The Ming Dynasty: The opening scene features Zhu Di angrily accusing him of illegitimate succession.

Emperor Yongle accepted Lin Yue's policy of establishing overseas fiefdoms and expanding maritime trade, and despite strong opposition, he issued an edict to immediately establish the Treasure Shipyard Academy.

A few days later, the Baochuan Shipyard College successfully opened, with Lin Yue serving as a physics teacher, instructing Wang Jinghong, Chen Xuan, Li Zhaoxiang, Wu Fu, and others.

They were all people that Lin Yue had specifically requested to come. Some were eunuchs, some were officials, and some were scholars from the common people. They were all talented people who had made great contributions to the construction of the treasure ships in history.

To build massive ships that span thirty feet to navigate the Western Ocean and establish overseas vassal states to secure trade routes, what is needed are not craftsmen who adhere to conventions, but scientific and technological talents who understand the workings of nature, are knowledgeable about the world, and are good at innovation.

The lecture hall of the Treasure Shipyard Academy is located in a spacious wooden factory building by the river. A plaque with the words "Investigate Things to Attain Knowledge" hangs on the beam, and the floor is paved with neat bluestone slabs. Dozens of desks are arranged in an orderly manner.

Lin Yue, dressed in a blue official robe, stood in front of the platform, with a large white wooden board behind him, which was blank.

Zheng He, dressed in casual clothes, sat upright in the first row.

Zhu Gaoxu sat with his legs apart in the corner, while Zhu Gaosui looked around. Both of them had come to join in the fun while hiding their identities.

Zhu Di also changed into ordinary clothes and secretly observed Yao Guangxiao from a private room on the second floor.

Today is both the opening ceremony of the Shipyard Academy and Lin Yue’s first class at the Shipyard.

"Today we will not talk about shipbuilding. First, I would like to ask you all, what is the true nature of this world?" Lin Yue said in a clear and resonant voice.

The audience immediately began to whisper among themselves.

Lin Yue didn't waste any time and directly called on the particularly conspicuous Zhu Gaoxu to answer: "The one in the back wearing the red coat, the very tall one, you answer."

Zhu Gaoxu pointed to himself with a surprised look, and after receiving positive feedback, he simply opened his mouth and grinned.

"Is that even a question? It's naturally a case of a round heaven and a square earth."

Above, the heavens are like a canopy; below, the earth is like a chessboard; in all four directions, eight pillars support the sky. Is this not how the world is?

Many trainees with a background in craftsmanship nodded in agreement; this is the most widely circulated understanding among the people.

Lin Yue smiled but didn't answer, his gaze sweeping across the crowd before randomly pointing at someone: "What do you think, young man?"

"When Lin gave his advice, his subordinates thought that the theory of 'all-encompassing heaven' was more appropriate than the theory of 'covering heaven'."

Zhang Heng's "Commentary on the Armillary Sphere" states that the celestial sphere is like a chicken egg, the celestial bodies are round like bullets, and the earth is like the yolk of a chicken egg, residing alone within the heavens.

The sky envelops the earth, like a shell covering yellow, rotating day and night. Therefore, the twenty-eight constellations are half visible and half hidden, which aligns with what we see when observing the stars.

"Oh? What's your name?" Lin Yue raised an eyebrow. "How do you know you're compatible with stargazing?"

I randomly selected someone earlier, and I didn't expect them to actually have some real talent.

Knowing the theory of celestial spheres, even if it's not entirely correct, is at least far better than those pedantic scholars who only know how to quote classics. This is exactly the kind of talent the shipyard needs.

"Your subordinate is Huangfu Gui, and I work at the Imperial Observatory." Upon hearing this, Huangfu Gui stood up, bowed, and began to speak eloquently.

"For example, when crossing the ocean to observe the stars and measure the altitude of the North Star, the further south you go, the lower the North Star becomes. When you reach the South Sea, it becomes completely invisible."

If the heavens were truly flat and the earth square, the North Star should always be high in the due north, so how could it disappear?

Only when the earth hangs like an isolated egg yolk, and the celestial sphere rotates, can this phenomenon be explained.

Zhu Gaosui, intrigued, couldn't help but interject, "Then the earth floats on water? We're heading south, how come we don't fall in?"

The audience below laughed, and Zhu Di was quite surprised. If the world was really a sphere, why didn't the people below fall down?

There has been a debate between the "Covered Heaven" theory and the "Hollow Heaven" theory since ancient times, but no one has ever systematically demonstrated the theory. Most people just listened to it for fun and rarely thought about it seriously.

Lin Yue drew a perfect circle on the wooden board with charcoal, emphasizing the center: "You live in Nanjing, so you must have seen the sight of ships returning home on the river, right?"

He looked up at Zhu Gaoxu and asked.

"Have you ever thought about this carefully? If the earth were truly flat, the entire shape of a distant ship would be visible, so why is it always the mast that appears first?"

Zhu Gaoxu was taken aback at first, clearly having never associated this ordinary scene with the natural world and its structure.

His brows furrowed sharply, and he casually said, "What's so strange about that! It's just a matter of distance."

Distant objects are inherently blurry to the naked eye; tall masts naturally come into view first, while low-profile ships are seen later.

Moreover, using such a trivial matter to prove the theory of a celestial sphere is far too far-fetched.

Zhu Gaoxu snorted coldly, clearly disdainful of this theory of chaos.

"I followed my father... My father traveled all over the country, crossing countless rivers and seas, and he had never heard of the earth being round. If it were true as you say, wouldn't warships roll to the ends of the earth when they sailed? That's pure nonsense!"

Lin Yue was not angry upon hearing this, but instead spoke in a resounding voice.

"Regarding the theory of 'Hun Tian' (a concept in Chinese astrology), I will give you several irrefutable pieces of evidence, each and every one of which can be verified."

The first piece of evidence is the question about the ship's mast.

If the earth were flat, the distant ship would gradually shrink until it disappeared completely, rather than the hull disappearing first and only the mast remaining.

Lin Yue quickly drew a diagram on the wooden board and shouted.

"The ship's hull is not visible because it lies beneath the curvature of the earth!"

If you do not believe, you may send someone to sail a long distance and set up a marker on the shore to verify it yourself.

Your claim about the distance of the view is utter nonsense. You can use a Western telescope to see distant scenery.

If you observe with a telescope, you can still see the mast even after the ship has disappeared from view. Can this be explained by distance alone?

Zhu Gaoxu's brain was already overloaded, and he was unable to refute it.

Lin gave him no chance to catch his breath and quickly drew a diagram on the wooden board.

"Look, everyone, this is the arrangement of the sun, earth, and moon!" Lin Yue drew the positions of the sun, earth, and moon on the wooden board with his fingertips, connecting the three into a line.

"People are only amazed by the wonder of a lunar eclipse, but they do not know the truth of heaven and earth hidden behind it. Today I will explain it to you."

These words immediately enlivened the atmosphere.

Zhu Gaosui was greatly shocked and tugged at Zheng He's sleeve, exclaiming in a low voice, "Isn't a lunar eclipse just like a celestial dog eating the moon?"

Zheng He silently shook his head, indicating that he didn't know either.

He was just a eunuch who knew a little about warfare and navigation; he wouldn't understand any of this.

In a secluded private room on the second floor, Zhu Di peered through the window at the wooden planks below and asked curiously.

"Daoyan, you are well-versed in astronomy. Do you know the cause of this lunar eclipse?"

Yao Guangxiao, dressed in a plain monk's robe, clasped his hands together, his eyes showing a hint of surprise.

"Your Majesty, all I know is the deduction from the Datong Calendar."

According to the method of eclipse, one can accurately calculate the time and magnitude of a lunar eclipse, but never the cause.

Your subject suspects that the officials in the Imperial Astronomical Bureau probably only know the timing of the lunar eclipse, but not its cause.

The Ming Dynasty's "Datong Calendar" was inherited and improved from the Yuan Dynasty's "Shoushi Calendar". It could accurately calculate the date and time of a lunar eclipse, with a difference of no more than plus or minus one hour.

Zhu Di raised an eyebrow, his surprise growing even more: "Even you don't understand?"

"This Lin is merely a minor official who speaks out on matters of public opinion, yet he has some knowledge of astronomy. How can he be so confident that he can reveal such heavenly secrets?"

Looking down at the lecture hall, Zhu Di sighed with admiration.

"It seems I underestimated him, thinking he was just recklessly bold. His ability to solve problems that previous generations couldn't solve shows his extraordinary knowledge."

Fortunately, I did not kill this talented man in a fit of anger.