One pillar, two characters
The sexagenary cycle is not one more calendar set beside our own: it is the way Chinese astrology names time. Every unit, a year, a month, a day, receives a name made of two characters. A heavenly stem first, an earthly branch second. That pair is called a pillar, and the reading order never varies.
Jia Zi, the first of the list, joins the first stem to the first branch. The fifty nine that follow are built the same way, moving both series one notch forward at each step.
A word of caution about the names, because romanisation traps hurried readers. The fifth heavenly stem and the seventh earthly branch are both written Wu in pinyin although they correspond to two different and unrelated Chinese characters. A pillar is not guessed from a name heard somewhere: it is calculated.
Why sixty and not one hundred and twenty
Ten stems multiplied by twelve branches give one hundred and twenty possible pairs. The system keeps only sixty of them, and that is not an arbitrary cut.
The two series do not pair up freely. A Yang stem combines only with a Yang branch, a Yin stem only with a Yin branch. Polarity has to stay consistent inside a single pillar, which rules out exactly half of the combinations from the start. You will never come across a pillar mixing a Yang stem with a Yin branch, or the reverse: those pairs do not exist in the system.
Sixty valid pillars, then, not one more. That figure is not a tradition we bow to for want of anything better, it is what is left once the polarity rule has been applied.
The lowest common multiple of ten and twelve
There is a second way of reaching the same number, and it is purely arithmetical. Picture two wheels turning together: the one with ten stems and the one with twelve branches, each moving one notch at every step.
After ten steps the wheel of stems is back at its starting point, but the wheel of branches is not. After twelve steps it is the other way round. It takes sixty steps for the two to find themselves at their initial position at the same time, because sixty is the lowest common multiple of ten and twelve. At the sixtieth step the cycle closes and Jia Zi comes back. In the meantime the series of stems will have completed six full turns, the series of branches five.
That mechanism is where the apparent coincidence between polarity pairing and the period of the cycle comes from. The two lines of reasoning, the polarity one and the lowest common multiple one, end at the same result.
The anchor point: 2 February 1984
A cycle turning without end is useless as long as we do not know where we stand inside it. An anchor is needed, that is to say a date whose pillar is known and from which everything else follows.
The calculation used here is anchored on 2 February 1984, a day carrying the pillar Jia Zi, the first of the sixty. Any other date follows from it: you count the days elapsed since the anchor, you move both wheels that many notches, and you read the pillar obtained. There is nothing mysterious about the procedure, it is positional arithmetic.
That anchor is not a display detail. Changing the reference date would shift the whole cycle, and therefore every pillar calculated. This is why it is fixed once and for all in the calculation engine rather than left to the reader’s choice.
Where the cycle is read in a chart
The cycle does not only serve to date. The four pillars of a chart, the year one, the month one, the day one and the hour one, are four points of that same cycle, taken at four different scales. Their eight characters, four stems and four branches, are the eight characters of BaZi.
Each Da Yun decade is also a pillar of the cycle. The long periods of a life are no different in nature from the birth pillars: they move along the same wheel, simply more slowly, one notch per ten year slice.
Finally, every day of the year carries its own pillar. That makes it possible to place a day in relation to a chart without changing tool or vocabulary. One single mechanism applied at different speeds: that is what gives the system its internal consistency.
What the cycle is not
A pillar is not an omen. The sexagenary cycle is a numbering system before it is an object of interpretation: it says where we stand, not what is going to happen.
Nor is it read through the animal alone. The branch is only half a pillar, and a pillar is only a quarter of the chart. The year animal, the one everyone knows and readily mistakes for the whole of Chinese astrology, occupies only one position out of eight.
Keywords
- One pillar: a stem, then a branch
- Sixty valid pairs, not one hundred and twenty
- Yang with Yang, Yin with Yin
- Sixty, the lowest common multiple of ten and twelve
- Calculation anchor: 2 February 1984, pillar Jia Zi
- One cycle for the pillars, the decades and the days
