Lunar calendar showcases splendid Chinese civilization
The Dunhuang Star Chart, one of the first known graphical representations of stars from ancient Chinese astronomy, at the British Library in London, UK Photo: Jiang Hong/CSST
The Calculation and Promulgation of the Chinese Calendar, which came into effect on Sep. 1, 2017, for the first time identifies the lunar calendar’s arrangement rules, calculation model, accuracy, and representation methods, providing a scientific standard basis for the calculation of the lunar calendar. The issue of this national standard also shows the long history of the ganzhi chronology method [also known as the sexagenary cycle or the stems-and-branches cycle], which embodies not only the development of the ancient Chinese calendar and astronomy, but also their distinct mathematical wisdom.
Celestial phenomena and calendar
“Identifying time by observing celestial phenomena” promoted the birth of the 24 solar terms. According to Feng Shi, a member of the Chinese Academy of Social Sciences (CASS) and a research fellow with the CASS Institute of Archaeology, there are detailed or concise descriptions of constellations and celestial phenomena in ancient classics, such as Book of Changes, Book of Documents, Classic of Poetry, Erya [an ancient Chinese lexicon], and Huainanzi. Among them, Huainanzi, dating back to more than 2,000 years ago, gave the most complete statement, calculation, and record of the 24 solar terms for the first time, proposing that each solar term is associated with 28 mansions [part of the Chinese constellations system], the operation of the Big Dipper, the length of the shadow measured by tugui [a type of sundial], and the phenology of different regions.
Seasons and solar terms are essentially a time system. “Identifying time by observing celestial phenomena” in ancient Chinese classics has been constantly confirmed by archaeological discoveries. In 2003, a large circular structure of rammed earth surrounded by 13 columns was discovered at the Taosi Site in Shanxi Province. There are 12 observation slots on the Taosi observatory through which the calendar law of 20 seasons in a tropical year can be observed. Observing the sunrise orientation on the Taosi observatory determined specific seasons which helped to arrange agricultural production. This discovery, and the excavation of guibiao [an ancient Chinese gnomon], are of great significance to astronomical history in China and even in the world, confirming the credibility of pertinent records in the “Yaodian” chapter of Book of Documents, and tracing the background knowledge of astronomy in China back to 4,000 years ago.
Starting their research from “identifying time by observing celestial phenomena” in the Xia (c. 21st–16th century BCE), Shang (c. 16th–11th century BCE), and Zhou (c. 11th–221 BCE) dynasties to the birth and use of the lunar calendar around the Warring States (475–221 BCE), the Qin (221–207 BCE), and Han (206 BCE–220) eras, scholars have further explored the tradition of planetary movement theory, exchanges between civilizations, and cultural integration.
Ancient Chinese people considered heaven dominant and earth subordinate. The ancients summarized the law of nature into ten attributes or symbols, and associated them with solar terms, gradually forming the tiangan [heavenly stems] system. Accordingly, in order to facilitate the observation and recording of the movement of the sun, moon, and “five planets” [Venus, Jupiter, Mercury, Mars, Saturn], the ancients chose 28 constellations near the equator as the reference index system for positioning. They divided the 28 mansions in the sky into 12 zones, and converted them into 12 partitions of plane scales on the dial, which was the earliest dizhi [earthly branches].
The heavenly stems and earthly branches became the daily descriptions of ancient people’s social life, which then became their codes to decipher the universe, space and time, culture, and life. The ten heavenly stems and 12 earthly branches matched one by one, forming 60 basic units which cooperated with each other in sequence and repeated in a cycle, forming the ganzhi chronology. The arrangement and combination of “heavenly creation” and “earthly design” reflects the plain view of nature and cycle of history.
Modern interpretation
In 1965, Xia Nai, one of the founders of modern Chinese archaeology and the main director and organizer of the PRC’s archaeological work, published his research on the tomb mural’s celestial painting of the Western Han Dynasty in Luoyang, Henan Province, which was the first academic work on the systematic observation of stars in ancient China based on archaeological data. Ten years later, starting from the stellar map of Liao Tomb in Xuanhua, Hebei Province, Xia discussed the signs of the zodiac as well as when and where the 28 mansions originated, which became the representative work of astronomical archaeology in China.
Zhang Wenyu, a professor with Guizhou University, acknowledged that Zhang Ruzhou made an unprecedented achievement in the 1960s by comprehensively interpreting the main development line of the ancient Chinese astronomical calendar. For more than two millennia, no one could figure out “Lishu Jiazi Pian,” a text on the ancient Chinese astronomical calendar in the “Calendar” chapter of Records of the Grand Historian by Sima Qian. With his solid ancient Chinese skills, precise textual research methods, and modern astronomical calendric knowledge, however, Zhang Ruzhou concluded that the segment written by Sima Qian was in fact China’s first calendar—Si Fei Li. He inferred that the year that started the implementation of Si Fei Li was 427 BCE in the early Warring States Period.
From the perspective of modern astronomy, the study of the ancient Chinese planetary motion theory began in the 1950s. After more than half a century, history of science has made rich achievements in the field. However, some difficult problems remain unresolved, mostly concentrating on a series of correction algorithms related to the aforementioned five planets’ equation of center, said Tang Quan, deputy director of the Institute for Advanced Study of Science History at Northwest University.
In 2008, Qu Anjing, director of the Institute for Advanced Study of Science History at Northwest University, completed the book Mathematical Astronomy in China, which elaborated on the algorithm evolution and theoretical system of solar motion, lunar motion, solar and lunar eclipses, and planetary motions in ancient Chinese mathematical astronomy. The book helps solve certain remaining problems regarding the traditional solar eclipse theory, builds an astronomical model of the traditional outer planet algorithm, and accordingly outlines the development of the traditional planetary motion theory.
Ancient China had frequent astronomical exchanges with other civilizations. The input of Indian astronomy during the Han and Tang (618–907) dynasties, Arab astronomy during the Yuan (1279–1368) and Ming (1368–1644) dynasties, Western classical astronomy and modern astronomy during the Ming and Qing (1644–1911) dynasties, all exerted a profound influence on the development of Chinese astronomy. In Tang Quan’s view, comparing the astronomical and mathematical similarities and differences between ancient China and other civilizations helps clarify understanding of the content, thoughts, methods, and achievements in mathematical astronomy of different civilizations. What’s more, such an endeavor has academic and practical value to locate the origin of modern science and establish the status of Chinese traditional numerical algorithms.
Edited by YANG LANLAN