Chapter 658: Let There Be Light

"That the moon is eaten is but its constant course" — Huan Tan believed this line from the Book of Songs, written a thousand years ago, showed that sages had long ago pointed out that lunar eclipses were ordinary events. And after entering the Han dynasty, with its vast territory and peace across the realm, observations of the sun, moon, and stars grew ever more meticulous.

He recalled that Sima Qian, in his Treatise on the Celestial Offices, had already summarized the patterns of lunar eclipses through the ages, hitting the mark with piercing clarity: lunar eclipses are constant; solar eclipses are inauspicious. The implication was that since lunar eclipses followed discernible patterns, they must be a "constant" phenomenon and could not be regarded as evil omens.

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But Sima Qian, after all, came from a Huang-Lao tradition, which after Emperor Wu of Han's reign was deemed "ideologically unsound," and his faint voice was drowned out by the ceaseless chatter of the Confucians and their prognosticatory apocrypha.

Ever since Han Confucians like Dong Zhongshu wove yin-yang and the five phases into the classics and established the doctrine of heaven-human resonance, occult learning had grown ever more rampant, and no one took Sima Qian's painstakingly crafted conclusions seriously anymore. At every lunar eclipse, the Gongyang school, the Ouyang Shangshu tradition, the Yi experts, the Qi Poetry scholars — each faction would rush to put forward its views, forcibly linking the event to the virtue of court governance, seizing the chance to strike at political rivals, and even compelling the Emperor to depose his empress or issue a self-condemning edict…

Huan Tan, an astronomy enthusiast and a staunch supporter of the "celestial sphere" theory, had long harbored doubts about lunar eclipses. But in those days there were no telescopes, making observation difficult, and the documents of the former dynasty had been collected by the academic gatekeeper Liu Xin and shrouded in secrecy. Neither Huan Tan nor Yang Xiong could access the exact records from past ages.

They had once gone to ask Liu Xin, but Liu Xin had declared with absolute certainty: "Sima Qian's words are erroneous. Lunar eclipses have no constancy."

Liu Xin, though entangled in politics, was a man whose scholarly authority none dared question, so Huan Tan believed him.

It was not until the fall of Wang Mang's Xin dynasty, when the former dynasty's documents fell into Diwu Lun's hands, and a search of Liu Xin's house for "protection" even turned up the old man's posthumous drafts and scattered writings for the Triple Concordance Calendar — much of which had never been made public — that Huan Tan, returning north and tasked with editing Liu Xin's surviving works, finally read a passage that made smoke pour from every orifice of his head!

"To project a lunar eclipse, set down the accumulated months of the gathered remainder years, multiply by twenty-three, and when it exceeds one hundred thirty-five, divide. For the remainder, add twenty-three to obtain one month; when it exceeds one hundred thirty-five, the number obtained, starting from the regular, counting outward, is the month of the eclipse…"

Huan Tan was utterly shocked: "So Liu Xin, back when he was compiling the Triple Concordance Calendar, had already calculated the lunar eclipse cycle based on historical records!"

This was no empirical summary or naked-eye estimate, but a complete, rigorous algorithm, deducing that in every 135 mean synodic months there are 23 eclipse seasons — on average, slightly more than two per year.

Yet Liu Xin, though just one small step from uncovering the truth, had stopped, and even concealed his results. During the Xin dynasty, he had never missed a chance to join the fray at every lunar eclipse, gleefully using yin-yang theory to attack his political foes.

After his anger subsided, Huan Tan quickly understood Liu Xin's motive: "One link in Wang Mang's return to the court was a lunar eclipse during the reign of Emperor Ai of Han, which the Wang clan and Liu Xin used to press their case, attacking the faction of the consort kin, Empress Dowager Fu and Empress Dowager Ding."

Though many years had passed, as long as Wang Mang reigned, if Liu Xin tore away that thin veil, where would old Wang Mang's face be? And Liu Xin himself was a devout believer in yin-yang, unwilling to admit that lunar eclipses were as ordinary as the sun rising and setting. So he could only deceive himself:

"Heaven-human resonance cannot be flawed — it must be my calculations that are wrong!"

So the old man pretended everything was as before and let these calculations sink into obscurity among the bamboo slips, until Huan Tan dug them out.

When Diwu Lun learned of this, he too was deeply moved, and thought to himself: "As expected — when scholarship gets entangled with politics, don't expect freedom or correctness."

That said, Diwu Lun's desire to strip away the fog of mystery from solar and lunar eclipses, and even from earthquakes, floods, and droughts — these "calamitous anomalies" — was itself politically motivated.

He liked everything to be within his control, but the heaven-human resonance doctrine always brought surprises. A realm this vast — how could every corner enjoy favorable weather? If any disaster anywhere in the territory was deemed proof of political moral failure, how could anything ever get done? Though Diwu Lun had already cracked down hard, scholars who devoutly believed in these ideas still quietly shaped public opinion, pointing fingers at anything they disliked. If the realm were unified, he could let them clamor, but with Wu and Shu still holding out, it would be disastrous if the enemy seized on such things to stir unrest and inflame popular sentiment.

So he chose to start with the easiest-to-calculate lunar eclipse cycle, to further undermine apocryphal theology and make the spectacle of Liu Xiu and Gongsun Shu next door dancing like shamans at every disaster look like a joke.

Two years ago, in the third month of the seventh year of Wude, Chang'an had experienced a solar eclipse and a lunar eclipse on the same day, throwing the people into panic. The authorities' denials had little effect — advance prediction was essential. The lunar eclipse cycle in Liu Xin's Triple Concordance Calendar did indeed contain errors and could not be fully precise; Huan Tan had to recalculate it from scratch.

A hair's breadth error leads to a thousand-mile divergence. Diwu Lun therefore gave Huan Tan's observations his full support, ordering the workshops to fire more transparent glass and improve the telescopes, gradually increasing their magnification…

Huan Tan drew step by step closer to the "truth" he sought. To prove to the scholars of the Imperial Academy that the moon's waxing and waning was not a swelling and shrinking of its volume, Huan Tan conducted an observation.

That night, the sky was clear, the stars glittered, and a crescent moon floated through the night. Huan Tan led a hundred scholars of the Imperial Academy to the star-gazing platform of Weiyang Palace to observe the fifth lunar mansion of the White Tiger of the West, a bright star called "Net Moon Crow," and watch how it was gradually obscured by the approaching crescent moon.

When "Net Moon Crow" and the moon drew close, with just a sliver of gap remaining, "Net Moon Crow" abruptly vanished. This scene was observed simultaneously through more than ten telescopes, with court painters recording it alongside. Huan Tan precisely measured the moment of "Net Five"'s disappearance, calculated incontrovertible data, and proved that those slivers of gap were all portions of the moon's darkened surface — "Net Moon Crow" had been obscured by the shadow of the moon itself.

The moon's waxing and waning has nothing to do with its size or volume. That being so, lunar eclipses must be a similar case!

In the end, Huan Tan determined that 28 lunar eclipses occur in roughly 19 years. When this result was presented on Diwu Lun's desk, Diwu Lun asked him if he was certain, because according to Huan Tan's projection, the next lunar eclipse would occur on the fifteenth day of the twelfth month of the ninth year of Wude. This time, Diwu Lun did not intend to be as passive as two years ago — he would announce the prediction in advance!

"When the time comes, Liu Xiu and Gongsun Shu will surely be struck with terror, beating drums and shooting arrows at the sky to save the moon. I alone will regard it as ordinary, like the moon rising and setting, waxing and waning."

Diwu Lun's expression grew solemn: "But if an error occurs, and the day of the eclipse is wrong, I will be doubted by the people, and worse, ridiculed by all under heaven!"

"Junshan, can you guarantee that this calculation is without error?"

Meeting Diwu Lun's gaze, Huan Tan, under immense pressure, replied: "Your servant has observed the stars for over forty years, gazed at the moon through a telescope for seven, and calculated the lunar eclipse cycle for several more. I have computed it over and over. I dare not be precise as to the hour or the minute — but the day of the eclipse, I am absolutely certain will not be wrong!"

Though he had been quite confident at the time, when the day of the eclipse actually arrived, Huan Tan was still extremely tense. From nightfall, he and his students craned their necks at the night sky until their necks ached, yet no erosion of the moon occurred.

Just as the water clock approached the zi hour and the day was about to end, with his prediction on the verge of failing, the lunar eclipse finally, unhurriedly, began. Only then did Huan Tan feel as though he had been granted a great pardon. He stepped back, leaned against the wall to keep himself from collapsing, and basked in the cheers of the crowd.

A great part of humanity's fear of nature stems from the unknown. When people know that a thing follows a predictable pattern and will not greatly affect their lives, that terror of the moon being devoured by a monster dissipates considerably.

Instead, a thought would spontaneously arise in their hearts: As expected, everything is within His Majesty the Emperor's grasp!

After catching his breath, Huan Tan could not help feeling smug. Though it had nearly expired, his calculation and prediction had, after all, come true. The way people looked at him was utterly changed, and Huan Tan, a little light-headed, came before Diwu Lun to claim credit.

"Your Majesty, since the lunar eclipse has occurred as calculated, proving it to be a regular event, should not the gold Your Majesty promised to allocate to the Bureau of Astronomy also be delivered?"

Diwu Lun laughed heartily: "That is only natural."

The Emperor ordered the Privy Treasurer to swiftly disburse the funds to the Bureau of Astronomy, but then he beckoned Huan Tan closer and, with a somewhat mischievous smile, asked: "Isn't Junshan celebrating a little too early?"

Huan Tan froze: "What does Your Majesty mean?"

Diwu Lun smiled: "Now we know that lunar eclipses are regular events. If placed within the celestial sphere theory, how would you explain them?"

Huan Tan was instantly stunned. Right!

According to the celestial sphere theory, lunar eclipses simply could not be explained — yet now he had precisely calculated their cycle.

Diwu Lun's words were soft, spoken only to Huan Tan, but they struck like a moon crashing violently into Huan Junshan's heart, overturning the astronomical theories he had held for fifty years!

"Since the lunar eclipse cycle is correct, then…"

"Could it be that the celestial sphere theory… is wrong?"

…

Just a few years ago, Huan Tan had been indignantly mocking Liu Xin's obstinate refusal to change, how he ignored the facts of the lunar eclipse cycle just to force-fit his yin-yang apocrypha.

But now, it was his turn to make this agonizing choice.

"How could the celestial sphere theory be wrong?"

To him, the celestial sphere theory was a matter of faith! Huan Tan had fought for decades against the astronomers and old Confucians of the Han and Xin dynasties to promote it, and had even, through his own arguments, persuaded Yang Xiong, who had originally believed in the canopy heavens theory, to join his camp.

Yet even Huan Tan had to admit that, after acquiring a telescope and extending his gaze farther, gaining a deeper understanding of the sun, moon, and starry sky, the once seamless and flawless celestial sphere theory now seemed to show a crack.

For instance, he had once observed that distant Mars and Venus, seen through the telescope, actually sprouted teeth, much like a small moon.

But Huan Tan was not so easily convinced. He quickly added a "patch" to the celestial sphere theory.

After leaving the star-gazing platform and returning to the hall, Huan Tan pestered Diwu Lun, chattering away, determined to prove his theory was not wrong.

"The celestial sphere theory that I and Ziyun propound goes a step further than the canopy heavens theory. The canopy heavens holds the sky to be a hemisphere, while the celestial sphere holds it to be a full sphere. The earth is like the yolk inside an egg, dwelling alone within the sky, while the sun, moon, and stars are attached to and move upon this 'celestial sphere,' which measures 365 and one-quarter degrees in circumference."

Diwu Lun nodded. To put it plainly, this was still a form of "geocentrism."

Huan Tan continued: "But even the celestial sphere theory does not hold the 'celestial sphere' to be the boundary of the cosmos; there are things beyond it. Now, to explain lunar eclipses, could we not say that the 'celestial sphere' is not a single plane, but layer piled upon layer — that beyond one heaven there is another, perhaps as many as nine heavens?"

"Qu Yuan's Questions to Heaven asks: At the juncture of the nine heavens, how are they placed and joined? The corners and bends are many — who knows their number? How do the heavens meet? How are the twelve divisions made? To what are the sun and moon attached? How are the arrayed stars arranged?"

"Therefore, your servant believes that rainbows, iridescent clouds, and mists belong only to the first heaven; the azure vault of the sky is the second heaven. Judging by the moon's orbital cycle, it may occupy the third or fourth heaven, relatively close to the earth. The sun, however, resides in the fifth or sixth heaven, farther from the earth. When the earth, moon, and sun move in their courses, they may at times obscure one another — and thus a lunar eclipse occurs!"

Remarkable! Diwu Lun realized that Huan Tan was indeed a man who could draw inferences from a single instance. These nine heavens really could be used to explain the earth's distance from the sun, moon, and stars. His painstaking efforts — tossing out bits of later-age knowledge from time to time to guide him — had not been in vain. But Huan Tan soon fell back into his own logical trap. His brows furrowed. Even so, it was still difficult to perfectly explain the occurrence of a lunar eclipse.

He was just a hair's breadth from the truth. Diwu Lun decided to push one step further and point Huan Tan toward a clear path.

"I recently acquired an ancient book, titled the Zhoubi Suanjing."

At this, Huan Tan's brows knitted even tighter. He immediately replied, "Your Majesty, that work was forged by fangshi of the Han era under the guise of antiquity. It is not a surviving text of the Duke of Zhou."

The reason Huan Tan reacted so strongly was that this book had been written by the school that championed the Canopy Heaven theory. Apart from its sections on mathematics, every part of it advocated for the Canopy Heaven theory.

"I know it is a forgery," Diwu Lun said. "But a stone from another mountain can polish jade. There is a passage in it that I found rather intriguing when I read it. Minister, please listen."

Diwu Lun had certainly not memorized it. He had the Palace Gentleman Dou Gu bring over that bundle of bamboo slips and ordered him to read aloud: "The sun is the essence of yang, comparable to the light of a fire. The moon is the essence of yin, comparable to the light of water. The moon contains a reflection; therefore, moonlight is born where the sun shines upon it, and its dark portion is born where the sun is blocked. When it faces the sun, its light is full; when it draws near the sun, its brightness is exhausted. The moon receives the sun's light and thus takes form and outline. Hence it is said the sun casts the moon's form; only then does moonlight emerge, and thus it becomes the bright moon."

Diwu Lun looked at Huan Tan, presenting the "correct answer" to him with utter directness.

"What this passage means is that the moon originally has no light of its own — it is only bright because it borrows the light of the sun!"