Charting the Chinese sky 

Unlike the 12 houses of the zodiac familiar to western astrologers the 28 xiu were not equally spaced but varied considerably in width, from a mere 2° (Zi, the 20th mansion) to 33° (Jing, the 22nd), and stretched from pole to pole. Each xiu was named after a constellation within it, not necessarily on the ecliptic – another difference from western zodiacal constellations, all of which lie on the ecliptic.

Although Chen Zhuo’s original catalogue was lost some time in the 6th century, we know from later works that it contained 1,464 stars, over 400 more than the Almagest. When we talk of the Chinese sky and Chinese constellations, it is this blending of the three traditions of Shi Shen, Gan De, and Wuxian with the 28 xiu of the zodiac that we mean, giving a total of 283 constellations. What’s more, the Chinese system spread to Japan and Korea, so Chen’s catalogue and the maps made from it are the basis of a more general far-eastern tradition. This combined set of constellations remained in use until the early 17th century, when western constellations were introduced by Jesuit missionaries such as Adam Schall von Bell (1592–1666).

Chinese star charts 

When Chinese celestial cartographers came to depict the sky, they at first used different colours to distinguish the constellations of the three different schools. Around AD 440 the Chinese astronomer Qian Lezhi made a bronze celestial globe (some describe it as a planisphere rather than a globe) on which the stars attributed to Shi Shen were shown in red, those of Gan De in black, and those of Wuxian in white (open circles). China was also the source of the first star charts on paper, the oldest known example being the Dunhuang chart, now thought to date from the mid to late 7th century AD.

Since Chinese constellations were symbolic, rather than pictorial as in the West, their member stars were usually not identified with any precision and could change over time. Hence there is considerable variance in the depiction and interpretation of Chinese constellations from different eras. These differences can be confusing and frustrating to anyone trying to reconstruct the Chinese sky.

Adding to the difficulty of identification is that Chinese astronomers made no attempt to convey the relative brightnesses of the stars by the sizes of the individual dots on their charts. This lack of interest in star magnitudes is characteristic of all Chinese (and Korean) star charts, and reveals an uncomfortable truth: they are primarily a canvas for the ruminations of astrologers, rather than a blueprint of the sky for scientific purposes. Chinese Emperors were considered to rule under a mandate from heaven, but this mandate could be revoked if they ruled badly; signs of heavenly displeasure would, it was thought, be seen in the form of celestial phenomena such as eclipses, comets, and ‘new’ stars (novae). So it was important for the Emperor and his advisors to know what such events meant whenever they occurred.

Given the various depictions and interpretations of constellations to be found in Oriental treatises down the ages, it seems that the size and shape of each constellation, as well as its significance, could be moulded at will to suit the requirements of the individual practitioner. By the time this Korean star chart, the Cheonsang yeolcha bunya jido, was drawn at the end of the 14th century, constellation shapes had become so stylized as to be almost meaningless astronomically.