Four Pillars
A set of one Heavenly Stem and one Earthly Branch is taken from the year, month, day, and hour of birth, forming four sets totaling eight characters, hence it is also called the Eight Characters (Ba Zi).
Convert the year, month, day, and hour of birth into a set of Heavenly Stem and Earthly Branch each, stack the four sets to get a total of eight characters; this is the 'Eight Characters (Ba Zi)'.
In each pillar, the Heavenly Stem is on top and the Earthly Branch is on the bottom. The boundary rules for the four pillars are all different, which is where mistakes are most easily made:
- The Year Pillar is bounded by Li Chun (Start of Spring), not the first day of the lunar calendar. Those born before Li Chun are still counted in the previous year.
- The Month Pillar is bounded by the twelve 'Jie' (major solar terms, such as Li Chun, Jing Zhe, Qing Ming...), so a leap month in the lunar calendar does not affect the Month Pillar.
- The Day Pillar follows the continuous cycle of the sixty Jiazi, uninterrupted by the change of year or month.
- The Hour Pillar is derived from the Day Stem, so if the Day Pillar is wrong, the Hour Pillar will definitely be wrong as well.
⚠️ The Year and Month Pillars align with the exact moment of the solar terms, while the Day and Hour Pillars use the local clock time of the birthplace. Using the same time for all four pillars is the most natural way to write it, but it is incorrect.