Throughout the long history of mankind.

The debate over the correctness of the round Earth theory and the flat Earth theory has always been a highly controversial topic.

Previously, when introducing Zhang Zai, the origin of the round Earth theory was mentioned:

It is generally believed that the round Earth theory officially appeared in the 6th century BC.

That is when the Ancient Greek mathematician Pythagoras first proposed the concept of the Earth.

Then by the 3rd century BC.

The scientist Eratosthenes, living in Alexandria, established the concept of the Earth using geometric methods and calculated the Earth's diameter.

However, what was not mentioned at the time is that Eratosthenes's method was actually quite clumsy:

He accidentally learned that on the summer solstice every year, the Sun's rays would directly hit the bottom of a deep well in Sai, which is in Aswan, Egypt.

At the same time.

In Alexandria, about 5000 Greek miles directly north of Sai, there was an angle of 2π/50 radians, or 7.2°, between the Sun's rays and the perpendicular line to the ground.

Assuming the Sun's rays are parallel.

Then, based on the formula for circumference, a value could be derived:

The Earth's circumference along the meridian passing through the north and south poles = 5000×2π÷2π/50 = 250000 Greek miles.

This is just a theoretical deduction that only unified some people's understanding.

In reality, the round Earth theory did not KO the flat Earth theory with one punch as soon as data or formulas were solved.

Throughout human history.

Almost every dynasty has had people who did not believe in the round Earth theory.

Even in the later 21st century, supporters of the flat Earth theory are not uncommon.

For example, now every year there is a flat Earth conference held across the sea — the recent one had over 600 people attending in person.

The online attendees reached 124,000 real people, and the domestic live streaming platforms easily had millions of viewers.

YouTube is also filled with various videos claiming to prove the Earth is flat.

Nowadays, local amateur scientists are considered a pejorative term, like seeing all sorts of designs resembling the Eight Trigrams in architectural drawings, or scribbles akin to Xu Yun's calligraphy.

But in front of flat Earth supporters, these amateur scientists hardly hold up.

Flat Earth supporters believe the round Earth theory is a complete hoax:

The photos of the Earth from outer space are fake images taken by rulers to confuse us, a pseudo-truth to enslave humanity.

Among them, NBA star Owen is a well-known flat Earth supporter.

To be precise.

He is a 'believer' of the "Pacman Sect":

This sect believes the Earth is flat, and if you reach the edge of the Earth, you will instantly appear on the other side, preventing you from discovering the Earth is flat…

Kangaroo Country is the opposite nation, there was even a time when a singer with minor brain atrophy was revered by them as a defective product of stopped time.

By the way.

Another star, Curry, believes the moon landing is fake, a complete hoax.

Without exaggeration.

In the Flat Earth Sect, various bizarre statements are almost innumerable.

They fly the banner of not blindly trusting authority (which in itself is not incorrect), but engage in all sorts of anti-intellectual and even terrifying activities.

In reality.

The Flat Earth is a key point in the Communist Party's layout, as well as the core basis of conspiracy theories.

The details are too sensitive, so they will not be elaborated here.

In conclusion.

This world is far crazier than we imagine.

For posterity, it's already like this, not to mention the ancient times when the round Earth theory was not an axiom.

Let's talk about the three people in the room now:

Old Su, having drawn star maps as a professional astronomer, is more inclined to accept the round Earth theory compared to others.

He even inherently has some tendency to believe the Earth is round.

But Xiaoli and Xiaozhao are different.

Although these two young people are very interested in science.

They have never undergone any systemic and correct scientific education.

So when Xu Yun earlier mentioned that the Earth is round, they naturally developed some doubts in their hearts.

If it weren't for noticing Old Su listening with great interest.

Xiaoli might have already interrupted Xu Yun, angrily expressing skepticism.

In the room.

Looking at the excited Old Su and the confused Xiaoli, Xu Yun pondered for a moment and said:

"Master, have you been to the seaside? — I mean an ocean as vast as the eye can see."

Old Su nodded upon hearing this and recalled:

"Nine years ago, I was ordered to Deng Prefecture to investigate naval provisions, and I indeed saw the ocean.

Truly an endless water connecting to the sky, which left me almost speechless with awe."

Deng Prefecture.

Which is today's Penglai City in Ludong Province.

This place has the renowned Dengzhou Port, also the core stationing place for the Song Dynasty navy.

Penglai, adjacent to the Bohai and Yellow Seas, truly deserves to be called vast and boundless.

Then Xu Yun turned his head and looked at Xiaoli and Xiaozhao.

Xiaoli, after pondering for a moment, shook his head:

"My father once served as an official in Huang Prefecture, only having seen the river, not the sea."

Beside him, Xiaozhao glanced at Xiaoli and slowly said:

"Unlike Miss Li, I went to Changguo County two years ago to purchase medicinal herbs for Brother Wang.

Changguo is adjacent to the East Sea, so I was fortunate enough to witness the ocean's majesty."

Changguo during the Song Dynasty is today's Zhoushan in Zhejiang Province.

It is connected to the East Sea, also serving as an entry point to a vast world.

Two out of three people have seen the sea.

Though not a perfect ratio, it far exceeds Xu Yun's expectations.

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