The Paper asked
All along, human beings have always been full of reverie and unremitting exploration of the distant universe. Rushing to the moon, punching mars, space travel, why have we never stopped exploring the universe? What kind of discipline is astronomy? In this issue, Wang Kaixiang, a doctoral student majoring in astrophysics at Peking University, is invited to look up at the starry sky and explore the universe together.
How the universe has evolved to this day
@Phi Xing Dai Yue EatIng Cantaloupe: Is the Emergence of Earthlings the Result of the Evolution of the Universe? Why do scientists believe that there are aliens in the universe?
Wang Kaixiang: Man is the result of the evolution of life on earth, and the emergence of the earth is also formed by the evolution of the universe. There are hundreds of millions of planets like Earth in the universe, so probabilistic estimates generally believe that there should be other life in the universe, but due to the limitations of the current observation ability, they cannot be found.
@Savage: The big bang of the "singularity" is a common view in today's scientific community, can you explain what the "singularity" is?
Wang Kaixiang: In the 20th century, Hubble discovered that the universe was expanding by observing extragalactic galaxies, so push back, how did the universe come from nothing? There should be a starting point for getting bigger from scratch.
@Surging netizen u2Eziq: Are there high-dimensional and low-dimensional spaces in the universe?
Wang Kaixiang: Our world is composed of four dimensions, three-dimensional space plus one-dimensional time. The higher dimensions exist mathematically, but it's hard to prove that they really exist in the physical world.
@Surging netizen mimYRb: Why is the solar system flat instead of three-dimensional circle?
Wang Kaixiang: To put it simply, the solar system originated from the protostellar disk formed by the accumulation and contraction of the initial nebula material, because the system has primordial angular momentum (in rotation), so the final formation is a pancake structure.
@oooody: Is it possible to get more efficient energy from the universe than solar energy? Is it possible to be more terrifying than nuclear energy?
Wang Kaixiang: The sun relies on internal nuclear fusion reactions to generate energy, and the mass-energy conversion efficiency can reach 0.7%. The supermassive black hole at the center of the galaxy absorbs the surrounding material, converting gravitational energy into light energy, which is an order of magnitude higher than nuclear energy.
@The Paper: What aspect of the earth may solar activity affect the earth in 2023? How can individuals prevent this in advance?
Wang Kaixiang: Solar flare outbreaks, coronal mass ejections and other activities may affect space weather, satellite equipment, radio communications, ground power, etc. Specific activity times are difficult to predict, have little noticeable impact on daily life, and do not require prevention for individuals.
The mystery of the stars
@Christy. Xiang: What are the stars in the sky made of?
Wang Kaixiang: Stars are hot plasma balls formed by the condensation and contraction of nebula material from gravitational attraction, with the highest core temperature, and the nuclear fusion reaction produces huge energy, radiating outward, becoming a bright luminous body. It is like a super "hydrogen bomb" with continuous and stable output.
@ Qingyang Laosuo: Are the stars that people see now just shadows from tens of millions or even hundreds of millions of years ago? Are some stars actually long gone? The light emitted by a star billions of light-years away from Earth has gone through so long distances and for so long, why can it still be observed on Earth? Doesn't its energy suffer loss and decline?
Wang Kaixiang: The stars that we can see with the naked eye are basically tens to thousands of light-years away. If a star is 100 light-years away, we are now receiving the light it emitted 100 years ago. The evolutionary history of stellar life usually lasts from tens of millions to tens of billions of years. The disappearing star you're referring to is probably a supernova explosion. The proportion of stars in this part is still very low.
The attenuation of light intensity is the square of the distance. When the distance is doubled, the light intensity becomes a quarter of the original. In fact, usually we can't see the light emitted by an ordinary star hundreds of millions of light years away, because the light intensity is too weak, so we can't distinguish a single star. As for the hundreds of millions of light-years, or even billions of light-years, we can see that the celestial bodies are generally composed of bright galaxies, supernovae, quasars, etc., which is the sum of hundreds of billions of stars' luminescence, not a single star.
@ZhuangZai my teenager: There are more stars in the universe than sand on Earth, according to what system do astronomers name stars? And the stars are moving, we can't locate each star, isn't it impossible to determine that a star is the original individual?
Wang Kaixiang: There are many stars in the universe, but only a few thousand can be seen by the naked eye, and only a very small part of the total number of stars in the universe can be distinguished by telescopes, and a few bright stars have their own names. Stars in constellations are usually numbered in Greek letters by brightness, such as the α Orion, β, and so on. Darker stars are numbered by surveying different catalogues. Stars do have their own spatial motion relative to Earth, and this information (self-propelled, apparent velocity) is also part of the observational data of stars, usually their movement in the sky is very small, and there will be no change in hundreds of years, even a very small number of fast-moving stars are also very easy to track.
@Little Rabbit: Now that humans observe the farthest distance of stars, are they subject to the limitations of observation instruments and equipment?
Wang Kaixiang: First of all, two stars of the same brightness, the farther stars will appear fainter, and the stars with stronger luminous ability can be seen by us at a longer distance. So the farthest star we want to see depends roughly on two factors: the brightness of the star itself, and how dark we can detect. The mass and luminous capacity of normal stars cannot be infinite, and the brightest stars are about 100,000 times brighter than the Sun. Supernova explosions, on the other hand, emit extremely intense light, up to 100 billion times the luminosity of the Sun, or even as bright as an entire galaxy. The supermassive black hole at the center of the galaxy also has a strong ability to absorb material to emit light, which is also known as the active galactic nucleus. The brightest supernovae and active galactic nuclei can be detected by humans at distances of billions or even billions of light-years. Another point is indeed the limitation of detection capabilities, involving the telescope aperture, exposure time, band, atmospheric skylight and other factors, generally speaking, the current darkest celestial body can be seen at about 30th magnitude, equivalent to one of 4 billionths of the 6th magnitude of the naked eye limit.
@ It's still difficult to change the name: why did astronomy create the 88 constellation? Is there any difference between it and the 12 signs?
Wang Kaixiang: On the one hand, the birth of constellations comes from the imagination and creation of the ancients, that is, hundreds or thousands of years ago, people imagined according to the connection of stars. Another use is to divide the sky zone for easy observation. In this way, a comet appeared in the sky in ancient times: Ursa Major/Scorpio or the official direction of so-and-so star, not to mention 60 degrees south-east or an altitude angle of about 50 degrees. Constellation 88 is all-day, based on the entire sphere. 12 constellations refer to the zodiac signs or zodiac signs, which represent the constellations that the sun will pass through in the sky during the year, so there is a difference between the two.
Why humans explore space
@donottag: Where is the best meteor shower observation site in China? What is the approximate number of meteors you can see per hour? Recently, the weather is not good, is Shanghai not visible?
Wang Kaixiang: The weather is sunny, the field of view is open, and the place with less light pollution can be observed. For example, the deserts, Gobi, grasslands and other regions of Inner Mongolia, Gansu, Qinghai and other provinces are relatively good observation points. The maximum number of dozens of them can be seen with the naked eye per hour. There are more rainy weather in the south, like the bad weather in Shanghai, Zhejiang, and it is completely invisible this year.
@ Is it really the first time I have heard of it: if you want to see the Aurora now, is there no drama?
Wang Kaixiang: The northernmost part of the country, Mohe, Xinjiang Altay and other places can occasionally appear aurora, the frequency is about less than 2-3 years. If you want to see the Aurora Or go to the Arctic or Antarctic region.
@ A Dumpling OQ: Is the threshold of astronomy high? Can I only graduate in astronomy in graduate school?
Wang Kaixiang: Not high, you can see the stars when you look up, and there are many learning resources available on the Internet. Astronomy graduation, like other majors, can do anything, and is not limited to astronomical studies.
@Book of New Music: Why should humans explore the universe? What are the benefits for humans?
Wang Kaixiang: Everything we have in our lives now is the result of exploration. From the astronomical point of view, map navigation, time, calendar, WIFI, camera CCD, CT and other technologies are the practical applications of astronomy.
@ Dumpling OQ: In recent years, Musk's SpaceX and Virgin have been selling space sightseeing tickets to the public, can those who buy tickets go to space in their lifetime? How long are we from space sightseeing?
Wang Kaixiang: Yes. At present, there is a lot of investment in space exploration, and various large projects are continuing to be launched. Now private aerospace has also begun to flourish. Trips to the space station have been around for more than a decade, and can be achieved with any money. The space tourism we are looking forward to is actually hoping that its cost will drop sharply, and it will be difficult to drop to a very low level in the short term, but it is still relatively possible to achieve a suborbital flight of a few million yuan like Virgin.
Editor-in-Charge: Ju Wentao
Proofreader: Ding Xiao