After finishing the simple dinner, Gao Wu cleaned up the mess. The moon had already risen.

Zhao Hao pointed the two-foot-long telescope towards the moon and asked the two of them to observe it in turn.

But this viewing experience is definitely not pleasant...

When the moon far away in the sky came before their eyes, they could clearly see that there was no sea, no forest, and no signs of life on the moon.

What they originally thought were the osmanthus trees, the moon palace, and the jade rabbit were all just bumpy circular valleys.

The moon that they imagined to be as bright as a silver plate and flawless turned out to have a big, pockmarked, scabby face.

"How could this be..." Wang Wuyang and Hua Shuyang looked at each other dejectedly. They really couldn't accept that the Moon Palace, which held countless beautiful legends, was actually a dead and barren land...

Zhao Hao’s previous experiments only aroused their interest in science, but now the observation of the moon directly challenges their worldview.

"There's nothing strange about this." Zhao Hao remained calm and said, "The moon is a bumpy planet like an orange. There is no Chang'e, no Wu Gang, no osmanthus tree, and even no water or air on it."

"The moon is a planet?" The two were afraid that they had missed something, so they ignored the shock in their hearts and quickly asked the teacher: "Master, what is a planet?"

"A planet is a spherical celestial body that moves in the universe according to certain laws." Zhao Hao said in a deep voice: "The sun, the moon, Mercury, Mars, Saturn... and the earth are all planets."

"If that's the case, why can we only see the full moon on the 15th of every month?" Wang Wuyang asked puzzledly: "For example, today, the moon is obviously missing a piece!"

"No!" Hua Shuyang slapped his thigh when he heard this, and hurriedly observed again: "I just saw a dark shadow on the waning part of the moon. If you count that dark shadow, the moon is still round tonight!"

"Really?" Wang Wuyang also leaned over to take a look, and indeed he could clearly see that the overall outline of the moon was round, but a part of it was blocked by something.

"What is covering it?" they asked in unison.

"I'll demonstrate it, and you'll understand." Zhao Hao said, holding a white ball the size of a pigeon egg next to the lamp. "Because the moon itself does not emit light, the so-called bright moonlight is just reflected sunlight."

The two looked at the orange ball with a confused look on their faces and whispered, "It should have always been a full moon."

"That's right, but I just said that all the planets are moving according to certain laws." Zhao Hao said, and took out a large ball painted blue, blocking the small ball representing the moon and the candle representing the sun.

Then Zhao Hao slowly moved the small ball to rotate around the big ball, clearly demonstrating the changes of the moon's waxing and waning to the two of them.

"The so-called waxing and waning of the moon actually refers to how much sunlight can be seen on Earth. This is because the moon revolves around the Earth. On the first day of the lunar month, it is between the Earth and the Sun, and we can only see the side that faces away from the sun, so we cannot see its existence with our eyes. On the seventh and eighth days of the lunar month, the moon moves to our side. At this time, we can see clearly from the Earth that it is dark in the east and bright in the west. This is the so-called 'first quarter moon'. On the fifteenth day of the lunar month, the moon moves to the back of the Earth again. At this time, we can see its complete side facing the sun, which is the day of the full moon..."

"I know!" Hua Shuyang suddenly realized, "Then it will continue to rotate, and when it reaches the 18th or 19th day, which is today, it will be dark in the west and bright in the east, and it will become a waning moon!"

As he said this, he clapped his hands and realized, "It takes exactly one month to complete one circle!"

"This young man is teachable." Zhao Hao nodded approvingly, then looked at Wang Wuyang and said, "He understands. What about you?"

"I roughly understand it, but I just follow what Master taught me..." Wang Wuyang pointed at the blue ball in Zhao Hao's hand and said in a trembling voice: "Don't we live on a ball too?"

"Yes, Master, isn't the sky round and the earth square?" Hua Shuyang asked in disbelief.

"Of course not." Zhao Hao took out the last teaching aid from the wooden box - a globe!

He turned the blue sphere that looked like a celestial globe, then gently pressed it and said to the two students, "This is the Earth we live on. Three quarters of it is covered by sea water, and the remaining quarter is land."

The two students stared at the blue globe and the land masses marked with different colors, and soon saw the location of the Ming Dynasty.

"Is our Ming Dynasty here?" Hua Shuyang came closer and looked carefully, "This insect-like place next to it, is it... Japan?"

"Ah, the Portuguese are here! They are separated from us by so many countries. It turns out that the Western countries are so far away from us?" Wang Wuyang shouted from the other side: "It is really not easy for the Portuguese sailboats to sail to the Ming Dynasty!"

"Yes, although I don't want to say this, I have to admit that the Western countries have gradually caught up with the Ming Dynasty, and even surpassed us in the fields of navigation, astronomy, mathematics, etc." Zhao Hao sighed and said, "For example, they were the first to discover and prove that the earth is round."

"How did they prove it?" Hua Shuyang asked in shock.

"A hundred years ago, the theory of the earth's roundness had spread throughout the Western world, but there were always people who didn't believe it. So forty or fifty years ago, a Portuguese captain named Magellan decided to sail around the world. Because if the earth is round, as long as he keeps sailing in one direction, sooner or later he will return to his starting point."

Both of them understood this logic, but they just nodded slowly and said nothing.

They were completely shocked by the feat of the great navigator.

Zhao Hao said to the two of them in a low voice, "In 1519, the 13th year of the Zhengde reign, Magellan, with the support of the King of Spain, led five ships and 270 sailors from the Spanish port of San Rocal and began the greatest expedition in human history!"

As Zhao Hao spoke, he slowly drew lines on the globe with a brush and said, "They first crossed the Atlantic Ocean in 70 days and arrived at the coast of Brazil. Then they went south along the coast, bypassed South America, and entered the Pacific Ocean. After sailing in the Pacific Ocean for more than 100 days, they arrived in Luzon."

"Luzon?" This place name was familiar to both of them. It had already entered the traditional sphere of influence of the Ming Dynasty.

"Then they crossed the Indian Ocean, arrived in Africa, went around the Cape of Good Hope, went north along Africa, and finally returned to Spain..." Zhao Hao expressed his respect for the pioneers in a low voice: "At that time, they only had one ship and 18 sailors left. Even Magellan himself had died on the way."

"But they used the most indisputable method to prove that the earth is round!" Finally, Zhao Hao raised his voice, looked at the two people with sharp eyes and said: "This matter is well known in the Western countries. You will definitely meet Western people in the future, and you will know the truth by asking them."

ps. The second guaranteed update is here, please give me your monthly votes and recommendation tickets~~~~