Wuxingzhan 五星占

Wuxingzhan 五星占 "Divination by the Five Planets" is a text on astronomy and astrology compiled around 170 BCE and found in the Former-Han-period 前漢 (206 BCE-8 CE) tomb of Mawangdui 馬王堆 close to Changsha 長沙, Hunan.

The text, approximately 8,000 characters in length, is divided into nine chapters: Jupiter (Muxing 木星), Venus (Jinxing 金星), Mars (Huoxing 火星), Saturn (Tuxing 土星), Mercury (Shuixing 水星; also referred to as Xiaobai 小白, a name not found in other records), General Discussion on the Five Planets (Wuxing zonglun 五星總論), Jupiter's Motion (Muxing xingdu 木星行度), Saturn's Motion (Tuxing xingdu 土星行度), and Venus's Motion (Jinxing xingdu 金星行度).

It preserves portions of ancient Chinese astronomical writings by Gan De 甘德 and Shi Shen 石申 in their original form. Their books Tianwen xingzhan 天文星占 and Tianwen 天文, respectively, are lost, while the book Gan-Shi xingjing 甘石星經 is a later, thoroughly revised version from the Tang period 唐 (618-907).

Figure 1. Detail of the silk manuscript Wuxingzhan 五星占

From the Hunan Museum.

The Wuxingzhan records the positions of Jupiter, Saturn, and Venus over a 70-year period, from 246 to 177 BCE. The book details the dynamic movements of these three planets within a single synodic cycle. Venus receives the most detailed treatment, comprising nearly half of the content. It not only records Venus's synodic period but also acknowledges that five synodic periods (modern term huihe zhouqi 會合周期) of Venus correspond almost exactly to eight years. By utilising this relationship, the book constructs a 70-year table of Venus's motion. Furthermore, it notes the changes in the planet's brightness at superior conjunction (shanghe 上合) and inferior conjunction (xiahe 下合), illustrating an advanced understanding of planetary behaviour.

The text preserves records of Jupiter's sidereal period (hengxing zhouqi 恒星周期), continuing the astronomical values once calculated by Shi Shen and Gan De. It adheres to the tradition of assigning a 12-year cycle to Jupiter's movement. Furthermore, it refines the synodic period of Jupiter to 395.4375 days, marking an advancement beyond the values presented in the Shiji 史記 (ch. Tianguan shu 天官書) and Huainanzi 淮南子 (ch. Tianwen xun 天文訓) from the mid-Former Han period. The calendrical reckoning of Jupiter's movement in the Mawangdui manuscript also differs from these later records, which adhere to the traditions of Gan and Shi. The Hanshu 漢書 chapter Lüli zhi 律曆志, which combines musical measurements with calendrical calculations, is based on yet another system, the Taichu Calendar (Taichu li 太初曆). This implies that different astronomical traditions coexisted in early China, with the Mawangdui manuscript representing an alternative approach to planetary calculations and calendrical systems. However, the Mawangdui silk manuscript predates the earliest transmitted astronomical texts by 90 years, making it the earliest known astronomical text still in existence.

With regard to the motions of the five planets (wuxing xingdu 五星行度), the book differentiates between fast (kuai 快), slow (man 慢), retrograde (ni 逆), and stationary (liu 留) motions. The text demonstrates that astronomers of the era understood the fundamental relationship between time, speed, and distance (applying the essential equation speed × time = distance), linking planetary dynamics with positional calculations. This method established the foundation for later Chinese calendrical systems that integrated techniques for predicting planetary positions, known as bu wuxing 步五星, the systematic "pacing" (bu 步) or tracking of the five visible planets in Chinese astronomy.

The manuscript records Venus's synodic period as 584.4 days, which is 0.48 days longer than the modern measured value. Saturn's synodic period is recorded as 377 days, which is 1.09 days shorter than the modern value. Saturn's sidereal period is given as 30 years, which is 0.54 years longer than the modern measurement.

For fractional values, the manuscript standardises all denominators to 240 (instead of contemporary base-60 or decimal fractions). This decision, regardless of its original purpose, provides the clear benefits of simplified calculations and easy comparison of numerical values.

While the text contains significant astronomical observations, it also incorporates elements of superstition and philosophical concepts. From the Warring States period onward, with the development of Yin-Yang and Five Elements theory (yinyang wuxing shuo 陰陽五行說), the Five Planets became increasingly associated with the Five Agents (wuxing 五行) and their corresponding deities and cosmic influences. Each planet's movement was thought to signal auspicious or inauspicious events, and their interactions were interpreted as celestial omens. One notable event frequently mentioned in ancient texts is a "five-star gathering" (wuxing ju 五星聚) or "five-planets alignment" (wuxing zhulian 五星連珠), wherein all five planets appear in the same region of the sky. As this phenomenon is rare, it was often regarded by ancient astronomers as a symbol of great fortune and divine favour.

The text was first transcribed and published in the 1978 edition of the serial Zhongguo tianwenxue shi wenji 中國天文學史文集.