Geng

Geng is the seventh of the ten Heavenly Stems (tiangan). Its element is Metal and its polarity is yang, so Geng is glossed as yang Metal, likened in tradition to a sword, an axe, or wrought iron, hard, sharp, and forceful. As one of the ten stems it combines with the twelve Earthly Branches to form the sexagenary cycle of sixty that numbers years, months, days, and double-hours in the traditional calendar. The stems run in fixed order, each bearing one of the five phases in a yang or yin form, and Geng brings the yang aspect of Metal after the two Earth stems. These are the conventions of the Chinese calendrical and cosmological tradition, used in the almanac and in the four-pillars method of reckoning a person's fate.

Geng is the seventh Heavenly Stem, the first of the pair carrying the Metal phase, and as an odd-numbered stem it takes the Yang polarity, traditionally likened to raw ore, a sword blade or an axe, hard and unrefined, in contrast to Xin's Yin Metal, likened to a fine blade or jewellery. In the controlling cycle of the five phases, Metal is checked by Fire and in turn checks Wood, a relationship the tradition reads onto a Geng day master in four pillars (BaZi) astrology as decisive and forceful, sometimes to the point of bluntness, a personality suited to cutting through obstacles rather than negotiating around them. Within the sixty-term sexagenary cycle, Geng combines only with Yang-polarity Earthly Branches: Rat, Tiger, Dragon, Horse, Monkey and Dog. Geng years recur every ten years and, combined with the branch cycle, only every sixty years with the same paired branch, the basis of the traditional Chinese reckoning of a sixty-year lifespan as a complete cycle.

Every stem has a partner among the other nine, and the five pairings, called the combinations of the heavenly stems, are fixed: each stem combines with the one five places away from it. Geng pairs with Yi, and the tradition holds that a combined pair takes on a phase of its own distinct from either stem's native phase. The pairing is used in almanac work and in fate calculation, where a combination in a chart is read as a binding between the two positions that carry it.

The ten stems are older than the sexagenary cycle they now form half of. On the Shang oracle bones of the second millennium BCE they name the ten days of the xun, the Shang week, and Shang kings are known to history by posthumous names built on them, so a stem was a unit of the working calendar before it was a term of cosmological art. The five-phase and yin-yang readings attached to the stems are later, systematised under the Han, and the atlas records the two layers as two layers.

Geng is yang Metal, conventionally the axe, the weapon or the unworked ore against the wrought ornament of Xin. Metal in the five-phase scheme is generated by Earth and generates Water, and it overcomes Wood, which is why the Geng and Yi combination is one of the pairings the almanac treats as consequential.

The stem's own attributes here are Metal and yang polarity. Those two facts fix its place in the run of ten, since the stems proceed through the five phases in generation order taking the yang member first and the yin member second, and they fix how it is read wherever it appears, in the year, the month, the day or the double hour of a Four Pillars chart.

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