As an area that they have been very interested in since childhood, Hua Feng and Yun Meng have been immersed in the study of astronomy for the next ten days.

Extragalactic galaxies:

In Copernicus's theory, it is impossible that a star is just a point of light in the sky of the outermost star.

In 1584, Giordano Bruno proposed that the stars were distant suns.

In the first half of the 18th century, Bruno's speculation was increasingly accepted by E. Halley about the development of stars on their own and J. Bradley's scientific estimates of the distant distances of stars.

In the mid-18th century, T. Wright, I. Kant, and J. H. Lambert speculated that the stars and the Milky Way that spread throughout the sky constituted a vast celestial system. Friedrich Wilhelm Herschel pioneered the method of sampling statistics, using a telescope to count the number of stars in a large number of selected areas of the sky and the ratio of bright stars to dark stars, and in 1785 he first obtained a flat and flat, uneven outline, and the sun centered on the structure of the Milky Way, laying the foundation for the concept of the Milky Way.

In the following century and a half, H. Shapley discovered that the sun is not at the center of the Milky Way, J. H. Oort discovered the rotation and spiral arms of the Milky Way, and many people determined the diameter and thickness of the Milky Way, and the scientific concept of the Milky Way was finally established.

In the middle of the 18th century, Kant and others also proposed that there are countless celestial systems like the Milky Way in the entire universe.

By 1924, E.P. Hubble had confirmed the existence of extragalactic galaxies by measuring the distance of the Andromeda galaxy using the Cepheid parallax method.

Diameter and age of the universe:

The latest research suggests that the diameter of the universe can be 93 billion light-years or more.

The current observable age of the universe is about 13.82 billion years.

The current theory of the universe, which suggests that the universe may be a saddle-like negative curved shape, stems from the Big Bang theory, in which the entire universe is shaped like a balloon blown up, and we live on the "surface" of the universe.

Stephen Hawking says that the shape of our universe may be an incredible geometric shape, closer to surrealist art, like the figure created by the Dutch artist Moritz Cornelius Escher.

Hawking's idea is based on string theory, which is still hypothetical and has not yet been tested. If we use words to describe the shape of the universe, it should be the whole presents a multi-mosaic pattern, with infinitely repeated distorted surfaces, and the curved surfaces are interlocking, just like the "Circular Limit IV" pattern created by Cornelius Escher, which is also similar to that of the American engineer P.H. Smith's "Smith Circle" is similar in that it embodies the concept of hyperbolic space, a non-Euclidean geometric form of space.

Hierarchy:

Contemporary astronomical research results show that the universe is a hierarchical and expanding celestial system with diverse material forms and constant motion and development.

Planets, asteroids, comets, and meteoroids all orbit around the central celestial body, the Sun, making up the solar system.

There are other planetary systems outside the solar system as well. About 250 billion sun-like stars and interstellar matter make up the Milky Way, a much larger celestial system. The Milky Way is about 100,000 light-years in diameter, and the Sun is located in one of the spiral arms of the Milky Way, about 26,000 light-years from the galactic center.

There are many similar celestial systems outside the Milky Way, called extragalactic galaxies, often referred to simply as galaxies. With 100 billion galaxies currently observed, scientists estimate that there are at least 2 trillion galaxies in the universe.

Galaxies are clustered into large and small groups, called galaxy clusters. On average, each galaxy cluster has about 100 galaxies with a diameter of tens of millions of light-years. Tens of thousands of galaxy clusters have been discovered. A small cluster of about 40 galaxies, including the Milky Way, is called the Local Group.

A higher-level celestial system formed by several galaxy clusters clustered together is called a supercluster. Superclusters tend to have an elongated shape, with diameters of hundreds of millions of light-years. Usually superclusters contain only a few clusters of galaxies, and only a few superclusters have dozens of clusters.

The supercluster of galaxies formed by the local group of galaxies and about 50 nearby clusters is called the local supercluster.

Galaxy Classification:

According to the sequence number that can reflect the development state of galaxies, galaxies can be roughly divided into five types: elliptical galaxies, lens galaxies, spiral galaxies, barred spiral galaxies and irregular galaxies.

Among the celestial bodies of the solar system: the mass of the sun accounts for 99.86% of the total mass of the solar system, and it firmly attracts all the celestial bodies in the solar system around it with its strong gravitational pull, so that they rotate around itself in an orderly and orderly manner. At the same time, the Sun, as an ordinary star, leads its members to move around the center of the Milky Way for eternity.

The radius of the Sun is 696,000 km, the mass is 1.989×10^30kg, and the core temperature is about 15000000 °C.

If a person were to stand on the surface of the sun, he would weigh 20 times as much as he would on Earth.

Based on observational data and theoretical calculations, the modern nebula hypothesis proposes that the primordial nebula of the solar system is a small cloud of massive interstellar cloud disintegration, which rotates at the beginning and contracts under its own gravitational force, and the central part forms the sun, and the outer part evolves into a nebula disk, and the nebula disk forms a planet after the nebula disk. At present, there are different schools of thought in the modern nebula theory, and there are still many differences between these schools, which need to be further studied and confirmed.

Venus is the second planet from the Sun and is second only to the Moon in brightness in the night sky.

There is no water on Venus, there is a severe lack of oxygen in the atmosphere, carbon dioxide accounts for more than 97%, there is a layer of concentrated sulfuric acid clouds in the air that is 20 to 30 kilometers thick, and the ground temperature never falls below 400 °C. The atmospheric pressure on the surface of Venus is 90 times that of the Earth, which is equivalent to the pressure in the Earth's oceans at a depth of 900 meters.

Venus's atmosphere is mainly composed of greenhouse gases such as carbon dioxide, and the runaway greenhouse effect is the main cause of Venus's extreme climate. Since Venus does not have the intrinsic magnetosphere protection, the huge energy released by the magnetic field reconnection in the magnetosphere is induced, which causes the atmosphere of Venus to escape at an accelerated rate after being heated. The scientific community believes that the escape of the atmosphere on Venus is the cause of the lack of water on Venus and the dense atmosphere rich in carbon dioxide, which leads to a severe greenhouse effect.

Jupiter is the fifth planet from the Sun and the largest, with a combined mass of 2 times greater than all other planets (318 times that of Earth) and a diameter of 142,987 km. It is a gaseous planet with no physical surface, consisting of a ratio of 90% hydrogen to 10% helium atoms, 75/25% mass ratio) and trace amounts of methane, water, ammonia, and "stones". This is very similar to the composition of the primordial solar system nebulae that formed the entire solar system.

Jupiter may have a stony core equivalent to 10-15 Earth's masses. On the inner core, most of the planetary material is concentrated, in the form of liquid hydrogen.

Liquid metallic hydrogen is made up of ionized protons and electrons (similar to the interior of the sun, but much cooler). Jupiter has a total of 67 Europa.

From the center of Jupiter in descending order: Calliste, Callisto, Callisto, Callisto, Europa, Callisto, Europa, Callisto, and Callisto.

Mercury is the closest planet to the Sun. With a radius of about 2,440 kilometers, Mercury is the smallest of the eight planets. Mercury has a huge temperature difference between day and night, with 430 degrees Celsius during the day and about -170 degrees Celsius at night, making it the planet with the largest temperature difference among the eight planets in the solar system. [37] Mercury's outer atmosphere is very thin and is made up of atoms and ions on Mercury's surface and in the solar wind. [38] Scientists have confirmed that the surface of Mercury is rich in carbon, which is believed to be responsible for the black color of Mercury's surface, and that the rocks on Mercury's surface are made of graphitic carbon with a low weight percentage.

Mars is Earth's closest neighbor and is the fourth planet in the solar system from the inside out. It has a diameter of 6794km, a volume of 15% of the earth, and a mass of 11% of the earth. The surface of Mars is a desolate world, with 95% carbon dioxide in the air. The Martian atmosphere is so thin that it is less than 1% of Earth's atmosphere, so it can't conserve heat at all. As a result, the surface temperature of Mars is extremely low, rarely exceeding 0°C, and at night, the lowest temperature can reach -123°C.

Mars is known as the red planet because its surface is covered with oxides, giving it a rusty red color. Much of its surface is a large desert with large amounts of red oxides, as well as ochre-colored gravel fields and solidified lava flows. Mars is often characterized by violent winds, which can create very large dust storms that can cover the entire planet of Mars. Dust storms can last for several weeks at a time. The ice caps at the poles of Mars and the Martian atmosphere contain water. Probe data obtained from the surface of Mars prove that in ancient times, there was liquid water on Mars, and the volume was particularly large.

Saturn is the sixth planet from the Sun, with a diameter of 120,536 km, second only to Jupiter in size. Composed mainly of hydrogen, with small amounts of helium and trace elements, the inner core consists of rock and ice, and the outer perimeter is surrounded by several layers of metallic hydrogen and gas. Earth is 1.3 billion kilometers away from Saturn.

Saturn's gravitational pull is 2.5 times stronger than that of the Earth, and it can pull other planets in the solar system, keeping the Earth in an elliptical orbit and keeping an appropriate distance from the Sun for life to flourish. When Saturn's orbit is tilted 20 degrees, it will bring the Earth's orbit closer to the Sun than Venus's, and at the same time, it will cause Mars to leave the solar system completely.

Saturn is the only known planet that is less dense than water, and if you could fit it into a huge bath, it would be able to float. Saturn has a huge magnetosphere and a wind-swept atmosphere, with winds reaching speeds of up to 1,800 km/h near the equator. Of the 31 moons orbiting Saturn, Titan is the largest, larger than Mercury and the Moon, and the only moon in the solar system with a thick atmosphere.