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Charting the Chinese sky
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WHILE the Greek astronomers Hipparchus and Ptolemy were cataloguing the stars as
seen from the Mediterranean and dividing them into the patterns that we still
know today, Chinese astronomers were developing a completely different
celestial tradition in the far east. If China can be said to have an equivalent
of Ptolemy and the star catalogue in the Almagest, it would be Chen Zhuo (c. 220–280 AD) and the unnamed star list that he compiled. Chen himself post-dates
Ptolemy by a century and a half, but in his catalogue he collated observations
by Chinese astronomers who worked several centuries before him, earlier even
than the Greek Hipparchus.
As in the west, different sets of constellations were invented by different
astronomers, although in China the final selection was fixed much earlier. Chen’s catalogue was a synthesis of the work of three previous authorities and their
respective followers: Shi Shen and Gan De, who both lived around 300 BC; and Wuxian (or Wu Xian), whose dates are completely uncertain and who might
even have been fictional. Shi Shen and his school is credited with 93
constellations, Gan De with 118 and Wuxian with 44, giving a total of 255.
Most of these constellations consisted of only a handful of stars, and some were
just a single star; very few of the ancient Chinese constellations contained
more than a dozen stars. There were no later additions to the Chinese
constellation pantheon after Chen’s time, although some of the existing ones were modified.
Lunar mansions
Additional to these 255 star groups, and predating them, were 28 ancient
divisions of the ecliptic known as xiu (formerly transliterated as hsiu), or mansions, as listed in the table below. These were vertical strips of sky
that acted as markers for following the monthly progress of the Moon, like a
kind of zodiac, thereby providing the basis for a lunar calendar. Since the
names of these mansions are so old, the origin and meaning of many of them is
no longer understood.
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 1464 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.
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 was drawn in the late 14th century, constellation shapes had become so stylized
as to be almost meaningless astronomically.
NEXT:
© Ian Ridpath. All rights reserved
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