Gan-Shi xingjing 甘石星經

Gan-Shi xingjing 甘石星經 "Master Gan's and Master Shi's star manual", also called Tongzhan daxiang lixing jing 通占大象曆星經 "Comprehensive classic of divination by the great starry constellations in the course of time", or Shishi xingjing 石氏星經 "Master Shi's star manual", or shortly Xingjing 星經 "Classic of the stars", is a book on astronomy and astrology whose core components were compiled during the Warring States period 戰國 (5th cent.-221 BCE). It is attributed to the astrologers Gan De 甘德 and Shi Kun 石申.

The bibliography Junzhai dushu zhi 郡齋讀書志 by the Song-period 宋 (960-1279) scholar Chao Gongwu 晁公武 (1105-1180) says that the book Gan-Shi xingjing was compiled by a Han-period 漢 (206 BCE-220 CE) author called Gan Gong Shi 甘公石 "Master or Duke Shi from Gan", which might be a clerical error. The imperial bibliography Jingji zhi 經籍志 in the official dynastic history Suishu 隋書 lists several books related to this text, namely Shishi xing bo jing zan 石氏星簿經贊 "Praise poems to the book of star registers by Master Shi" (which might be the original text), Xingjing 星經, and Ganshi si-qi fa 甘氏四七法 "Master Gan's four-seven methods".

Gan De hailed from the regional state of Qi 齊, or probably from Lu 魯 or the southern state of Chu 楚. According to traditional accounts he observed and fixed 118 stars (hengxing 恒星) and counted 511 stars in the whole sky. This information can be found in the treatise Tianwen lüe 天文略 in the Song-period encyclopaedia Tongzhi 通志. Gan De's book Tianwen xingzhan 天文星占 "Astronomical star prognostication", with a length of 8 juan, is long lost.

Shi Shen Kun or Shi Shenfu 石申夫 hailed from the state of Wei 魏 and lived around the same time as Gan De. He had fixed 138 starry constellations and counted 810 stars in the sky. It is said that he had already constated a different velocity of the moon on its course around the earth and that it deviated from the normal course of the ecliptic (huangdao 黃道). He furthermore was convinced that lunar and solar eclipses were the result of a mutual covering of the celestial bodies. His book Tianwen 天文 "Astronomy" (literally "Patterns of the sky"), with a length of 8 juan, is likewise lost. He also wrote the book Huntian tu 渾天圖, a map of the starry sky that has not survived. The Tianwen is listed in the bibliography Qilu 七錄 by the Liang-period 梁 (502-557) scholar Ruan Xiaoxu 阮孝緒 (479-536). The Tianwen was probably the basic writing from which all later texts developed that were attributed to Shi Shen and Gan De. From the Han period 漢 (206 BCE-220 CE) on it was called Shishi xingjing.

During the Three Empires period 三國 (220-280), the Grand Astrologer (taishi ling 太史令) of the empire of Wu 吳 (222-280), Chen Zhuo 陳卓, collected the statements by Shi Shen, Gan De and a third astrologer, Wu Xian 巫咸, and compiled a book including information about 283 constellations (xingguan 星官 "star offices or officials") with 1,464 stars.

The masters Shi and Gan had already calculated and noted down the distance of 120 stars from the ecliptic and the polestar, and so their exact position. They had thus created the earliest map of the starry sky. The Tang-period 唐 (618-907) book Tang Kaiyuan zhanjing 開元占經 records the 121 names and descriptions of the stars by Master Shi (6 are missing). Part of these had been calibrated during the Han period, but especially the data for the twenty-eight lunar mansions (ershiba she 二十八舍 or ershiba xiu 二十八宿, sic!) correspond to the time of Shi Shen. The text describes the movements of sun, moon, the five planets, the "three surroundings" sanyuan 三垣 (of the polestar: the constellations Ziwei 紫微, Taiwei 太微 and Tianshi 天市) and the twenty-eight lunar mansions, and their appearance, but also, how these might be used to gain astrological information. Each constellation was related to a certain office in the imperial administration. The polestar and his four "assistants" (sifu 四輔), for instance, reflected the relationship between the emperor and his chief ministers. The constellation Shangshu xing 尚書星 was related to the Imperial Secretariat (shangshusheng 尚書省), where memorials to the throne were processed around the clock. The constellation Yinyang xing 陰德星 was related to the equalized spread of wealth in the empire, and the constellation Wuguan xing 巫官星 with the health of the emperor.

The interpretation was effected in the following way: The constellation Gouchen xing 鈎陳星, for example, was related to the chief consort (zhengfei 正妃) of the emperor, the generals of the six armies of the heir apparent (tianzi liujun jiangjun 天子六軍將軍), and the Three Dukes (sangong 三公). If this constellation was darkened (an 暗), this was a sign of danger for the emperor. In other constellations, brightness was interpreted as military rebellion, a diminution in brightness as death, a change in the position towards the polestar as an attempt of usurpation, and so on.

The coordinates of individual stars (tianti 天體) of the twenty-eight lunar mansions are indicated by their distance, in degrees (judu 距度), from one reference star (juxing 距星) of the constellation. The vertical distance (qujidu 去極度) from the polestar (beiji 北極) is measured along a perpendicular line reaching from the polestar to the celestial equator (chidao 赤道), and its horizontal distance (ruxiudu 入宿度) from the last point, along the equator to the point where a perpendicular line from the reference star meets the equator. The Shishi xingjing has thus already developed a kind of coordinate system with a celestial equator. The celestial equator is divided into 365.25 degrees (and not, like in the West, in 360 degrees), corresponding to the length of the year. This is very uncomfortable for calculation, but fits better for the observation of the "movements" of the sun. Parts of degrees are expressed in the following way: tai 太 "great" (3/4 of a degree), ban 半 "half" (half a degree), shao 少 "small" (1/4 of a degree), qiang 強 "strong" (1/8 of a degree), ruo 弱 "weak" (1/8 degree less than the degree given).

The book also records the movements of the five planets Mercury, Venus, Mars, Jupiter and Saturn and their culminations (jiaoshi 交食). The brightness or "colours" of the five planets when crossing the lunar mansions was expressed in the following way: xi 喜 "joyful", nu 怒 "enraged", mang 芒 "awn", jiao 角 "corner". For the movements of the planetary revolutions the following terms were used: progressive movement (shun 順), retrogradation (ni 逆), stationary (liu 留) or hidden (fu 伏).

The Gan-Shi xingjing is the result of these scholarly efforts. The original was lost, but it is included in the Kaiyuan zhanjing (scrolls 65-70). Quotations can be found in the treatise Tianguan shu 天官書 that is part of the history Shiji 史記, written during the Former Han period 前漢 (206 BCE-8 CE). The astronomical treatise Tianwen zhi 天文志 in Sima Biao's 司馬彪 (240-306) Xuhanshu 續漢書, a history of the Later Han period 後漢 (25-220 CE), also quoted from Shi Shen's book, but with the greatest part of the Xuhanshu, these went lost.

The title Gan-Shi xingjing is first mentioned in the Song-period bibliography Junzhai dushu zhi, where it is listed with a length of 1 juan. The received version has a length of 2 juan. It is included in the Daoist Canon Daozang 道藏, where it has the lengthy name Tongzhan daxiang lixing jing.

Seen from the history of transmission there can be no doubt that the separately transmitted text of the Gan-Shi xingjing is a forgery compiled during the Tang period or later which can be seen in the fact that the Gan-Shi xingjing mentions place names from the Sui 隋 (581-618) and Tang periods and can therefore not have been written at an earlier point of time. The Qing-period 清 (1644-1911) scholar Qian Daxin 錢大昕 (1728-1804) speaks about the Gan-Shi xingjing in his book Yangxinlu 養新錄, where he likewise assumes that it is a forgery of later times. This version is included in the series Han-Wei congshu 漢魏叢書, Jindai mishu 津逮秘書 and Congshu jicheng 叢書集成.