Jiao (Horn)

Jiao (Horn) is the first of the twenty-eight xiu, the lunar mansions of traditional Chinese astronomy. Each xiu is a segment of the sky marked by a group of stars near the celestial equator, and together they divide the heavens into the belt through which the sun, moon and planets appear to move.

Palace, animal and place in the sky

This mansion belongs to the Azure Dragon of the East, the quadrant of the sky lying toward the east, one of the four symbolic creatures among which the twenty-eight are shared out seven to each. In the later scheme that pairs every mansion with a creature, Jiao is assigned the Crocodile.

The twenty-eight mansions are among the oldest elements of Chinese sky-lore, attested well before the common era and used to track the nightly progress of the moon and to fix the calendar. The system is described here as that documented astronomical and calendrical tradition, from which its astrological uses later grew.

Jiao, the Horn, is the first of the twenty-eight xiu, the lunar mansions of Chinese astronomy through which the Moon passes in its monthly circuit, the Chinese counterpart to the Indian nakshatras and the Arabic manazil, but with its own stars and lore. It opens the eastern palace, the Azure Dragon, which holds the first seven mansions and governs the direction east and the season of spring. As the Horn it marks the dragon's horns, identified with stars in Virgo including bright Spica. In the later astrological tradition each mansion carries an animal totem; Jiao's is the Flood Dragon. These are the conventions of the Chinese astronomical and calendrical tradition, in which the twenty-eight mansions divide the sky along the celestial equator and order the almanac's reckoning of favourable and unfavourable days.

The xiu are attested far earlier than either of the systems they are compared with: Shang dynasty oracle bone inscriptions from around the thirteenth century BCE already record the heliacal rising of the mansion Xin, the Fire Star, used to time agricultural and sacrificial activity, making it one of the oldest individually attested stars in any civilisation's astronomical record. Whether the twenty-eight-fold scheme itself is a Chinese invention that reached India and the Arab world, or a version of an Indian scheme that reached China, or whether all three drew independently on a shared and older source, is genuinely disputed among historians of astronomy; the early Chinese textual and oracle-bone evidence is one of the stronger pieces of data any side of that debate has to reckon with, without settling it.