Stroll to the end of the universe

Our world has been spinning around a huge fireball year after year since it was born, and it is endless.

This is not an obvious fact-human experience from the earth is just the opposite-the earth seems to be eternal and stable, with the sun rising in the east and setting in the west, divided into day and night. The position of the sun is also reflected in ancient myths. It often plays a role that is important to the world but irrelevant to heaven. For example, in Greek mythology, the sun is just a golden ball in the hands of Apollo; In ancient China mythology, the sun was just the wheel on the carriage of the gods. In human daily experience, the size of the sun and the moon seems to be similar. This also creates obstacles for human beings to understand the relationship between the sun and the earth. People naturally think that the sun and the moon are celestial bodies with similar status, because they are almost far away from the earth from the visual point of view.

In order to study the motion of celestial bodies, ancient Greek astronomers put forward the concept of "celestial sphere". This is an imaginary sphere centered on the observer or the center of the earth. The sun, moon and stars at night can be marked on this sphere. The relative position of most stars on the celestial sphere seems to never change, so they are called stars. The starry sky revolves around the earth in a one-year cycle. For mid-latitude observers in the northern hemisphere, every summer night, bright Vega and Altair are always seen facing each other across the Milky Way near the zenith. In winter, Sirius, the brightest star in the whole sky, will appear in the southeast as scheduled. Ancient Greek astronomers divided the stars in the night sky into different constellations for people to remember. On the same night every year, the constellations in the sky are always the same (there are 88 different constellations in the whole sky).

Unlike other stars, the position of the sun on the celestial sphere will move. If we make the earth transparent and temporarily remove the atmosphere on the earth, we can see the stars in the whole sky at any time. We will find that the sun stays with the stars in Aries in April, moves to Leo in August, and moves from Ophiuchus to Sagittarius in the dead of winter. Every year, the sun passes along this line and passes through the constellation 13 1. This path of the sun on the celestial sphere is called the ecliptic, and the corresponding constellation is sometimes called the ecliptic constellation.

In addition to the moon, there are five celestial bodies on the celestial sphere, and their behaviors are obviously different from those of stars. They are Mercury, Venus, Mars, Jupiter and Saturn. These five celestial bodies are very bright and easy to observe with the naked eye. Venus, in particular, is the brightest object in the night sky after the moon, 20 times brighter than Sirius, the brightest star in the night sky. People call these five bright stars "planets" because, unlike stationary stars, their movements on the celestial sphere are obvious. For example, Jupiter's orbit around the celestial sphere is 12 years. The ancient astronomers in China called it the aged star, and based on this, they formulated the geochronology.

How to understand the motion of these celestial bodies? Astronomers in ancient Greece believed that the universe was actually composed of a series of concentric circles, with the earth as the center, and the sun, moon, mercury, Venus, Mars, Jupiter and Saturn, each celestial body occupied a layer of the universe and revolved around the earth on the concentric circles. Other stars collectively occupy the outermost sphere, which rotates around the celestial axis. This view of the universe reflects the philosophical thought at that time: the universe should be perfect and the celestial system should run smoothly forever.

However, the Greeks found a small problem in their "perfect" model of the universe, that is, the "retrograde" of the planets. This is a puzzling phenomenon in planetary motion. In the night sky, the trajectory of the planet on the celestial sphere is roughly from west to east. But at some point, people will observe that the speed of planetary motion will gradually slow down until it stops and moves in the opposite direction for a short time. In the near future, they will "twist their heads" again and set foot on the original track. In the "perfect" model of the universe, the retrogression of the planets seems irregular, but the Greeks had no choice but to mend the model of the universe. By about 140, this model became extremely complicated. Claudius Ptolemy, a Greek-born Roman astronomer, is recognized as a master of ancient astronomical theory. In his astronomical masterpiece "Astronomical Masterpieces", he showed the most advanced universe at that time. In this book, the earth has been slightly away from the center of the universe, and the orbits of all planets have become eccentric circles. In addition, each planet has its own small orbit, which is called "current wheel". This wheel runs in an eccentric circular orbit, and the planets run on this wheel.

Until16th century, Ptolemy's theory ruled the theory of celestial motion for more than 1000 years. This is very strange. Ptolemy's theory is complicated and not a pure geocentric theory. In fact, it violates the world view of perfect balance advocated by the ancient Greeks-the structure of eccentric wheel is more like a clever trick in the mechanic workshop, and should not appear in the sky created by the gods. But on the other hand, ptolemaic system did explain the motion and retrograde phenomena of the planets very well. /kloc-in the 6th century, mikolaj kopernik put forward a revolutionary theory of the sun center. In Copernicus's model of the universe, the sun is placed at the center of the universe, and all celestial bodies revolve around the sun. But half a century after Copernicus' death, Heliocentrism still could not overwhelm Ptolemy's geocentric theory. Judging from the accuracy of prediction, they are not much different. No matter which theory can accurately predict the motion of planets, the big planets always seem to go too fast at some time, and sometimes they go a little slower.

Figure 1. 1 Ptolemy's geocentric model, schematic diagram of earth and planetary orbits. Planets run on a small circle called the current wheel, and the small circle runs on a big circle called the even wheel. The center of the balance wheel is represented by a five-pointed star, slightly off the earth.

After all, the defects of geocentric theory are exposed step by step. /kloc-At the beginning of the 7th century, the telescope was born in the Netherlands. This instrument connects two lenses with a long metal tube. The first lens, called the objective lens, is used to collect and converge light. These rays are corrected by the second lens to form a real image that can be directly observed by human eyes. The ability of a telescope to collect light is proportional to the area of the objective lens. When the diameter of the objective lens increases by 10 times, the ability of the telescope to collect light increases by 100 times. Telescopes also enable observers to distinguish finer images, which is proportional to the diameter of the telescope. The human eye itself is a delicate optical system, but the area of light collected by the human eye is very small, which is roughly equivalent to the size of the pupil. This ability is enough for human beings to distinguish the enemies and harms in nature, and even to distinguish the tiny handwriting on parchment under dim candles or oil lamps. But when it comes to looking up at the starry sky, the ability of the human eye is limited after all. Early telescopes were very simple, but the area of the objective lens was dozens of times larger than the pupil of human eyes. Early telescopes greatly improved human vision.

1609, Galileo first applied telescope technology to astronomical observation. He was surprised to find that the Milky Way across the night sky was originally composed of countless stars. When he aimed his telescope at Jupiter, he found four small celestial bodies around Jupiter. Obviously, these celestial bodies are satellites that rotate periodically around Jupiter. Among them, the fastest rotating satellite can find its obvious displacement in one night. Since there are celestial bodies that can revolve around Jupiter, not around the earth, why does the sun have to revolve around the earth?

Johannes Kepler was born in Wildstadt, Germany, eight years after Copernicus died 1573/kloc-0. Kepler was poor when he was a child and was raised by his grandfather. His poor eyesight may be caused by smallpox when he was a child. In his life, Kepler rarely really sat in front of a telescope, but he was still regarded as a first-class astronomy expert in Europe, because Kepler had almost no rivals in mathematical calculation. Kepler is a follower of Copernicus, not only for scientific reasons, but also for theological motives. In Kepler's imagination, the world created by God must have perfect geometric characteristics. There are five different regular polyhedrons in geometry I * * *: regular tetrahedron, regular hexahedron, regular octahedron, regular dodecahedron and regular icosahedron. Every regular polyhedron always has an inner ball (the largest sphere that can be put in) and an outer ball (the sphere that just wraps the polyhedron). If five regular polyhedrons are nested, the space can be divided into six layers. Kepler thinks this is no coincidence. In his hypothesis, if the sun is placed at the center of the universe, the orbits of the six planets, namely water, gold, earth, fire, wood and earth, should just fit into a six-layer spherical shell divided by five nested regular polyhedrons (figure 1.2). How perfect!

1596, in Kepler's first astronomical work, The Mystery of the Universe, he enthusiastically described his perfect theory of the universe, supplemented by preliminary calculation results. However, European astronomers don't buy it. In more than half a century after Copernicus, the accuracy of astronomical observation has improved a lot. Kepler is still using the old data of Copernicus era to verify his theory, which is not appropriate. The quality of data has puzzled Kepler for many years. 1600, Kepler was invited by Tycho Brahe, the most famous astronomer at that time, to be his assistant in Prague. This is Kepler's dream opportunity.

Before the invention of the telescope, Tycho was probably the greatest observational astronomer. He transformed the sextant and Shibungi, greatly improving their angular resolution. Tycho can use his own modified instrument to study the motion of planets with the accuracy of 65438 0 minutes. Readers can straighten their arms forward, flush with their eyes and erect their index fingers. At this time, the angle that the index finger can cover is about 1 degree. Tycho's observation accuracy is 1/60 at this angle.

Figure 1.2 Kepler's original model of the universe. The orbits of the six planets, water, gold, earth, fire, wood and earth, should just fit the orbits defined by the nesting of five regular polyhedrons. The Mysteries of the Universe (1596)

Tycho devoted his life to measuring the motion of planets with high precision. When Kepler was invited, Tycho was a royal astronomer of the Holy Roman Emperor Rudolf II. His job is to compile the observations of planets accumulated in his life into a catalogue named after his patron Rudolf II. These data are just what Kepler needs. He was convinced that these data could prove his regular polyhedron model, so he embarked on a journey happily.

Tycho's cooperation with Kepler was not pleasant. Tycho has his own model of the universe, which is between Heliocentrism and geocentric theory. In this model, all the planets revolve around the sun and the sun revolves around the earth. Tycho hopes to use Kepler's mathematical talent to study his own model, but Kepler is a firm Copernican believer. Kepler couldn't get the whole picture of planetary motion from Tycho, because Tycho was wary of him and only generously provided him with a scale claw data bit by bit. Kepler failed to make progress in research, but spent a lot of energy writing articles attacking his research opponents for Tycho.

This cooperation is very short-lived. Six months later, Tycho died of a sudden illness. On his deathbed, Tycho finally handed over all the data to Kepler. He said to Kepler, "Don't let my life down."

In the following years, Kepler was finally able to solve the problem of solar system operation. He soon found that his regular polyhedron model had serious problems. This model can't predict the movement of mercury at all. The motions of other planets barely fit the model. Is Tycho's data wrong? Kepler refused to believe this reason. After working with Tycho, he fully believed in the accuracy of the data. Kepler had to admit painfully that there was something wrong with his "perfect" model of the universe. But he is not far from the real answer. After reviewing the data, Kepler found the key to solve the mystery-the orbit of the planet is an elliptic curve, not a perfect circle, and the sun is at a focus of the ellipse. This is Kepler's first law. Moreover, he also found the law that correctly describes the motion of the planet: the planet runs in an elliptical orbit, and when it is far from the sun, its speed will slow down; As it approaches the sun, its speed will increase. If we connect the planet and the sun in a line, the area swept by this line in unit time is always the same. This is Kepler's second law. A few years later, Kepler discovered Kepler's third law: the square of a planet's cycle around the sun is directly proportional to the cube of its semi-major axis. Kepler's research has achieved great success. From then on, as long as the position of the planet at any time is determined, according to Kepler's law, people can predict its subsequent motion completely and accurately.

Why do planets move like this? From 65438 to 0687, isaac newton finally found the mystery contained in Kepler's law-the law of universal gravitation. Newton believed that there is a force of mutual attraction between any two objects in the universe, and the magnitude of this force is inversely proportional to the square of its distance. Kepler's law of planetary motion is a direct corollary of Newton's law of gravity.

The great discovery of musicians

At the end of 18, the movement order of the solar system was established, but human understanding of the solar system itself was not sufficient. People still don't know whether there are only five planets in the sky or where the edge of the solar system is.

178 1 In March, an astronomer named William Herschel discovered a strange celestial body with his telescope. At that time, Herschel was systematically studying the binary stars in the night sky. Most of the targets he observed were stars, which were very far away from the earth. Even in a telescope, they are point illuminators with no specific shape. However, the celestial body discovered by Herschel showed a hazy spot at a magnification of 200 times. When he put on an eyepiece with a higher magnification, the size of the spot became larger. Herschel guessed that this celestial body might be a comet. But unlike ordinary comets, this celestial body does not have the long broom tail common to comets. As a precautionary measure, Herschel still called this celestial body a comet and informed the astronomical colleagues of the Royal Society of this discovery. At this time, Herschel didn't realize that this was the first prize of his great astronomical adventure.

In fact, a few years ago, Herschel was widely known in Britain as an organist and composer. He was born in a musical family in Hanover, Germany, with as many brothers and sisters as 10. Father Isaac Herschel is an orchestra player. Although my father is not a rich man, he decided to let all his children (at least all boys) receive a good education, not only music, but also science and mathematics. According to caroline herschel, Herschel's sister, after dinner, her father and Herschel discussed about music performance for a long time, but sometimes, the topic suddenly shifted to philosophy and science. The names of Newton, leonhard euler and William Leibniz appear frequently. The atmosphere of discussion will become very lively, especially William Herschel. Sometimes the discussion is so intense that mother has to intervene so as not to disturb the children who are going to school the next morning.

Under the influence of family education, Herschel became an excellent organ and oboe player, and gained a permanent position in the orchestra. Because of the war, at the age of 19, Herschel left Germany and went to Britain to develop his own music career. 1766, he received an invitation from Bath Octagonal Church to become a permanent organist of the church. Bath is a famous fashion and leisure city in Britain, and many generous celebrities are willing to provide sponsorship for musicians. Handsome appearance and superb technology made Herschel quickly emerge in the circle. As a musician, Herschel not only achieved a superior life, but also reached the peak of his career in Bath.

Summer is a busy season for musicians, who need to cope with different performances. Bath is crowded with tourists. But in winter, it becomes quiet and leisurely here. Herschel has enough personal time to regain his interest in astronomy. At the age of 35, Herschel accidentally bought James Ferguson's academic monograph Astronomy, which rekindled his interest in the mysterious night sky. After dinner, he often takes this book back to his bedroom and lets his daydreams about the starry sky and the universe accompany him to sleep. At this time, Herschel is no longer satisfied with Kan Kan as a science lover at the salon as he was young. He wants to observe the wonderful night sky described in the book for himself. This means that he needs a telescope.

After Galileo made his own telescope for astronomical observation, the technology of making telescope has made great progress. In Herschel's time, telescopes could already be bought from optical equipment stores, but they were expensive. There happens to be one in Bath's optical equipment store. However, the aperture of the telescope is too small to meet Herschel's expectations. Herschel wants to see the starry sky that no one else has seen. What he wants is the best telescope of his time. According to his plan, the mirror surface of this telescope should reach at least 20 inches (about 50 cm). Therefore, the self-made telescope became his only choice.

Herschel had some experience in making musical instruments when he was a child, but optical telescopes are completely different things, which require extremely high design and processing accuracy. No one knows why Herschel became a great telescope manufacturer. At first, it seemed that all the references were just robert smith's optics. But after some initial unsuccessful attempts, Herschel quickly mastered the skills of making telescopes. Grinding mirrors is a very monotonous physical activity, but Herschel's concentration is amazing. He can even work continuously 16 hours. His sister Caroline had to feed him with a spoon while he was working to avoid fainting at work.

Herschel has made a series of telescopes of different sizes. The most commonly used mirror has a diameter of about 50 cm and a focal length of 7 meters. Although a self-taught novice, Herschel's telescope is actually the best work of the whole era, far exceeding the small optical equipment used by his colleagues who chase comets. In fact, before long, astronomers all over Europe dreamed of having a telescope made by Herschel.

Whoever has the biggest telescope can make the biggest discovery, which is the iron law of astronomical research. 178 1 year, Herschel discovered this strange celestial body, which was his first major award. Astronomical colleagues of the Royal Society followed up Herschel's observation, and they soon found that the orbit of the new celestial body was a nearly circular ellipse. This means that new celestial bodies are not comets, because comets always run in very flat orbits. Finally, the astronomical community admitted that the celestial body discovered by Herschel was actually a planet, which is what we call Uranus today.

In fact, looking back at historical data, people found that Uranus had been observed and recorded by different astronomers before, but they didn't realize that Uranus was a big planet. This is because Uranus is much darker and moves much slower than other planets. The brightness of Uranus is about 6, but it is almost invisible to the naked eye. Its distance from the sun is 18 times that of the sun, and it only orbits the sun once every 84 years, so it is difficult for scientists to notice its movement. But in Herschel's large-aperture telescope, the shape of Uranus makes its real body known.

Herschel's discovery made the whole scientific community boil. This is the first time in human history that a new planet has been discovered independently by an individual. Herschel expanded the territory of the solar system by himself. Herschel was awarded the membership of the Royal Society and the Copley Medal. As the undisputed discoverer, he was asked to name the new planet.

Herschel dedicated the honor of discovering new planets to King George III of England. The king loves science, and Herschel hopes that the new planet will help him get the position of royal astronomer. However, the name "George Star" finally failed to gain a foothold in other countries. In France, scientists prefer to call this new planet "Herschel". After several games, astronomers accepted the name of this new planet "Uranus". This name comes from the name of the god of the sky in Greek mythology, the god of Uranus, which is translated into Uranus in Chinese. Astrology also quickly accepted this new planet and incorporated it into its theoretical system. Astrologers designed a unique symbol for Uranus-the initials H of Herschel's name on a round sphere.

Although the name "George Star" is only popular in Britain, it did not unexpectedly make Herschel popular with the royal family. He was invited to Buckingham Palace as a guest of honor for the king of England, and was also invited to watch the opera with the royal family. His telescope was also transported from his hometown to Greenwich Observatory, so that the king himself could see the stars named after him. After seeing Herschel's telescope, colleagues of the Royal Astronomical Society were no longer interested in their original antiques and asked Herschel to make new telescopes for them. Herschel is also willing to make a profit by selling telescopes. About 60 telescopes have been sold to colleagues in the Royal Society and astronomers in continental Europe. As an astronomer and a maker of top telescopes, Herschel is also. Herschel made a series of important discoveries in his life: he discovered a new big planet-Uranus; He (with his sister and son) established the largest complete list of nebulae and clusters in history, which is still in use today; He made a complete list of binary stars and proved that a large proportion of binary stars are not only visually but also physically interrelated. He discovered the existence of infrared rays ... at the end of this book, we will also see Herschel's name. Now, let's continue to explore the frontier of the solar system.

The frontier of the solar system

The discovery of Uranus led astronomers to speculate that there may be large planets outside our solar system. After all, the mass of the sun is very large, hundreds of times greater than the combined mass of all the major planets, and it can completely control more celestial bodies dozens of times away from the sun than the earth. It can be predicted that planets other than Uranus may look darker than Uranus and the period of revolution is longer, but astronomers can still look for suspicious candidates by carefully surveying the sky.

Surprisingly, however, the evidence of the existence of the next big planet was discovered by a mathematician, and the clue was hidden in the movement data of Uranus. In Kepler's solar system model, the planets all run regularly in their elliptical orbits and do not interfere with each other. In addition, we know that this is only a simplification of the actual situation. Because Newton's law of universal gravitation points out that there will be gravitation between any two celestial bodies. Different planets have different period of revolution, so they will approach each other periodically. When two big planets are close to each other, their gravity will slightly deviate from each other's perfect elliptical orbit, which is called "perturbation".

The discovery of Neptune is attributed to the outstanding mathematical ability of French astronomer Yu Erban Jean Joseph Le Verrier. After the discovery of Uranus, some mathematicians and astronomers realized that Uranus' orbit seemed to be disturbed by another big planet. Levi accurately calculated the size, orbit and position of this possible celestial body. At his repeated request, the Berlin Observatory discovered this giant planet in his predicted position, and Levi named it Neptune after Neptune, the god of the sea, according to the convention of naming other planets.

Mercury, Venus, Earth and Mars are collectively called Earth-like planets. As the name implies, such a planet, like the earth, has a solid surface and an iron core. Jupiter, Saturn, Neptune and Uranus are much bigger planets than the earth. In the past, people generally referred to these four planets as woody planets, but now we know that these planets can be divided into two categories: "gas giant planets" such as Jupiter and Saturn, whose main components are hydrogen and helium; Neptune and Uranus are "ice giants" mainly composed of frozen water, ammonia and methane.

Are there any big planets besides Neptune? We haven't found it yet 1930, American scientist clyde william tombaugh discovered Pluto. This is a small celestial body outside the solar system, about 40 times the distance from the sun to the earth, and its mass is only 1/6 of that of the moon. In the following 70 years, Pluto was defined as the ninth planet of the sun. But people found that Pluto was different from the other eight planets from the beginning. The orbits of the other eight planets are very close to a circle, while Pluto's orbit has a large ellipticity and even intersects Neptune's orbit. Sometimes Pluto will be closer to the sun than Neptune. More importantly, Pluto's mass is too low to dominate its own orbit. Since Pluto was discovered, the debate about its status has never stopped. Astronomers have been discovering small celestial bodies outside Pluto since the 1990s. In 2005, it was found that Eris (Venus, 136 199 Eris) was heavier than Pluto. This became the last straw to overwhelm Pluto's status. At the annual meeting of astronomy in 2006, astronomers issued a new definition of planet by voting, requiring that the celestial bodies orbiting the sun must be massive enough to clear other celestial bodies in orbit before they can be called planets. On the other hand, Pluto is only a little bigger than its moon, so it is stripped from the team of planets. Astronomers have created a new niche classification of "dwarf planets" for the largest celestial bodies in the asteroid belt, such as Pluto, Mars and Ceres. This kind of voting aroused strong public opposition at that time, but with the deduction of time, people gradually accepted this new and more reasonable classification method.

There are still a large number of small celestial bodies in the orbits near Pluto and Mars. Together, these celestial bodies form a disc-shaped region, which is called the Kuiper Belt. Although celestial bodies such as Pluto and Mars are mainly composed of rocks and metals, most small celestial bodies in the Kuiper Belt are composed of frozen water, ammonia and methane, similar to comets. Most of these small celestial bodies revolve around the sun year after year in the Kuiper Belt, but a few small celestial bodies occasionally wander to the central region of the solar system. When these small celestial bodies are close to the sun, the light and heat of the sun will sublimate the ice and form a long tail behind the small celestial bodies. At this time, the small celestial body becomes a comet. Comets have always been synonymous with bad luck in human history. In China, the appearance of comets is considered to be accompanied by war. Even at the beginning of the 20th century, people still felt panic because the tail of Halley's comet swept across the earth. Comets, like asteroids, play the role of human killers in all kinds of science fiction movies. In the movie Coherence, comets even play the role of connecting parallel worlds. However, the debris separated from the main body of the comet is the source of the beautiful meteor shower on earth. When the earth moves through the orbit of a comet, these fragments fall into the earth and form a meteor shower in the process of rubbing against the atmosphere.

The location of the Kuiper Belt is 40-50 days from the center of the sun, and the distance between the sun and the earth is 3, but this is not the boundary of the solar system. The entire solar system is actually wrapped in a structure called "Oort Cloud". Oort cloud consists of a large number of tiny celestial bodies, mainly composed of water ice 4, methane and other substances. The outer boundary of Oort cloud is about 654.38+ million times the distance between the sun and the earth, and it is also the edge of the influence range of solar gravity. The nearest star, proxima centauri, is twice as far away from the sun as the outer edge of Oort Cloud.

The distance between the earth and the sun is1.500 million kilometers, and it takes 8 minutes for light to travel from the sun to the earth. In order to better form images in our minds, we can reduce the physical scale of the solar system by 654.38+0 billion times. In this miniature version of the solar system, people are about the size of an atom, and the earth is only 1.3 cm, which is slightly smaller than grapes. The moon, the satellite of the earth, hangs 30 centimeters away and is the same size as grape seeds. In our miniature solar system, the sun is a fireball with a diameter of 1.5 meters, which is 50 meters away from the earth/kloc-0, and it only takes one minute to walk around. According to the distance from the sun, the earth is the third planet of the sun. From the earth to the sun, you will pass Venus, which is about the size of the earth, and Mercury, which is slightly larger than the moon. From the sun to Jupiter (about the size of a grapefruit), you need to take a bus stop (about 800 meters away). If you don't get off the bus and take another stop, you will arrive at Saturn (about the size of an apple). Uranus and Neptune are about the size of lemons, 4 and 6 stations away from the sun, respectively. Outside Neptune is the Kuiper Belt composed of small celestial bodies, and the outer edge of Oort Cloud is about 2 light years away from the sun. In our miniature solar system, it takes 20,000 kilometers to reach the Oort cloud boundary, and it takes almost 20 hours by plane. Proxima centauri, which is closest to the sun, needs to fly for 40 hours (40,000 kilometers away).

Figure 1.3 Schematic Diagram of planets of the solar system Location