Butian ge 步天歌

Butian ge 步天歌 "Song of the wanderer through the sky" is a didactic poem about the starry sky and astronomical constellations. It is first listed in book catalogues from the Northern Song period 北宋 (960-1126). The astronomical chapter Tianwen lüe 天文略 in Zheng Qiao's 鄭樵 (1104-1162) statecraft encyclopaedia Tongzhi 通志 calls its author Danyuanzi 丹元子 "Master from the Cinnabar Origins" from the Sui period 隋 (581-618), and says that the long poem was commented on by the Tang-period 唐 (618-907) master Wang Ximing 王希明 on the basis of the astronomical chapters in the official dynastic histories Hanshu 漢書 (26 Tianwen zhi 天文志) and Jinshu 晉書 (11-13 Tianwen zhi). However, Zheng Qiao, in his bibliographical chapter Yiwen lüe 藝文略, holds that Wang Ximing was the author of the song Danyuanzi butian ge 丹元子步天歌.

The Butian ge pioneered the division of the night sky into three regions (sanyuan 三垣) and twenty-eight lunar mansions (ershiba xiu 二十八宿), totaling thirty-one celestial regions (tianqu 天區). Each region contains a varying number of star constellations and stars. This method of division is entirely different from the system used in the early Tang period, for instance, by Li Chunfeng 李淳風 (602-670) in the astronomical chapters of the Jinshu and Suishu 隋書 (19-21 Tianwen zhi), but it is largely similar to the methods used in astronomical texts from the Song period onwards. This serves as clear evidence that the Butian ge is not a work from the Sui period, but from about the tenth century.

Wang Ximing 王希明, also known as Tongxuanzi 通玄子 or Qingluo Shanren 青蘿山人, lived in the first half of the 8th century. He was recognised as an expert "magician" or diviner and was an editorial assistant (zhaodai 待詔) in the Hanlin Academy 翰林院. He also wrote the divinatory text Taiyi jingjingshi jing 太乙金鏡式經 and the song Yusi ge 聿斯歌 on soothsaying by the stars.

It is said that Zhang Heng 張衡 (78-139) composed a "Rhapsody on celestial phenomena" (Tianxiang fu 天象賦) during the Later Han period 後漢 (25-220 CE), but this is likely unreliable. A more credible work is the "Rhapsody on observing celestial phenomena" (Guanxiang fu 觀象賦), written around 438 CE by Zhang Yuan 張淵, who was Grand Astrologer (taishi ling 太史令) at the court of the Northern Wei dynasty 北魏 (386-534). Another early testimony of astronomy is the "Rhapsody on the grand celestial phenomena" (Tianwen daxiang fu 天文大象賦), composed by Li Bo 李播 during the Sui period. Additionally, the Dunhuang Caves have revealed the "Poem of the mysterious celestial patterns" (Xuanxiang shi 玄象詩), dating back to the early Tang period. However, all these works, due to their excessively ornate language and greater artistic rather than practical value, ultimately failed to gain widespread use. Only the Butian ge, with its concise and clear wording, melodious rhythm, and ease of memorization, quickly spread and became popular. The verses of the Butian ge are concise, straightforward, and well-organized. Zheng Qiao praised it for being "an image in every verse, a symbol in every word" (ju zhong you tu, yan xia jian xiang 句中有圖，言下見象).

The lyrics of the Butian ge are written in seven-character verses (totalling 373 verses), with rhyme. The text introduces the names and numbers of stars, and locations of various star constellations. Due to this structured yet concise approach, the text became a standard reference for the Directorate of Astronomy (qintianjian 欽天監) and astrologers from the Song dynasty onward, serving as a key source for astronomical studies and celestial divination.

Each line of the song vividly depicts the celestial formations, allowing readers to visualize the stars as they recite. By chanting the verses while gazing at the sky, learners can accurately match the number of stars in the song to those observed, making it an essential mnemonic for beginners in star recognition and celestial observation. When reciting the poem, if one simultaneously steps in the direction indicated by the verses, it mimics moving from one star to another in the sky. This method makes it easier for learners to visualize, memorize, and understand the arrangement of stars, providing an intuitive way to grasp ancient Chinese astronomy.

The text of the Butian ge is included in the Lingtai biyuan 靈臺秘苑 (ch. 1).

In ancient China, stellar observations had taken shape by the Spring and Autumn 春秋 (770-5th cent. BCE) and Warring States 戰國 (5th cent.-221 BCE) periods and became largely standardized by the Han period 漢 (206 BCE-220 CE). During the Three Empires period 三國 (220~280 CE), Chen Zhuo 陳卓, the Grand Astrologer (taishi ling 太史令) of the state of Wu, compiled around 270 CE a new comprehensive star map based on the records of three earlier astronomers - Gan De, Shi Shen, and Wu Xian. His star map documented 283 constellations with a total of 1,464 stars. Chen Zhuo used three colors (yellow, red, and black) to distinguish the observations recorded by the "star officials" (xingguan 星官) Gan De 甘德 (circles), Shi Kun 石申 (black dots), and "Magician" Wu Xian 巫咸 (yellow dots; see Gan-Shi xingjing 甘石星經). This map is considered a foundational representation of China's ancient Canopy Heaven model (gaitian 蓋天), but unfortunately, it was soon lost. Today, its general structure can only be inferred from the silk-drawn star maps (Types A and B) discovered in Dunhuang. By the early Tang period, the stars were organized into 31 major regions, forming the well-known Three Enclosures and Twenty-Eight Mansions. As a result, after its creation, the Butian ge spread widely among the common people. However, at the time, rulers exercised strict control over astronomical and astrological works, particularly those related to star divination. Before long, the song was regarded as a precious secret and was archived in the Secret Repository of the Numinous Terrace (Lingtai Biyuan 靈臺秘苑), which meant that ordinary people were no longer able to access it. Because it was kept secret by astrologers, the Butian ge also became known as Tianwen guiliao qiao 天文鬼料竅 "Secrets of ghostly materials of astronomy", or Guiliaoqiao 鬼料竅 for brief.