From Ptolemy to Copernicus, as early as the 4th century BC, the ancient Greek philosopher Aristotle had put forward "geocentric theory", that is, the earth was located at the center of the universe. In A.D. 140, Ptolemy, an ancient Greek astronomer, published his masterpiece Astronomy 13, and systematically established the geocentric theory on the basis of summarizing the previous work. According to this theory, the earth is spherical, at the center of the universe, motionless, and other celestial bodies revolve around the earth. This theory clearly explains the phenomenon that the sun, the moon and the stars rise in the east and set in the west every day, and conforms to the religious doctrine that God created human beings and the earth must occupy the supreme position in the universe, so it has been circulated for more than 1300 years.
As early as 2000 years ago, the ancient Greek astronomer Aristak put forward a simple "Heliocentrism". He pointed out that the sun is stationary in the center of the universe, while the earth revolves around the sun and rotates around its axis. Unfortunately, due to the limitation of scientific level, this genius's thought has not been recognized by people. It was not until the end of the Middle Ages that people began to doubt the correctness of the geocentric theory, because the positions of planets calculated by Ptolemy geocentric theory were inconsistent with the actual astronomical observations. 1543, Copernicus, a Polish astronomer, put forward Heliocentrism systematically in his immortal masterpiece On the Movement of Celestial Bodies. In his Heliocentrism system, the sun is the center of the universe, and the earth and other planets move around the sun in circular orbits. In this way, the complicated work of explaining planetary motion phenomena with extremely complicated motion images in Ptolemaic geocentric system suddenly becomes very simple. Later, the German astronomer Kepler pointed out that the orbit of the planet around the sun should be an ellipse rather than a circle, and the sun is located at a focus of the ellipse. This significant development enables the observation results to be explained and predicted by theory, and Heliocentrism's position is further consolidated.
According to Heliocentrism, as far as people on the earth are concerned, the positions of the stars in the sky should change with the movement of the earth around the sun. In the nearly 300 years after Copernicus put forward Heliocentrism, people made a lot of observations, trying to prove this point, but never succeeded. It turns out that the stars are far away from the earth, and the nearest one is as far as 43 trillion kilometers. Therefore, the position change of this constant star caused by the revolution of the earth around the sun is only 12.5. The farther away from the star, the smaller the change, and the observation instruments at that time could not detect it. It was not until 1838 that German astronomer Bessel first measured the position change of a constant star named Swan 6 1 and calculated its distance as 1 1.2 light years, thus finally confirming Copernicus' Heliocentrism. The status of the earth has been reduced from a special celestial body living in the universe to an ordinary planet orbiting the sun. The sun is not in the center of the universe 1608. The Dutchman Liporsay accidentally invented the telescope. The following year, Italian physicist and astronomer Galileo made the first astronomical telescope himself immediately after learning the news, and constantly improved it. Galileo discovered craters, phases of Venus, moons of Jupiter and sunspots on the surface of the moon with his telescope, and found that the vast Milky Way is made up of countless stars.
As early as the middle of15th century, Archbishop Nicholas of Germany had speculated that the stars in the night sky were very distant suns. 1584, Italian Bruno clearly pointed out that the universe is infinite, the stars are the distant sun, and the sun is just an ordinary member of countless stars. 1750, British astronomer Wright pointed out that the Milky Way and all the observed stars constitute a huge flat celestial system. Because the sun and the earth are located in this system, we can only see the Milky Way and scattered stars from different directions. 1785, British German astronomer William? 6? 1 Herschel used his homemade 46 cm telescope, which was the largest telescope in the world at that time. Through long-term practical observation and careful analysis, he established the first model of the galaxy. In this model, the sun is still at the center of the Milky Way, which was then called the universe. Because of Herschel's personal prestige at that time, this concept has been maintained for 130 years.
The name "star" means "star" in China and western Europe. Because for a long time, people found that the position between stars is fixed, so they took such a name. 17 18, the British astronomer Harley pointed out for the first time that the concept of star immobility was wrong through observation and analysis. Later, Herschel correctly realized that the star motion we observed was the result of the combination of the star's own motion and the solar space motion. 1783, he found that the sun was moving in the direction of Vega at a speed of about 20 kilometers per second through statistical analysis of a large number of observed star movements. The discovery of solar space movement completely shook Copernicus and Heliocentrism's view that the sun is fixed.
19 17, American astronomer shapley confirmed that the sun is not located in the center of the Milky Way, but relatively close to the edge of the Milky Way, thus correcting the error of Herschel's model of the Milky Way. In this way, the position of the sun has also changed, from a special star in the center of the Milky Way to an ordinary star without a special position in the Milky Way, and the position of the earth in the universe is even less special. Does the Milky Way already contain all the contents of the universe?
Long before Herschel tried to determine the structure of the Milky Way, people had observed some faint and fuzzy cloud-like objects in the sky besides stars, and named them "nebulae". For example, in 16 12, German astronomer Marius first discovered the Andromeda nebula with a telescope. 1750, Wright cleverly guessed that some of these nebulae might be giant star systems similar to the Milky Way. 1755, the German Kant clearly pointed out for the first time that there are countless similar celestial systems in the outer space of the Milky Way, called extragalactic galaxies, or simply galaxies, and even the Andromeda Nebula is a good example. However, at that time, people lacked understanding of the fine structure of the nebula, let alone the distance, so they could not make a judgment.
Although after Herschel's era, observation methods have been improved and physics research methods have been involved in astronomy, until the beginning of the 20th century, there was still no clear conclusion about the nature of nebulae. In the debate on the topic of "the scale of the universe" held by American Academy of Sciences 1920 in April, one party headed by Curtis thought that some nebulae were actually extragalactic galaxies, while the other party represented by shapley insisted on opposing it. This is the famous "Shapley-Curtis dispute" in the history of astronomy. In the debate, the opposing views of both sides were deadlocked and it was difficult to tell the winner. The key to the problem is to accurately measure the distance of the nebula.
Astronomers have been making unremitting efforts to determine the distance between different celestial bodies. In addition to triangulation, various photometry methods have been developed to determine the distance between celestial bodies, one of which is to use a variable star with special photometry characteristics-Cepheid variable star. It turns out that the variation of Cepheid's luminosity is very regular. The greater the luminosity, the longer the light variation period. Therefore, as long as the light variation period of Cepheid variable is measured, its actual luminosity can be calculated, and then its distance can be calculated by comparing the actual luminosity with the observed luminosity. This calculation is quite accurate, so Cepheid variable stars are called "celestial ruler". At the beginning of the 20th century, Mount Wilson Observatory in the United States built the 2.5m astronomical telescope with the largest caliber in the world at that time. 19231010.6, American astronomer Hubble used this telescope to take pictures of the Andromeda nebula, in which the outer edge of the nebula has been decomposed into stars. Hubble discovered many such variable stars. Using these Cepheid variables, Hubble calculated that the distance of Andromeda Nebula is 2.25 million light years, far beyond the scope of the Milky Way. The existence of extragalactic galaxies was finally confirmed, and Andromeda Nebula should be renamed Andromeda Nebula. A long-running scientific debate has finally come to an end.
Herschel's work expanded people's horizons to the Milky Way, and Hubble's discovery further brought people from the star world to the galaxy world, and human understanding of the universe took a step forward. There is nothing special about our earth in the universe. The earth was not deliberately arranged by God, and human beings were naturally not created by God. However, it is on such a planet that human beings have interpreted a glorious history of civilization and finally got a correct understanding of the general situation of the universe.