What Chen Muwu told Eddington was to calculate the distance of Andromeda from the center of the Milky Way by observing the Cepheid variable stars in the Andromeda Nebula.

As long as this distance can be determined, and then compared with the known radius of the Milky Way, we can tell whether Andromeda is a nebula contained in the Milky Way, or a galaxy outside the Milky Way, which is equivalent to the status of the Milky Way.

This method of measuring the distance of Cepheid variable stars was first proposed by the American astronomer Harrow Shapley.

In this way, he estimated the radius of the Milky Way in 1918 and was the first to point out that the Sun was not at the center of the Milky Way.

However, Shapley is a true proponent of the Milky Way One Theory, believing that the universe is the Milky Way, and that there are no other galaxies with equal status outside the Milky Way.

Edwin Hubble was inspired by Shapley's approach and began to make observations of nebulae such as Andromeda at the Mount Wales Observatory, hoping to find Cepheids and calculate distances.

At the end of 1924, Hubble published a large number of observational data, confirming that several "nebulae", including Andromeda, were in fact outside the Milky Way.

Thus proving the error of Shapley's theory, nebulae should not be called nebulae, but galaxies.

The astronomical problem that Chen Muwu mentioned was to ask Eddington to measure the distance of these nebulae from the Milky Way first, and then think that they would be the later map.

As for what is this post-image?

Of course, it is through the discovery of redshift to prove that the universe is expanding, and then overturn Einstein's static model of the universe!

Unexpectedly, after Eddington listened to what Chen Muwu said, he just smiled bitterly twice, then stood up and nodded to Chen Muwu on the sofa: "Come, Chen, you come with me." ”

The two walked out of the office one after the other, and Eddington led Chen Muwu into the dome of the Cambridge Observatory, pointed to a refracting telescope on the stand, and said: "Chen, this is the largest telescope in our observatory, it was donated in 1833 by the third Earl of Northumberland, who later became the Chancellor of Cambridge University.

"Yes, you heard it right, 1833, exactly ninety years ago.

"This 12-inch telescope was indeed a big thing in its time, but today, 90 years later, it is far behind the times.

"I actually knew about Shapley's method of calculating distances through Cepheid variables a few years ago. But what's the use of knowing? When Shapley observed Cepheid variables, the aperture of the telescope he used was already 60 inches.

"I heard that not long ago, a new 100-inch telescope was built at the Mount Wilson Observatory. People in the United States have a lot of money, and of course they have money to build telescopes.

"But we don't have any money at Cambridge University, and our annual funding for the observatory is basically only enough to maintain this ninety-year-old guy.

"Not to mention compared with the two behemoths above, even the rich American in Lowell, in order to find the mysterious planet X hidden in the darkness, spent money to repair the telescope in the observatory, the aperture is twice as large as that of the Northumberland!"

Eddington's hand gently caressed the old fellow on the shelf, and his words were filled with deep helplessness.

What he said was very clear, and Chen Muwu also understood that it seemed that with this telescope at the Cambridge Observatory, it would not be able to measure the brightness of the Cepheid variable in Andromeda no matter what, which meant that the distance could not be calculated.

His idea was in vain.

Only after Hubble publishes his observations next year can Chen Muwu build on his data, combined with Vesto Shriver's redshift spectral line, to point out that the universe is not static, but expanding.

In the dark, God couldn't bear to let Eddington break Einstein's dream.

However, Chen Muwu also found another useful information from Eddington's words.

Isn't the planet X he is talking about Pluto?

Historically, Pluto was only discovered in 1930.

Since the discovery of Neptune, there has been speculation that there should be a planet of the solar system beyond Neptune.

Because I haven't found it for sixty or seventy years, this planet that people love, hate, and can't find is now given a name like Roentgenium's rays, called Planet X.

However, for Chen Muwu, this is really "the same force of heaven and earth", and the physics university found that one after another was rushed to the door, and he couldn't think about it.

On a summer night in his childhood, when he was enjoying the cool outdoors with his parents, Chen Muwu inadvertently looked up and saw the summer triangle.

Since then, he has been interested in astronomy, and in part, this is one of the reasons why he chose to major in physics after the college entrance examination.

Although he later embarked on a path that had basically nothing to do with astronomy, he was always a member of the astronomical club during his college years, and worked as a volunteer docent at the local planetarium for four years as an undergraduate.

As an astronomy enthusiast, Chen Muwu can remember that the semi-major axis of Pluto's orbit is 39.482 astronomical units, the eccentricity is 0.2488, the apsis angle is 14.53 degrees, the orbital inclination angle is 17.16 degrees, the ecliptic longitude of the ascending node is 110.299 degrees, and the perihelion radiance angle is 113.834 degrees.

But he doesn't want to take that data right now and find Pluto in a telescope.

Because now, Chen Muwu's identity is still a newcomer who has never made astronomical observations, and China is also a poor country that does not even have a modern observatory.

The observatory on the Purple Mountain in Beijing will not be completed until more than a decade later.

If he found this planet X all at once without a teacher, it really does not conform to human cognition.

Just like criminals launder money, if Chen Muwu wants to successfully "discover" Planet X, he must give him this astronomical skill to be completely whitewashed.

So he pretended to have an expression of longing for the sea of stars: "Sir, I am also very interested in this planet X, from today onwards, can I come to you every few days and borrow this telescope for astronomical observations?" ”

"How long is a few days? Half a year? ”

Eddington obviously hadn't forgotten Chen Muwu in his heart about releasing his pigeons, but seeing that he had the intention of leaving Cavendish and returning to the embrace of astronomy, Eddington finally nodded and agreed.

He asked Chen Muwu if he had made astronomical observations before, and Chen Muwu said that he had only read some astronomy books, but had never actually operated large instruments.

After receiving this answer, Eddington asked Chen Muwu to first compile a literature reading report on Planet X, and after he passed the review, he would come to the observatory to participate in half a month of equipment training.

After this series of processes is completed, the refracting telescope behind him can be used by Chen Muwu every Sunday night, but he must be contacted in advance to confirm before every Friday.

"Yes, thank you, sir."

At this point, the last stone in Chen Muwu's heart was also put down.

Pluto's apparent magnitude is about 14, and the telescope that can observe the brightness of this magnitude must have an aperture of at least 250 millimeters, which translates into hateful imperial units, that is, about 10 inches.

Of the astronomical telescopes over 10 inches at the Cambridge University Observatory, there is only one 90-year-old Northumberland telescope.

If Eddington hadn't nodded and agreed to let him use the big telescope, but only provided him with a small telescope, then even if Chen Muwu looked at the stars and saw that his eyes were torn apart, he would not be able to find the planet X hidden in the darkness.

After deciding on this series of matters, it was time for dinner, and Eddington invited Chen Muwu to join him to the auditorium of Trinity College for a dinner with complicated etiquette.

Chen Muwu happily agreed to this invitation, but the two people next to the astronomical telescope seemed to have forgotten that in Eddington's office next to the dome, there was also a Dirac sitting on the sofa!

(End of chapter)