details, see the time adjustment in the article "The Four Pillars: Year, Month, Day and Hour".
The 60 gapja
Pairing the stems and branches one by one in order gives 60 combinations, starting at 甲子 (gapja) and ending at 癸亥 (gyehae). Yang pairs only with yang and yin only with yin, so there are 60 combinations rather than 120. Year names also come round every 60 years, and this is where the name hwangap (환갑) comes from: the 61st birthday, when the name of the year you were born in returns.
Hidden stems (지장간): energy hidden inside a branch
Each branch is taken to hide the energy of between one and three stems. These are called hidden stems (지장간). For example, 寅 (in) holds 戊 (mu), 丙 (byeong) and 甲 (gap), and the most central of them, the main qi (정기), is 甲. Hidden stems show less on the surface, and they are read as traits that appear depending on the situation.