In ancient China, astronomy was a state-sponsored activity, and astronomers were members of the imperial bureaucracy. The demands of the emperor included the construction of accurate calendars and the keeping of a complete record of celestial events. Because detailed histories were produced for each dynasty, we have an unusually complete record of the activities of Chinese astronomers. As in Babylonian astronomy, the Chinese relied on arithmetical-algebraic procedures to study the motions of the Sun, Moon, and planets. As in Greek astronomy, the Chinese developed an explicit cosmology and used geometry—albeit of a very elementary sort—to determine some of the numerical constants of the model. Chinese cosmology in the sense of a spatial physical conception of the celestial world was more primitive than its Greek counterpart and never played much of a role in the primary subject of calendrical astronomy.
Both astronomy and cosmology reached a certain level of maturity during the Han Dynasty. We have the treatise Zhou bi suan jing, which dates from the first century b.c., one of the earliest surviving Chinese scientific works and one that has been closely studied by modern scholars. There is also a treatise on cosmology, the Ling xian, written around 100 a.d. by the great Han astronomer, Zhang Heng.
During the Han age an older cosmology, the Gai tian, gave way to the Hun tian, the latter remaining the dominant cosmology for the following centuries. The Gai tian, or "Doctrine of the Heaven as a chariot-cover" (Cullen 1996, 35), is described in the Zhou bi suan jing. It posited a flat, stationary Earth beneath the heavens, the latter rotating rather like a large umbrella about a point on the surface of the Earth. The rising and the setting of the Sun was explained as an optical phenomenon that resulted as the Sun merged in the distance with the horizon. The Hun tian, which is set out in the Ling xian, replaced the chariot cover by a sphere. The heavens revolved as a sphere on an axis inclined to the flat base of the Earth in much the same way that the skies revolve about the auditorium floor of a planetarium. The celestial sphere became the fundamental astronomical concept, and coordinates on this sphere were used to locate the positions of celestial objects.
In addition to the Gai tan and Hun tian, there was a third cosmology in early China, the Xuan Ye. According to this view, the planets moved through empty space without the assistance of mechanical spheres. Despite its somewhat modern-looking outlook, the Xuan Ye represented a general and indefinite conception of the cosmos and never played a role in the study of astronomy.
The Chinese understanding of cosmology encompassed much more than the simple geometrical modeling of the motion of the planets. In all of the stages of its development Chinese thinking was informed by a belief in the organic unity of the universe, in the existence of various correlations or resonances between the earthly and celestial worlds. The numerical schemes employed to describe the solar-lunar calendar and the motions of the planets were influenced by a priori assumptions derived from a kind of numerological astrology. For example, ancient Chinese astronomers believed that the number five was special and that all things could be described in terms of five phases. The number five was the number of the wandering stars that accompanied the Sun and the Moon in their cyclical journeys through the heavens. Other numerical relations of cosmological significance were taken from the I Ching, the Book of Changes, a work that emphasized the balancing of opposites, of the yin and the yang, a dynamical process that was believed to be pervasive in the universe.
Astrology was much more integrated into Chinese astronomy than was the case in Babylonian and Greek astronomy. In the latter its role was largely that of an external agent that provided formal motivation to develop accurate planetary and eclipse tables. The actual construction of these tables followed empirical and theoretical principles that used observation and (in the case of the Greeks) geometric modeling, influenced, to be sure, by abstract philosophical beliefs about the mathematical nature of reality. By contrast, in Han China, numerical harmonies rooted in astrology influenced the selection of the cycles of numbers at the foundation of calendrical astronomy.
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