Su Song Star Map 2 - Public domain geographic map

Traditional Chinese astronomy has a system of dividing the celestial sphere into asterisms or constellations, known as "officials" (Chinese 星官 xīng guān). The Chinese asterisms are generally smaller than the constellations of Hellenistic tradition. The Song dynasty (13th-century) Suzhou planisphere shows a total of 283 asterisms, comprising a total of 1,565 individual stars. The asterisms are divided into four groups, the Twenty-Eight Mansions (二十八宿, Èrshíbā Xiù) along the ecliptic, and the Three Enclosures of the northern sky. The southern sky was added as a fifth group in the late Ming Dynasty based on European star charts, comprising an additional 23 asterisms. The Three Enclosures (三垣, Sān Yuán) include the Purple Forbidden Enclosure, which is centered on the north celestial pole and includes those stars which could be seen year-round, while the other two straddle the celestial equator. The Twenty-Eight Mansions form an ecliptic coordinate system used for those stars visible (from China) but not during the whole year, based on the movement of the moon over a lunar month.