Rat

The Rat is the first of the twelve animals of the Chinese cycle, paired with the first of the twelve earthly branches, zi. The branches are the older layer: a set of twelve cyclical signs used in China for counting days from at least the Shang oracle-bone period, combined with the ten heavenly stems to produce the sixty-term cycle by which years, months, days and double-hours are all reckoned.

The zi branch governs the double-hour around midnight, between eleven at night and one in the morning, the point at which the day turns over, and it is associated with the water phase and the direction north. The animal is read for quickness, resourcefulness, thrift and an alertness that shades into wariness. The pairing of animal to branch, not the animals themselves, is what makes the system work: the branch supplies the position in the cycle and the correspondences, and the animal is its emblem.

The familiar story that the Jade Emperor held a race and that the rat won by riding on the ox's back and jumping off at the finish is a folk tale, widely told and much loved, but it is a later explanation of an order that already existed rather than its cause. What the twelve-year cycle rests on historically is the branch system, and its correlation with animals is attested in the Qin-period bamboo manuscripts from Shuihudi, dating to the third century BCE, in a day-book that gives animals for the branches in an order close but not identical to the modern one.

The twelve-year length itself matches the sidereal period of Jupiter, about 11.86 years, which Chinese astronomy tracked as the Year Star, Suixing, and this is generally taken as the origin of a twelve-part division of the years. The system is shared, with local variation in the animals, across China, Korea, Japan, Vietnam, Mongolia, Tibet and Thailand.

Sources Chinese Mythology: An IntroductionAnne Birrell with Chinese Mathematical Astrology: Reaching Out to the StarsHo Peng Yoke