Xu

Xu is the eleventh of the twelve Earthly Branches (dizhi). Its zodiac animal is the Dog, its element is Earth, its direction is west-northwest, and its double-hour runs from 7 to 9 pm, the early evening. As one of the twelve branches it combines with the ten Heavenly Stems to form the sexagenary cycle of sixty that numbers years, months, days, and double-hours. The branch names the eleventh animal of the twelve-year cycle and the corresponding month and double-hour, carrying the Dog's loyal and watchful associations in the almanac. These are the conventions of the Chinese calendrical and cosmological tradition, in which the twelve branches order the twelve-year animal cycle, the months, and the twelve two-hour periods into which the day is divided.

Xu is the eleventh Earthly Branch, corresponding to the Dog, and to the double hour from 7 pm to 9 pm, early evening. Its dominant hidden stem is Wu, giving it the Earth phase, with Xin and Ding present as secondary hidden stems. Xu is a Yang-polarity branch, pairing only with Jia, Bing, Wu, Geng or Ren within the sexagenary cycle, and it governs the ninth lunar month and the compound northwest direction. In BaZi astrology a chart with Xu prominent is read through the Dog's traditional associations of loyalty, honesty and a strong sense of justice, sometimes to the point of an inflexible moral rigidity that the tradition treats as the same trait's shadow side. The Dog also appears, alongside the other eleven branch animals, in the widely repeated origin legend of a race called by the Jade Emperor to fix the order of the zodiac, a folk tale first recorded relatively late and not part of the branch system's own ancient textual history.

Beyond the animal it carries, a branch enters three fixed sets of relations that the almanac and the fate-calculation tradition use constantly. Xu belongs to the trio Yin, Wu and Xu, one of the four groups of three branches spaced four apart which are read as combining into Fire. It clashes with Chen, the branch six places away, and it forms one of the six harmonies with Mao. These relations are properties of position in the twelve, not of the animal.

The branches also do more work than the year cycle they are best known for. They divide the day into twelve double hours, so Xu names a period of two hours as well as a year and a month; they mark the twelve directions of the compass, Xu standing at west-northwest; and they carry the twelve stations against which the movement of Jupiter was tracked, which is one proposed origin for the twelve-year cycle itself.

The stem-and-branch day count is the longest continuously running day count known. Numbering days by ganzhi begins in the Shang inscriptions and has run without acknowledged interruption since, through every dynastic change and every calendar reform, because the cycle of sixty is independent of any astronomical quantity and therefore needs no correction. Chinese historical dates from the classical period onward can be checked against it.

Xu closes the autumn in the month assignment and is the last of the four Earth branches to do so before Chou closes the winter. Its clash with Chen sets the two spring-and-autumn Earth branches against each other, and the tradition reads clashes between Earth branches differently from clashes between the cardinal ones, since what is opposed is a transition rather than a season.

Sources Chinese Mathematical Astrology: Reaching Out to the StarsHo Peng Yoke with The Chinese Sexagenary Cycle and the Ritual Origins of the CalendarAdam Smith