Galaxy: In the vast universe and ocean, there are various "islands" dotted with countless stars and various celestial bodies, which are called galaxies in astronomy. The earth where we live is in a huge galaxy-the Milky Way. In the universe outside the Milky Way, there are hundreds of millions of space giant islands similar to the Milky Way, collectively known as extragalactic galaxies. Cluster: Among the numerous stars in the Milky Way, there are many stars gathered together, not only in the form of single star, but also in the form of double stars or multiple stars. A cluster with more than 10 stars is called a cluster. What binds these stars together is gravity. There are thousands of members in the cluster. They can be divided into open clusters and globular clusters. There are clusters everywhere in the Milky Way, but the types of clusters are different in different places. Nebula: Nebula is a cloud-like celestial body composed of gas and dust in interstellar space. The density of matter in the nebula is very low. If measured by the standards on earth, some places are almost vacuum. However, the size of the nebula is very large, often reaching tens of light years in Fiona Fang. Therefore, nebulae are generally much heavier than the sun. Nebulae have various shapes. Some nebulae are irregular in shape, diffuse and have no clear boundaries, which are called diffuse nebulae; Some galaxies evolved from dying stars like the sun into red giant stars, and the outer gas flowed out and surrounded its debris, forming beautiful planetary nebulae.
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Cluster: Stars are usually distributed in groups. Generally speaking, we call a cluster with more than ten stars and interconnected in physical properties "cluster". Such as the Pleiades in Taurus and Pisces in Cancer. A cluster is a group of stars with more than 10 stars and their physical relationship (gravity). A cluster with loose structure and irregular shape composed of dozens to thousands of stars is called an open cluster. They are mainly distributed on the galactic plane, so they are also called Galactic Clusters, which are mainly composed of blue giant, such as the Pleiades Cluster (also known as the Pleiades Cluster). Tens of thousands to hundreds of thousands of stars are like a circle as a whole, and clusters with dense centers are called globular clusters. Cluster [1] is a group of stars that are gathered together and bound by gravity due to physical reasons. The spatial density of its member stars is obviously higher than that of the surrounding star fields. Cluster is divided into two types according to its shape and the number of member stars: open cluster and globular cluster. Usually, the number in the corresponding directory is used to name the cluster. The most commonly used is Messier catalog, abbreviated as "M". It only includes brighter clusters.
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Constellation: Constellation refers to the stars in the sky. In fact, the stars in the same constellation have no actual relationship with each other, but their projection positions on the celestial sphere are similar. Since ancient times, people have been interested in the arrangement and shape of stars, and naturally linked some stars with similar positions to form constellations. Constellations are divided into Polaris, South Star and Zodiac. The whole day is currently divided into 88 constellations. Constellations are generally named after musical instruments or Greek mythical figures. Constellations play an important role in astronomy; Astrology also uses images of the zodiac 12, but astronomers regard astrology as pseudoscience without using real scientific methods. Basically, dividing stars into constellations is a random process. Different civilizations have different constellations made up of different stars-although some constellations made up of more conspicuous stars are roughly the same in different civilizations, such as Orion and Scorpio. The International Astronomical Union divides the sky into 88 official constellations with precise boundaries, so that every star in the sky belongs to a specific constellation. Most of these official constellations are based on the ancient Greek traditional constellations handed down from the Middle Ages. In order to identify the stars easily, people divided several regions according to their natural distribution in the sky. Different sizes. Each region is called a constellation. Connect the bright stars in the same constellation with lines to form various figures. In shape, they are similar to animals and utensils.
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Galaxy: The word galaxy comes from the Greek Galaxis (γ α λ α ξ? α? ), in a broad sense, can be an operating system composed of countless star systems (including the stars themselves, of course) and dust (such as nebulae). Referring to our Milky Way, it is a huge system containing stars, interstellar gas, cosmic dust and dark matter, and bound by gravity. Typical galaxies, from dwarf galaxies with tens of millions (10) stars to elliptical galaxies with trillions (10) stars, all revolve around the center of mass. Except for individual stars and thin interstellar matter, most galaxies have a large number of multi-star systems, clusters and various nebulae. Star system, or galaxy, is an "island" of giant stars in the universe, and it is also one of the largest and most beautiful celestial systems in the universe. So far, people have observed about 1000 billion galaxies in the universe. Some are close to us, and their structures can be clearly observed; Some galaxies are very far away, and the farthest known galaxies are close to15 billion light years.
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Nebula: [Nebula] One of many giant celestial bodies composed of very thin gas or dust in the interstellar space of our Milky Way or other galaxies. It looks like a cloud-like celestial body. All non-stellar gas and dust clouds in the Milky Way and outside the solar system. Sun Li introduced Lu Xiu Wanji Guo Ru's Happy Parting: "Life is like a nebula in space, which is seamless, ever-changing, interrelated and mutually causal." He Jingzhi's collection of songs Dongfeng Wan Li: "The nebula of the infinite universe is sending us constant echoes." Ai Qing's Ode to Light: "Everyone is a life, and man is a speck in the galactic nebula."
Nebulae contain almost all expandable objects except planets and comets. Their main component is hydrogen, followed by nitrogen, and they also contain a certain proportion of metallic elements and nonmetallic elements. In recent years, it has also been found to contain organic molecules and other substances. Nebula is a cloud-like celestial body composed of gas and dust in interstellar space. The density of matter in the nebula is very low, and some places are vacuum if measured by the standards on earth. However, this nebula is very huge, often reaching dozens of light years in Fiona Fang. Therefore, nebulae are generally much heavier than the sun. Nebulae have various shapes. Nebulae are related to stars. The gas thrown by the star will become a part of the nebula, and the nebula material will be compressed into a star under the action of gravity. Under certain conditions, nebulae and stars can be transformed into each other. At first, all cloud-like objects in the universe were called nebulae. Later, with the development of astronomical telescope and the continuous improvement of people's observation level, the original nebula is divided into three types: cluster, galaxy and nebula. When we talk about space, we often think that there is nothing there, but a dark and silent vacuum. Actually, this is not entirely right. The vast space between stars may be silent, but it is far from a real "vacuum", but there are all kinds of substances. These substances include interstellar gas, dust and particle flow. People call them "interstellar matter". Interstellar matter is closely related to the evolution of celestial bodies. Observations have confirmed that interstellar gas is mainly composed of hydrogen and helium, which is the same as that of stars. In fact, stars are "condensed" by interstellar gas. Interstellar dust is a small solid substance, which is composed of carbon compounds, oxides and so on. The distribution of interstellar matter in space is not uniform. Under the action of gravity, gas and dust in some places may attract each other, become dense and form clouds. People vividly call them "nebulae". According to the morphology, the nebulae in the Milky Way can be divided into diffuse nebulae and planetary nebulae. Compared with stars, nebulae have the characteristics of large mass, large volume and low density. The mass of an ordinary nebula is at least equivalent to thousands of suns, and the radius is about 10 light-year. Nebulae are usually named according to their positions or shapes, such as Orion Nebula and Lyra Nebula.
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Galaxy: The Galaxy was also called Tianhe, Han Yin and Xinghe in ancient China. It is a faint luminous band across the starry sky. The Milky Way intersects the celestial equator of Aquila and is located in the northern hemisphere. The milky way draws a band with different widths on the celestial sphere, which is called the silver band. Its widest point is 30, and its narrowest point is only 4 ~ 5, with an average of about 20. This is just a part of the galaxy. The Milky Way occupies a very important position in China culture, and there is a famous legend "Meet at the Queqiao Bridge". A broad, shiny and irregular band of light extends completely around the celestial sphere and looks like a river. The Milky Way can only be seen on a clear night. It is caused by the light of countless dark stars (stars). The Milky Way is not the Milky Way, but a part of it. A bright band that can be seen on the earth when projected into the sky. You can refer to the "Galaxy" entry to distinguish the two.
The beautiful Milky Way [1] is also called "Tianhe" and "Tianhan" among China people. It looks like a bright white belt, cutting the whole sky from northeast to southwest. There are many small spots in the Milky Way, just like scattered white powder, which are reflected into one piece. In fact, white powder is a huge star, and the Milky Way is made up of many stars. The sun is one of the stars. There are more than 200 billion stars like the sun in the Milky Way, and many stars have satellites. Looking down at the Milky Way from space, the Milky Way looks like a whirlpool. In the clear night sky, when you look up at the sky, you can not only see countless shining stars, but also a faint scarf-like light belt across the whole sky, just like a big river in the sky, which runs north-south in summer and close to east-west in winter, that is the Milky Way. In the past, because science was underdeveloped, we didn't know what it was, so we named it Tianhe. Therefore, there are many beautiful fairy tales in our country, such as the Cowherd and the Weaver Girl who meet at Queqiao on Tanabata every year. In fact, the Milky Way is a part of the Milky Way and belongs to the solar system. It is named because the bright band whose main part is projected on the celestial sphere is called the Milky Way in China. It is the round face full of stars that we see when we look at the Milky Way from the inside. Because the light emitted by the star is far away from us, it is large in quantity and mixed with interstellar dust gas, so it looks like a band of light shrouded in smoke, which is very beautiful. The brightness of each part of a galaxy is different. The direction of Centauri near the silver heart is brighter than other parts.
Encyclopedia of star clusters: /view/6248.htm
Constellation encyclopedia: /view/5 186.htm
Encyclopedia of Galaxies: /view/885 1.htm
Encyclopedia of nebula: /view/8606.htm
Galaxy encyclopedia: /view/8250.htm