The Purposes of Chinese Astronomy

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The Han dynasty was the 1st to establish imperial rule over a political entity roughly comparable to modern China. It is only from this time that we can discern the establishment of the main outlines of Chinese astronomical and cosmological thinking. According to Sivin (1969), the success of Chinese astronomy as a predictive science owes much to its divorce from traditionalist cosmologies, which, as in the west, tended to restrict experimentation and rethinking. The predictive science in itself was not part of a deductive scheme, except insofar as it occasionally required expedient correctives.

Our knowledge of the astronomy of the period has been considerably increased by the discovery of the burial of a man named Li, the son of the 1st Marquis of Yi in 168 b.c. at Mawandui (or Ma-Wang-tui), Ch'ang-sha, Hunan, with 20 silk books. These included Classics on Stars, which incorporated the writings of the astronomers Gan De (or Kan-te) in his Astronomy, and Shi Shen (Astrological Astronomy or perhaps Astronomical Astrology), written between ~370 and 270 b.c. However, this version of Classics on Stars contained a study of the movements of Jupiter from 246 b.c. to 178 b.c., contemporary with Li. The book gives the synodic and sidereal periods of the planets and contains a catalog of the shapes of comets. The synodic period and sidereal periods for Jupiter are given as 395 105/240 = 395.438 days, and 12 years, respectively; the corresponding numbers for Saturn are 377 days and 30 years, respectively. The configuration information provided for the planet Venus is that it is a visible morning star for 224 days, invisible for 120 days, an evening star for 224 days, and "hides away" for 16 96/240 days = 16.400 days. These values can be compared with the modern values given in §2.4.4 and Table 2.9. Mention is also made of a pre-Han armillary sphere (Ng 1987; Xi 1984, pp. 38-39; Sivin 1981).

Chinese astronomers had several tasks:

(1) to keep track of the calendar; and, related by,

(2) to observe the periodicities of heaven;

(3) to predict eclipses; and

(4) to record the astrological omens—such as unpredicted eclipses and "guest stars," both those with tails (comets) and those without (usually novae and supernovae).

Why were these important? Astronomy in China was driven to provide precision in the timing of events because the political realm had to be in rhythm with the natural one. This is clear from many inscriptions and records, such as the the "instructions" for future emperors drawn up during the Sung Dynasty (see §10.1.7). Chinese Time-Keeping and Calendar

According to Eberhard (1983/1986, p. 54), the calendar was probably lunar originally because many festivals and holidays are connected with the phases of the Moon, and a lunar calendar was used into modern times. A major lunar festival began on the 15th day (always a full moon) of the 8th month of the old calendar. By Xia times, we have already mentioned evidence for the existence of sidereal markers, thus suggesting a mixed calendrical system even at that early time. But the seasons demanded attention to the Sun's movements, hence, the need for accurate measurements, and thus, observatories such as the solar meridian tower near Luoyang (Wade-Giles: Loyang) (see §3.3). Equal double hours, 12 to the day, were used in ancient China.

The reconciliation of lunar and solar motions occupied the attention of Chinese as it did European astronomers. The Chinese name for the Metonic cycle was the chang, an interval of 235 lunar synodic months, which was approximately equal to 19 tropical years (see §4.2.1). In the west, the Callippic cycle consisted of four Metonic cycles; the corresponding cycle in China was called pu (76y Julian years). Other intervals were in use as well: A hui, an eclipse interval of very nearly 513 years, was equal to 27 chang. Three hui in turn made up a thung, ~1539 years, and 3 thung (~4617 years) was the shortest interval for reconciliation of these cycles and a 60-day sexagenary cycle. In addition, 20 pu = 1 chi (or sui) = (~1520y), 3 chi = 1 shou, and, according to one Han source,18 7 shou = 1 chi (~31,920y). After this interval, the same source says that all things will end and return to their "original state." This is equal to four Julian cycles of 7980 years each. The Julian cycle was invented, independently presumably, by Joseph Scaliger in the 16th century. The concept of a grand cycle of ages was widely held throughout the world. Liu Hsin (46 b.c.-a.d. 23) used an era base of 143,231 b.c. (Chang 1980, pp. 16-17). In the Han dynasty, it was supposed that the planetary cycles repeated every 138,240 years. When this was combined with the three-thung cycle of 4617 years, the result was a "world-cycle" of 23,639,040 years (Needham 1959, p. 408). Lunar and Planetary Observation

Needham (1959, p. 392) states that native Chinese astronomy never attempted an advanced analysis of the lunar motions, but the results of Chinese studies of the Moon are impressive nevertheless. Although Needham asserts that the synodic month has been determined to be 29d53 from oracle bones of the 14th century b.c., we think this determination (and the assigned date for the oracle bones allegedly containing the data) highly uncertain. However, by 237 a.d., Yang Wei provided the value 29d530598, and later determinations brought this to 29d530591 (compared with the modern value of 29d530588) by 463 a.d. The departure of the Moon from the ecliptic and the variation of the Moon's orbital speed was recognized by the astronomer Shih Shen [fl. ~371—340 b.c.]. The effect of the advance of the Moon's line of apsides is provided in the graphical "Nine Roads of the Moon," first mentioned by Liu Xiang [~11 b.c.]. Needham (1959, pp. 392-393) states that these "roads" were originally assigned the colors green, white, red, and black. Because the period of apsidal motion is 3232d575 ~ 8y85, they essentially demonstrate the annual change in the orientation of the elliptical orbit among the background stars.

The regulation of seasons involved the planets as well as the Sun, because of near-commensurabilities among the

18 The Chou Pei Suan Ching, "Arithmetical Classic of the Gnomon and the Circular Paths of Heaven" (Needham 1959, pp. 406-407;Ronan/ Needham 1981, p. 193).

Table 10.7.

Planetary associations.

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