Heaven Within Reach: Ascending the Ancient Observatory
Take Beijing’s subway, navigate the transfers, and arrive at Jianguomen Station. The moment you emerge from Exit C, you’ll spot a tall platform right next door.
The poet Li Bai loved his wine; even without drinking companions, he would “raise a cup to invite the moon, and with my shadow we become three.” At the end of his series “Drinking Alone Under the Moon,” he says, “Let me drink fine wine, and in moonlight climb a high platform.” Though the platform before me has indeed hosted many moonlit climbers, Li Bai was not among them. He lived in the Tang Dynasty, while this platform was built in the seventh year of the Zhengtong reign of Ming Emperor Yingzong (Zhu Qizhen)—680 years after Li Bai’s death.
Why did Li Bai climb high platforms? Su Shi of the Song Dynasty put it: “Blue stretches to the sky, among evening clouds. A high platform on the city wall—truly a place of transcendence.” In other words, Li Bai climbed for transcendence, to throw drunken punches and compose intoxicated poems. The others who came up here weren’t looking for wine but for another equally romantic pursuit: stargazing, “to watch meteor showers fall upon this earth.”
Before this Ming Dynasty platform, people in the Yuan Dynasty had already tamped down an earthen mound here to climb at night and observe the stars. Among them was Guo Shoujing, a bona fide astronomer. Over a thousand years before him, during the Eastern Han, Zhang Heng was already studying the heavens and geography. Before Zhang Heng, star reading was mostly the work of diviners. By the Sixteen Kingdoms period after the Eastern Han, star observation had become a profession—called astrologers. Last time at the Zhangbi Ancient Fortress in Shanxi from that era, I saw an astrologer figure perched under the eaves.
You see, that astrologer had no high platform to climb, so he had to lean a ladder against the outer wall of his house to gaze at the stars. This astrologer at Zhangbi was no longer a diviner; he didn’t predict personal fate or national destiny. His job was to clearly map the positions of the stars and then guide the village’s architectural layout.
By the Zhengtong years of the Ming Dynasty, Emperor Yingzong ordered the construction of the very platform we see today for the star experts. He wanted them to climb up and read fates and national fortunes—his own, naturally—and maybe do a bit of scientific research on the side. By then society had advanced; divination had become marginal, unfit for formal halls. Yingzong told the scholars to give the platform a scholarly official name. Before this, in the Yuan Dynasty, the mound Guo Shoujing climbed was called “Si Tian Tai”—the Platform of Heavenly Governance. Ming astronomers felt embarrassed by that name: how could mortals govern heaven? Even governing a car would be impressive enough. They believed heaven could not be governed, only observed, so they named it “Guanxiang Tai”—Observatory, a platform for observing celestial phenomena. The stone tablet inscribed with “Guanxiang Tai” still sits above the arch of the main gate; the red paint has faded with age.
The earliest formal sky observer in China was perhaps King Wen of Zhou, Ji Chang. In the “Book of Changes” he compiled, it says: “The signs of heaven reveal good and ill fortune; the sage models them.” This observatory in Beijing remained in use until the Purple Mountain Observatory was built in Nanjing in 1927, and in 1982 it was designated among the second batch of National Key Cultural Relics Protection Units.
The day I came to climb the platform, the sky was high, clouds wisps, visitors few, the terrace empty. No elderly gatekeepers at the entrances, and no building with a “Ticket Office” sign. The climbing gate was wide open; they said it had been like that since nine that morning—free admission.
Just as I stepped to the gate to ascend, I saw a hefty man sprawled on the steps, seemingly digging for something.
Though in broad daylight it was unlikely someone was literally undermining the wall, I still asked if he was a real-life tomb raider influencer. He said no, he was setting up to shoot time-lapse of rushing clouds. He complained that midway through filming, because he hadn’t guarded his gear like this, an old grandpa had come over and pressed a button on his device, ruining everything before and all the clouds had rolled by in vain. You know, some old grandpas truly have compulsive tendencies—they just can’t resist pressing buttons when they see them. That’s why missile unit soldiers are all young; imagine if some random old veteran casually pressed a random missile launch button, and the missile casually flew off somewhere, causing trouble for whatever US troops happened to be there.
Once I climbed the platform, there was no old grandpa, only a locked gatehouse.
Scattered around were seven or eight observation instruments.
In 1900, when the Eight-Nation Alliance invaded Beijing, these instruments were looted by French and German troops. The French hid a few in their Beijing embassy, returning them two years later. The Germans shipped the rest back home and displayed them in the New Palace behind Sanssouci in Potsdam; after Germany’s defeat in WWI, they were returned to China in 1921.
Look at the instruments on the platform. This one is called the “Jiheng Fuchen Yi” (the Armillary Sphere for Observing the Cosmos).
Admire its exquisite cast bronze details.
Also known as the Equatorial Armillary, the Jiheng Fuchen Yi was ordered cast in the 19th year of the Qianlong reign of the Qing Dynasty (1754). “Jiheng” comes from the “Book of Documents”: “With the armillary sphere and jade sighting tube, he regulated the seven heavenly bodies.” This instrument is slightly more complex than a standard equatorial armillary, with extra components. It was mainly used to measure the positions (right ascension and declination) of celestial bodies and solar time. In ancient times without atomic clocks, precise timekeeping relied on astronomical observation. Actually, even today time is based on astronomical observation; atomic clocks must be calibrated against astronomical time.
This one is the Ecliptic Armillary.
In the 12th year of Kangxi (1673), the emperor ordered the Belgian missionary Ferdinand Verbiest to build it, for measuring the ecliptic longitude and latitude of celestial bodies.
The next one, the Celestial Globe, was also built by Verbiest in the same batch.
It was used to demonstrate the positions of celestial bodies on the ecliptic and equator, as well as their apparent positions from the ground. Verbiest built several instruments at that time; the following Sextant is another.
The Sextant is used to measure the angular distance between two stars. Even if its intricacies are lost on us, we often see pictures of sailors at sea holding a sextant. In ancient navigation, beside the compass for direction, astronomical observation was essential for positioning.
Below is the Altazimuth.
Also built by Verbiest, it measures the azimuth angle of celestial bodies. He made six instruments in total, including this Quadrant below.
The Quadrant measures the altitude angle of celestial bodies.
Next is the Horizon Circle.
This Horizon Circle was also built during Kangxi’s reign, in the 54th year (1715). Notice it has no cast bronze coiling dragons; instead, it shows Western styling. It was not by Verbiest but by a German missionary named Kilian Stumpf. The Horizon Circle integrates the functions of both the Quadrant and the Altazimuth.
Most of the observation instruments on the platform were made by foreigners; so where are the domestic ones? I went down with this question and immediately saw ancient Chinese observation instruments in the courtyard. Check this out.
The Linglong Yi (Exquisite Sphere). This was built by students of Guo Shoujing following their teacher’s blueprints during the Yuan Dynasty. The metal sphere is essentially a thin shell with many tiny holes; you crawl inside and look around, seeing a sky full of stars. Because the holes were drilled according to a system, the starry sky appears very realistic. Across from Beijing Zoo there’s a planetarium with a projection hall where modern astronomers cast stars onto the dome—even more realistic than inside this Exquisite Sphere.
In the courtyard there’s also an Armillary Sphere.
China’s earliest armillary sphere was created by the Western Han astronomer Luoxia Hong during Emperor Wu’s reign—also the world’s first. It could measure the equatorial coordinates of celestial bodies. Since its invention, later scholars made many improvements. This one here is from the Ming Dynasty, with added functions, and it can also measure ecliptic and horizontal coordinates. Sixty years after Luoxia Hong’s armillary sphere, a similar instrument appeared in Greece.
There’s also an Abridged Armilla in the courtyard.
It is, as the name suggests, a simplified armillary sphere, designed by Guo Shoujing in the Yuan Dynasty. Three hundred years after Guo’s simplification, a Western version of a simplified Greek armillary sphere also emerged, built by a Dane.
This one I recognized immediately—a shadow measurer.
This is called a Guibiao (gnomon). The standing copper pillar is the “gui,” and the horizontal copper plate is the “biao.” At exactly noon, you read the length of the shadow cast by the gui on the biao’s scale, and you’ll know which season it is.
While the Guibiao tells the season, there’s another instrument for telling time: the “sundial.” In Chinese, “gui” and “gǔi” (sundial) sound similar.
If a sundial measures time by day, surely there’s a moondial for the night? Believe it or not, there is, though not here. Pass through this moon gate to see the moondial.
Here it is.
There’s even a stardial serving as the moondial’s sidekick because moondial timing isn’t very precise, so it needs a deputy to assist. The word “stardial” (star clock) appeared in China as early as the Southern and Northern Dynasties to mean “moment,” but actual instruments for moon and star time only appeared in the Qing Dynasty. How did people know the time at night before moondials and stardials? They relied on listening to the night watchman bang his clapper.
China had many ancient astronomers. The one we know best is Zhang Heng of the Eastern Han.
Zhang Heng advanced the celestial sphere theory of his predecessors and technologically upgraded the armillary sphere by adding a hydraulic transmission system. This new armillary sphere was called the Water-Powered Armillary Sphere; it could move on its own, automatically demonstrating celestial motions in chronological order—truly marvelous.
Of course, Zhang Heng’s most famous invention is the Seismoscope.
When the Zhengtong-era observatory was first built, some small rooms were certainly constructed so that the astronomy officials could rest after climbing the platform. That building still stands, from the Ming Dynasty. Because the observatory was in continuous use, the house has been constantly maintained and is in decent shape.
The main hall is called the “Ziwei Hall.” In ancient Chinese astronomy, the area around the North Star was called the Purple Forbidden Enclosure (Ziwei Yuan), and the plaque’s “Ziwei” implies observing the heavens. In ancient divination, there was also the “Ziwei Doushu” (Purple Star Astrology), a method of calculating a person’s fortune based on their birth date and hour, so the observatory also had the function of divining the royal fate and national destiny. Haha, see, I was right: these sky observers really did calculate the imperial fortunes.
Despite being an imperial office, the building’s architectural status is modest. From outside, it’s a five-bay hall with a plain gray-tile flush-gable roof. You see such roofs all over Beijing’s Dongcheng, Xicheng, even Xuanwu and Chongwen districts. The only hints of prestige here are the massive main ridge and the brick-carved chiwen ornaments at either end. Step inside, and it’s just a residential-style post-and-beam structure.
This hall houses an exhibition called “The Chinese Starry Sky.”
Inside are some precision instruments.
Up there is a Taxi Carriage—but you don’t pay by the distance you ride; it tells you how many li you’ve traveled. For every li forward, a wooden figure on the carriage beats a drum once. “Eight thousand li of cloud and moon”—imagine colorful clouds chasing the moon in this carriage, the wooden figure beating the drum 8,000 times. Why not just hire a living person to sit and drum? Who could stand that job? Endlessly drumming 8,000 times—who could bear it? This Taxi Carriage was another brilliant invention of Zhang Heng, predating Zhuge Liang’s wooden oxen and mechanical horses.
All these years, passing Jianguomen, I’ve always missed this ancient observatory. Today’s visit finally brought me face-to-face with its silhouette and the bronze instruments upon it—all of which, of course, are contemporary replicas.
