Shichen: the twelve double hours, and the animal your birth time carries

The neatest thing about the twelve hours is that the Chinese did not always have them, and did not name them by branches for a long time after they did. The scholar who worked this out was Gu Yanwu, in the seventeenth century, in a short entry of his Rizhilu headed "the ancients did not divide the day into twelve," and his argument is simply a stack of quotations in date order.

First the Zuozhuan, the great chronicle of the fifth century BC, in which a diviner explains that "the sun has ten numbers, so there are ten hours," matching the day to the ten heavenly stems rather than the twelve branches. Then Du Yu, the third-century commentator on that chronicle, who "took it as twelve hours" and gave them their names, midnight, cockcrow, daybreak, sunrise, mealtime, mid-morning, noon, sun-slant, afternoon meal, sunset, dusk, people-settled, "without setting up the twelve branches as headings." Then the Han histories, one after another: a rebellion that broke through the siege "at dusk," a battle "from daybreak to mealtime," troops drawn up "at cockcrow," an earthquake "at the early meal." Every one of them dates the event by the name of the hour, and not one of them by its branch. Then the Huainanzi of 139 BC, which divides the sun's day not into twelve at all but into fifteen stations, from Dawn-Bright where it bathes in the pool of the east to Fixed-Dusk where it enters the valley of the west, "which Yu made into morning, day, dusk and night."

Gu's conclusion is a sentence long: "the Han did not yet call midnight the zi hour," and he adds that he does not know who first did. The double hours, in other words, are a Han institution and the names are farm names; the branch labels that make them part of the stem-and-branch machine, and therefore part of a bazi chart, came later and silently. For a system whose whole appeal is its antiquity that is worth knowing, and it is worth knowing that the Chinese scholarly tradition knew it first.

Every English explainer of the zodiac hours has a story for each animal: the rat is busiest at midnight, the ox chews its cud before dawn, the tiger hunts in the small hours, the rabbit comes out at sunrise, the dragon brings the morning rain, and so on round to the pig asleep at ten. They are pleasant and they are all modern. The pairing of animal to branch is at least nineteen hundred years old, and the text that records it attaches no hour to any of them.

That text is Wang Chong's Lunheng, written around AD 80, in a chapter arguing with the five-phase theorists of his day. To show that "wood conquers earth" and the rest of the conquest cycle cannot explain which animals eat which, he runs through the branches: "yin is wood, and its creature is the tiger; xu is earth, its creature the dog; chou and wei are also earth, the ox and the goat," and so on through all twelve, then points out that if the theory held, the rat should chase the horse and the rooster peck the rabbit, which they do not. His point was to embarrass a theory; ours is that the list was already complete, already keyed to the branches, and already familiar enough for a skeptic to use it in an argument, in the first century. The animals belong to the branches; the hours borrowed the branches later; the stories about nocturnal rats were fitted on afterward to explain an order that had another origin. The zodiac pages take each animal on its own.

The clock gives you the branch of your hour pillar directly. It cannot give you the stem, because ten stems and twelve branches do not divide into each other: the sixty stem-branch pairs cycle through the hours in five days, so the stem sitting on any given hour depends on the day. The traditional fix is a rhyme, and the Ming manual Sanming Tonghui quotes it under "deriving the hour from the day": jia and ji days start again from jia; yi and geng days begin with bing; bing and xin start from wu; ding and ren have geng at zi; and where do wu and gui begin? Ren-zi is the true road. Five pairs of day stems, five starting stems for the Rat hour, hence "five rats." From the Rat, the hour stems simply count forward through the ten.

The manual also says why the count starts at zi rather than at dawn: "heaven opened at zi, the season when one yang is first born." Midnight is where the day's yang begins to return, so the day's first pillar is built around it, which is the same logic that centers the Horse on noon. The table is below, rebuilt from the rule; the site checks it against the calculator's own hour pillars every time this page is built, so the two cannot quietly disagree.

Because the Rat hour straddles midnight, a birth between 23:00 and 00:00 is in the zi hour of one day by the clock and, by some reckonings, already in the next day's zi hour. Practitioners have argued for centuries over whether the day pillar should roll at 23:00 with the hour, or wait for midnight, and the two answers give the same person two different day masters. Some schools split the block into a "late zi" belonging to the old day and an "early zi" belonging to the new. Our calculator rolls the day at 23:00, most of the field does not, and the whole disagreement, with eight calculators tested on the same births, is the subject of the conventions page. If your birth time is in that hour, read it before you trust any chart, including ours.

The other correction is the sun. The double hours were built on solar time, with noon in the middle of the Horse, and a modern time zone can put the clock an hour or more off the sun; all of China runs on Beijing time across what would be five zones, so a birth in Urumqi at 13:30 by the clock is still late morning by the sun. The calculator takes an optional birth city and corrects for this before choosing the hour; the methodology page shows the arithmetic.

The Ming manual's image for the four pillars is a plant: the year is the root, the month the shoot, the day the flower, and the hour the fruit, "for without the flower there is no fruit." In the reading, the hour is the last third of life, and children. Mechanically it is a quarter of the material the day master is weighed against, and it is the column most likely to carry one of the special stars a reading names. All of that is why a chart cast without a birth time is called three-pillar and labeled so: the year, month and day stand, the day master is untouched, and the fruit is missing. The reading order walks a real chart with its hour in place, and the finder above will put yours in.