Imperial Stars9 min read

Jonathan Chatwin reviews Heavenly Numbers by Christopher Cullen

High on a solitary outcrop of crenellated city wall in Beijing – an anomaly among the towering glass and concrete – sits China’s Imperial Observatory: a collection of the astronomical instruments with which the officials of the Qing dynasty tracked the movement of the heavenly bodies.

It is a relic of an age that can often seem confoundingly distant in modern China. The small stretch of city wall is one of the only sections of that fortification remaining, the rest having been demolished in the two decades after the Communist Party came to power in 1949. That absence finds an ironic echo in the name of the adjacent subway stop and traffic intersection: Jianguomen, the “Gate of National Construction.” This was one of the gates punched through the old city wall by the Japanese, during their occupation of the city in the late 1930s. It met its end, along with much along this axis of the city, in the 1960s as the government began constructing a subway system. The observatory would have been destroyed as well, were it not for the intervention of Premier Zhou Enlai, who insisted that it be preserved, as he did with a number of significant historical sites during the Cultural Revolution.

The noise of the second ring road – the construction of which brought down much of the rest of the city wall – is a persistent percussive interruption to those who might seek to ponder celestial matters amongst the instruments of the observatory. Mostly designed in the late seventeenth century by the Jesuit missionary Ferdinand Verbiest who, like earlier emissaries from the Catholic church, had proved his value to the emperor through the accuracy of his astronomical predictions, these too are symbols of China’s long history, testifying to the importance placed by successive imperial dynasties on recording and understanding the heavens.

In Heavenly Numbers: Astronomy and Authority in Early Imperial China (Oxford, 2017), the Cambridge historian of science Christopher Cullen has returned to early written records to trace the origins of these Chinese systems of measuring and recording the movement of the celestial bodies, and to examine how this influenced the development of the calendar. Heavenly Numbers covers the development of astronomy in the Early Imperial period, from the late third century BCE to the early third century CE, the period of the Qin and Han dynasties: an era in which the astronomical and calendrical systems were established that would, in some form or another, endure officially until China’s imperial age ended with the fall of the Qing dynasty in 1911.

For many of us today, the systems of dividing and ordering time used in the Gregorian calendar by the majority of nations will rarely give pause for thought: a day is a day; January is January; and a year is 365 days (except when it isn’t). Yet this study of the ancient Chinese approach to systematising the passage of time offers a correction to any intellectual complacency, confronting us with a method of recording the cycles of the moon and the sun which functions quite differently from those which developed in much of the rest of the world.

The Early Imperial way of measuring the passage of time was lunisolar. Cycles of the moon offer an obvious division of time, of course. You can trace the days from full or new moon to the next one, without any equipment – all you need to do is watch the sky and count. If you begin your count of these lunations in spring, you will find that, in roughly twelve moons time, you will find yourself back in the same season – which might lead you to think that this matches a full cycle of the seasons. But if you repeat this approach and count another twelve moons, you will find yourself out of sync with the seasons, and the weather a little more wintery than you were anticipating. As a cycle of twelve moons is about 11 days shorter than the time it takes for the sun to return to the same position relative to the earth, lunisolar calendars periodically throw in a ‘leap month’ to catch up with the sun. If you keep records for a couple of decades, the pattern becomes clear: every nineteen years, you are required to add seven extra moons to keep in step with the seasons.

The instruments at Beijing’s Imperial Observatory museum designed by Verbiest include a Celestial Globe, an Ecliptic Armilla, an Equatorial Armilla, a Theodolite, a Quadrant, and a Sextant.

Many ancient calendars, including the Hebrew and Tibetan systems, were lunisolar. In China, records suggest that the lunisolar calendar goes back to the second millennium BCE. Dividing time up into months and years was supported by two additional elements. The first was reign titles – the names given to different phases of an emperor’s reign. In the era of the Han dynasty, these would change if something particularly auspicious or significant happened; when in 116 BCE the Emperor Wu – an illustrious ruler of the Han dynasty who vastly expanded the territorial borders of the Middle Kingdom – dug up an ancient bronze tripod with a mysterious inscription, that year became known as first year of the ‘Epochal Tripod’ era. The second part was a naming system for days which used paired characters, which meant that days repeated on a sixty day cycle; it is from these sexagenary names, later applied to years, that we get the name of the Xinhai revolution which overthrew the Qing, after the ancient nominal for the year it occured in 1911. Combining all these elements, one exemplar day in the Han dynasty when a solar eclipse occurred was recorded as “Epochal Tripod fifth year, fourth month, dingchou (fourteenth day of the sixty day cycle),” corresponding to our June 18, 112 BCE, when an eclipse was indeed visible at the Han capital, Chang’an.

The calendars and records which allow us to know of such events were kept carefully by the officials of the emperor, who took it as a primary responsibility of theirs to keep track of the movement of the heavens. The emperor was, after all, the physical connection between the human order and the heavenly order. As such, it was expected that his court would tell his subjects in advance what the heavens would be doing, by giving them a calendar. The emperor needed to pay close attention to its accuracy; if unexpected celestial events transpired, this could be a warning that the emperor was mismanaging the country, or a portent of disaster, and that he might be about to lose the ‘Mandate of Heaven’: the divine right to rule.  

Effective management of the calendar likewise promised divine rewards. In the last years of the second century BCE, the Emperor Wu reformed the calendrical system to match that of the legendary Yellow Emperor, performing rites in the hope that he, like his hero, would attain eternal life. Having undertaken the appropriate ceremonies on the appropriate dates, he sent messengers to China’s eastern coast to watch for the appearance of immortals from Penglai, the mythical mountain island where they were supposed to live. None appeared. Later he went himself to gaze across the eastern seas, returning home disappointed – though not deterred. In 104 BCE, his new astronomical system was inaugurated, and, as Christopher Cullen writes, his belief in the attainment of immortality remained strong, despite the tangible lack of earthly or heavenly evidence.

Two millennia later, and the calendar still used by the imperial Chinese court was principally the same as that inaugurated by Wu. The instruments of the Observatory in Beijing – a mere provincial town when the Han dynasty ruled – were testament both to the central importance of the movement of the heavenly spheres in the Ming and Qing eras. The site of the Observatory was chosen, so Osvald Sirén records, due to the belief that the sun was at its most supreme in the south-east of the city. It dates back to 1442, more than a century before the invention of the telescope, though an earlier observatory existed on a site nearby from 1279. Instruments from the earlier dynasty had previously stood on the same platform; some are now in the garden below. In the autumn of 1900, Sarah Conger, wife of the chief American diplomat in Beijing, visited the Imperial Observatory and was struck by the manner in which they connected China’s past and present: “These fine old instruments,” she wrote in a letter to her sister, “standing above and below, show no wear of time, although centuries have passed over them. They are like China herself; and if let alone they will stand upon their dragon thrones for centuries to come.”

A few months later, the platform would be empty: the instruments stripped from their bases by the German and French troops of the Eight Nation Alliance who had arrived in Beijing to save the foreign population of the city from the siege of the Boxers. Those taken by the French would be returned the following year, but the other plinths would sit empty for some time. The five taken by German forces to be displayed in Potsdam would not be sent back to China until 1921, by which time the Qing empire was a decade fallen. So too was the lunisolar calendar, at least nominally. In 1912, the Gregorian calendar was adopted by the fledgling Republic of China under Sun Yatsen as China’s official calendar – a change which was largely ignored by a population attached by both familiarity and sentiment to the old system.

Today, the bronze instruments retain the same air of permanence that Sarah Conger noticed, despite the radical transformation of the city around them. The continuing influence of the moon year is testified to by the importance of almanacs for deciding propitious days for a marriage or the opening of a business, in the central significance and observance of annual festivals, and in the renewed popular affection for the 24 jie qi or solar terms which break the years up with seasonal markers. These periods of roughly fifteen days capture the subtle seasonal shifts which, ringing as clearly as a bell for those who lived on the land, broke up the rural year. They label the meteorological conditions with precision and brevity: Clear Brightness (qing ming), for example, or Frost’s Descent (shuang jiang).

These ways of marking the changes between light and darkness, between winter and summer, between the old and the new year, sustain, it seems, not through any artificial means, but because over generations, they layer incrementally into an accretion of collective memory which is hard to simply sand-blast away. It is also the case, of course, that in the times of greatest uncertainty and reform, such traditions are consolations to be returned to, reassuring one that even in modern China, though much is lost, much also abides.

Christopher Cullen, Heavenly Numbers: Astronomy and Authority in Early Imperial China (OUP, November 2017).
The author wishes to thank Christopher Cullen for his time in answering questions and elucidating the many complexities of the Chinese calendrical system. All photos by the author.