Tianwen xun 天文訓

Tianwen xun 天文訓 is an astronomical chapter in the Daoist book Huainanzi 淮南子 from the Former Han period 前漢 (206 BCE-8 CE). It was compiled by retainers at the court of Liu An 劉安 (179-122), Prince of Huainan, and – apart from Huang-Lao thought that prevailed at the time – also integrated aspects of Confucianism, legalism, and the school of Yin-Yang thought 陰陽. The latter, again, was related to the field of astrology and astronomy. The book was finished in 139 BCE.

The content of Tianwen xun is extremely rich. The book describes the origins of the universe, theories of cosmic evolution, the divisions of the sky, the distribution of the 28 Lunar Mansions (ershiba xiu 二十八宿), the relationship between the Five Planets (wuxing 五星) and the Five Agents (wuxing 五行), methods for measuring wind and shadow (hou feng ce ying 候風測影), astronomical phenomena and seasonal markers, the twelve-tone musical scale (shi'er yinlü 十二音律), the Yin-Yang and Five Elements theory, taboos and regulations, the lunar calendar system, prohibitions related to the twelve-year Jupiter cycle, and more. It incorporates astronomical theories from the early Han dynasty and preserves a wealth of knowledge from the pre-Qin period (before 221 BCE). As such, it serves as a comprehensive synthesis of astronomical knowledge and thought of its time.

The Tianwen xun first describes the origin and evolution of celestial bodies according to cosmological theories. Before the heavens and earth, the primordial state took shape in an undifferentiated, chaotic void (dazhao 大昭). Then, the Dao 道 emerged in the state of emptiness and vastness (xukuo 虛廓), followed by the formation of space and time (yu 宇 and zhou 宙). In this space, cosmic matter, energy, or ether (qi 氣) was embedded. Pure and light (qing yang 清陽) ether ascended to form the heavens, while heavy and turbid (zhong zhuo 重濁) ether sedimented and condensed to form the Earth. At the same time, the refined essences (xi jing 襲精) of Heaven and Earth generated the dual forces of Yin and Yang. The concentrated essence of Yin and Yang gave rise to the four seasons (sishi 四時), and the dispersed essence of the four seasons produced the ten thousand things (wanwu 萬物). Yang ether generated fire, and the refined essence of fire formed the Sun. Yin ether formed water, and the refined essence of water formed the Moon. The excess essence of the Sun and Moon manifested as the stars. This cosmological model reflects the ancient Chinese perspective on the interconnectedness of natural forces and the formation of the universe.

This detailed description of cosmogony makes the Tianwen xun the first work of its time to outline this cosmological process in a more systematic way than the early Daoist writings or the famous Tianwen 天問, part of the Chuci 楚辭 collection. Later, the Huainanzi model was modified by Zhang Heng 張衡 (78-139) in his work Lingxian 靈憲, further shaping the development of Chinese cosmology.

The Astronomy Chapter continues by describing the four seasons, Sun and Moon, stars, rainbows, halos, and comets. It also elaborates on the Nine Fields (jiuye 九野) of the sky and its 9,999 junctures (yu 隅), stating that the heavens were 150,000 li "miles" (1 li = c. 0.5 km) above the Earth. It details the Five Planets, the Eight Winds (bafeng 八風), the Twenty-Eight Lunar Mansions, the Five Offices and Six Departments (wuguan liufu 五官六府), the Grand Enclosure (taiwei 太微) as the hall of the Grand One (taiyi 太一; a star-deity), the Purple Enclosure (zigong 紫宮) as his palace, the Chariot Frame (xuanyuan 軒轅) as the residence of his imperial consort, his Xian Pond 咸池, the Heavenly Slope (tian'a 天阿) as a gate tower housing the assembled spirits, and the Four Guardians (sigong 四宮) dispensing rewards and punishments. The authors expound on the motion of the Sun and Moon, the completion of annual cycles, and the relationships between the "two diametrical cords" (ersheng 二繩: between the days ziwu 子午 and maoyou 卯酉), "four hooks" (sigou 四鈎: chouyin 丑寅, chensi 辰巳, weishen 未申, wuhai 戌亥), the four cords (siwei 四維), the two solstices (erzhi 二至), the ether of Yin and Yang, the seasonal cycle of all things, the Agents Water and Fire in relation to Yin and Yang, seasonal transitions and the interconnected changes in all living things, the Seven Habitations (qishe 七舍: the room, hall, court, gate, lane, road, and field), the direction of the Dipper handle (dou 斗) in winter months and its correlation with the seasons and musical tones.

The Tianwen xun further explains the relationship between the Moon's movement within the year and the greater cosmic cycles, the combinations of Yin and Yang resulting in the Five Notes and Six Pitch-Pipes (wuyin liulü 五音六律; see Lüli zhi), the use of intercalary months (runzhou 閏周), solar omens and phenology (rizhan 日占, wuhou 物候), the position of the "Grand One" in winter and spring, the association of the Five Agents with annual affairs and their influence through the Heavenly Stems and Earthly Branches, taboos and prohibitions regarding all things and the movement of ether through the twelve hours of the day (xing shi'er shi zhi qi 行十二時之氣). This detailed work not only organises astronomical knowledge systematically but also intertwines cosmology, meteorology, music, divination, and seasonal changes into a comprehensive worldview.

In the following section, the treatise discusses Yin-Yang and its relationship with the Sun's orbit and timekeeping, the correlation between musical tones and the twelve months, the numerical relationships between musical scales, measurements, and units of length, the connection between the Moon (Taiyin 太陰), the Jupiter (taisui 太歲) cycle, the "Four Binding Cords", and the Twenty-Eight Lunar Mansions, Jupiter's cycle in calendrical reckoning (suixing jinian 歲星紀年), lunar omens and divination (taiyin zhanhou 太陰占候), the Twelve Monthly Phases (shi'er yue jian 十二月建), the division of the Twenty-Eight Mansions and their corresponding terrestrial locations, the generative cycle of the Five Agents (wuxing xiang sheng 五行相生), the deities associated with the Big Dipper (beidou zhi shen 北斗之神), astrological predictions based on Jupiter's position (suixing zhan 歲星占), methods for determining cardinal directions and the movement of celestial bodies, the measurement of solstices and equinoxes, techniques for calculating the dimensions of the four cardinal directions and methods for determining the distance to the celestial poles.

The Tianwen xun encompasses nearly all branches of knowledge related to astronomy, celestial phenomena, music theory, the Five Agents, and the Heavenly Stems and Earthly Branches system. While its structure is not entirely systematic and it contains elements of Yin-Yang mysticism and astrological divination, it still stands as the first comprehensive and systematic treatise of astronomical theories and celestial knowledge from the pre-Qin to the early Han period in ancient China. The Tianwen xun presents the earliest systematic accounts of the motion of the Five Planets, the Heavenly Stems and Earthly Branches, the stations of the Jupiter cycle, the solar terms, the link between musical theory and astronomy, numerical data on the Moon's daily average motion (recorded as 13°7') and the gnomon of ten chi height (see weights and measures).

Although the chapter was written earlier than the Shiji, with the chapter Tianguan shu 天官書, the sequence of the Twenty-Eight Lunar Mansions recorded in the Tianwen xun is more accurate than that in the Tianguan shu. Later astronomical and calendrical treatises, therefore, adopted the sequence established in Tianwen xun.

Apart from comprehensive commentaries on the Huainanzi, like Xu Shen's 許慎 (c. 58-c. 147) Huainanzi zhu 淮南子注, Gao You's 高誘 (c. 200 CE) Huainan honglie zhu 淮南鴻烈注, Chen Changji's 陳昌齊 (1743-1820) Huainanzi zhengwu 淮南子正誤, Liu Taigong's 劉臺拱 (1751-1805) Huainanzi bujiao 淮南子補校, Yu Yue's 俞樾 (1821-1907) Huainan neipian pingyi 淮南內篇平議 and Hu Huaichen's 胡懷琛 (1886-1938) Huainanzi jijie buzheng 淮南子集解補正, there is a special study on the astronomy chapter, namely Qian Tang's 錢塘 (1735-1790) Huainanzi tianwen xun buzhu 淮南子天文訓補注.