Shi, the Encampment of the Black Tortoise

Shi, the Encampment, is the thirteenth of the twenty-eight xiu and the sixth mansion of the northern palace, the Black Tortoise. Its name means an encampment or house, identified with two bright stars of the Great Square of Pegasus. In the later astrological tradition its animal totem is the Pig. As one of the twenty-eight lunar mansions it marks a portion of the Moon's path. These are the conventions of the Chinese astronomical and calendrical tradition, in which the twenty-eight xiu divide the sky into four palaces of seven mansions, the mansion the Moon occupies on a given night contributing to the almanac's reckoning of whether the day favours building, travel, ceremony, or rest.

Shi's identification with two bright stars of the Great Square of Pegasus, Markab and Alpheratz in the modern Western naming, gives this mansion the same underlying stars the Arabic tradition uses to define its own paired stations Al Fargh al Mukdim and Al Fargh al Thani a short distance apart in that system's count, so the Great Square supplies reference points independently reused by the Chinese, Arabic and, more loosely, Hellenistic fixed-star traditions for marking this same stretch of the fixed autumn sky.