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Relative to the determination of latitude, the accurate estimation of longitude is too difficult. Pen × fun × Pavilion www. ｂｉｑｕｇｅ。 info Because latitude has a fixed reference, and that is the sun. However, the longitude is artificially prescribed, and the reference point is also artificially chosen, such as the prime meridian, which is prescribed as the meridian that passes through the Greenwich Observatory in the United Kingdom.

If you know the time on a certain meridian, it's easy to measure the local longitude. For example, if you know Beijing time now, as long as you do it the same way as latitude measurement, when the sun rises to midsky, see what time Beijing time is. The difference between that time and 12 o'clock is a reflection of the difference in longitude between the two places. Because the earth is divided into twenty-four hours, for every hour of time, there is a difference in longitude of fifteen degrees.

But now Zhu Youzhen has neither a watch, nor does he know the time in other places, so the above method is certainly not feasible. So he had to use one method that was extremely complex and much less accurate: stargazing!

Speaking of which, this trick was learned from Mao Wenlong when Phi Dao was bored. The principle is simple, that is, due to the difference in latitude and longitude of each observation point, the starry sky observed at the same time is also different. In terms of latitude, the starry sky near the North Pole is not visible in the Southern Hemisphere; Even in the Northern Hemisphere, the height of the same star varies with latitude, such as the North Star, which hangs high above the head forever when viewed from the North Pole.

Relative to the change in altitude brought about by latitude, the stars that rise in the east and set in the west like the sun due to the rotation of the earth are even more difficult to grasp. Even if you look at the same star at the same observation point, it will be in a different position in the night sky depending on the time of day.

At that time, Mao Wenlong was keen on the study of astrology, except for the night of the indulgent drinking carnival, almost every night he had to pull Zhu Youzhen, a fake Maoshan Taoist, to watch the heavens at night, and discuss with him the major events in the world corresponding to the astrology.

Zhu Youzhen knew that the so-called "there was such and such a thing in a certain place in a certain astrological sign" was pure nonsense, and he didn't take it to heart. However, he was originally interested in astronomy, and he listened to Mao Wenlong talk about which star was called what name and which star it belonged to, and he also listened to it with relish. Because in the previous life, the division of the stars in the night sky was completely according to the western constellations, and almost no one knew about the three walls and twenty-eight sutras handed down from the ancestors.

It was night when Zhu Youzhen and Li Zhenyan held hands and climbed to the top of the island again. The two sat side by side on the tallest stone, looking up at the vast night sky.

"Your Highness, the night sky is so beautiful!" Like a child, Li Zhenyan sincerely admired, "No matter how the world changes, these stars will always hang in the sky, day after day, year after year." I remember the poem "Tengwang Pavilion" by my Wang Bo, the bishop of Lishan County, which contains 'The shadow of the idle cloud pond is long, and the stars change a few degrees of autumn; Where is the emperor in the cabinet now? The Yangtze River is empty and artesian outside the threshold'. In another thirty or fifty years, I don't know if Zhenyan will be able to look up at the starry sky with His Highness like tonight! ”

Zhu Youzhen was also quite emotional, and hurriedly hugged Li Zhenyan tightly in his arms and said: "Zhenyan, I promise you, as long as it is in your lifetime, every year today, I will accompany you to see the stars!" ”

As he spoke, a meteor flashed in the sky with a long tail. Zhu Youzhen lived in the city in his previous life, and with air pollution and light pollution, he may not be able to see even the brightest stars, let alone the fleeting meteors, and he can't help but excitedly point it out to Li Zhenyan.

Li Zhenyan hurriedly clasped her hands and bowed her head in silent prayer. When the meteor disappeared into the night sky, she smiled happily: "When Zhenyan was a child, I heard my mother say that if you make a wish on a meteor, your wish will definitely come true." I've made a wish just now, and it's up to me to see if it works! ”

"What wish did you make?" Zhu Youzhen asked curiously.

Li Zhenyan winked at Zhu Youzhen slyly and said, "I can't say it, it won't work if I say it." ”

Zhu Youzhen didn't feel it, and looked up at the starry sky again, only then did he remember that he only cared about enjoying the minutes and seconds with Li Zhenyan, and almost forgot about the business. So he stopped talking, and calmly observed the starry sky carefully.

With the guidance of the Big Dipper with the spoon handle slanting westward, Zhu Youzhen quickly found the North Star, and determined the position due north. Then, according to the position of the 28 Nakshatras in his memory, he looked for the corresponding stars from the night sky.

It is clearly visible from the night sky that in the northern half, except for the height in the night sky, these nakshatras are about the same as those seen from Phi Dao. It's just that the North Star is very low, just a little above sea level. And the night sky in the southern half is mostly constellations that Zhu Youzhen has never seen.

Zhu Youzhen hurriedly asked Li Zhenyan: "What time is it?" ”

Li Zhenyan has been following Zhu Youzhen's instructions today, taking noon as the benchmark and silently estimating the passage of time. At this time, he hurriedly said: "It's about a moment now." ”

Zhu Youzhen thought to himself that the hour was half past nine in the evening, which was roughly the same time as the time he spent stargazing on Phi Island. He hurriedly carefully observed the positions of the stars in the northern sky, and compared them with the positions of the stars he saw in his mind on Phi Dao.

In this comparison, Zhu Youzhen was pleasantly surprised to find that in addition to the difference in height, the angle of these stars in the night sky is basically the same as that seen in Phi Dao! In other words, the island you are on is about the same longitude as Phi Island!

He hurriedly carved the stone with the faint starlight. Li Zhenyan asked curiously, "What is His Highness drawing?" ”

"Map of East Asia!" Zhu Youzhen pointed while excitedly saying to Li Zhenyan, "Look, this is Phi Island, draw a line from Phi Island to the south, and the small island where we are located is almost on this line!" plus twenty-five degrees north latitude obtained during the day..."

Zhu Youzhen's hand suddenly stopped, because he found that the two lines intersected in the ocean not far east of the island of Taiwan, and the position was slightly northerly.

He suddenly seemed to realize something, and muttered, "I should have thought of it, I should have thought of it a long time ago... Zhenyeon, I'm not going to sleep tonight, I'm just waiting here for dawn! You go back to the stone hut and sleep. ”

"Your Highness won't leave, and Zhenyan won't leave, I'll accompany you here." Li Zhenyan didn't know why, but she also knew that Zhu Youzhen must have made a major discovery, so she sweetly pillowed her head on Zhu Youzhen's shoulder and accompanied him silently. After a long time, Li Zhenyan fell asleep unconsciously.

By the time she woke up again, it was dawn. I saw Zhu Youzhen jumping and jumping on the top of the mountain like crazy, and pointed to the surrounding islands that had just emerged from the fog, and shouted to Li Zhenyan: "Do you see those small islands?" I'm dumber than a pig, I should have thought of them when I saw them! ”

Speaking of this, Zhu Youzhen actually howled excitedly. Li Zhenyan was startled, and hurriedly got up to support him and said, "Your Highness, what's wrong with you?" Do you know where this island is? ”

Zhu Youzhen let tears flow wantonly on his face, and looked up to the sky and shouted: "! This is! ”