Answers to knowledge about the Milky Way and constellations

1. Galaxy. Galaxies are huge cluster structures composed of many stars. Most galaxies have a spiral (or vortex) structure, called a spiral galaxy. When viewed from the side, they usually have an elliptical or discus-like shape, with an obvious center and an obvious spiral. arm structure. Such as our Milky Way and the neighboring Andromeda Galaxy. The diameter of our Milky Way is about 100,000 light-years, and the Andromeda Galaxy is about twice the size of the Milky Way.

There are some that have no obvious structure, but are also clusters of a large number of stars, called irregular galaxies. Such as our Milky Way's nearest neighbors, the Large and Small Magellanic Clouds. These two galaxies are also the closest galaxies to our Milky Way. About 1.4 million light-years and 1.7 million light-years.

Galaxies also have a clustering phenomenon, that is, a varying number of galaxies gather together to form a galaxy cluster. Our Milky Way, together with the Large and Small Magellanic Clouds, the Andromeda Galaxy (about 2.4 million light-years away), and five or six other dwarf galaxies, form the Local Galaxy Cluster.

At the same time, our local galaxy cluster, together with other nearby galaxy clusters, forms the Virgo Supercluster. This is not over yet. Observations have found that super-galaxy clusters in the universe also have clustering phenomena. Numerous super-galaxy clusters form a "Great Wall of the Universe" that is hundreds of millions of light-years long. This is not over yet. In recent decades, people have discovered that the Great Wall of the Universe is also connected together. Although overall, the distribution of matter in the universe is basically uniform, most of it is concentrated in a structure similar to the Great Wall of the Universe. The universe we can currently observe is like a bunch of balloons or large bubbles squeezed together, with an empty center. On the walls of the balloons or the edges of the bubbles, connected galaxy clusters are concentrated. As shown below. Why such large-scale structures are formed is currently unknown.

The bright spots in the picture above are galaxies, each of which is on average as big as our Milky Way.

2. Constellation. Let’s talk about the celestial sphere first. Since ancient times, people have had the impression that all celestial bodies are embedded in the wall of a large ball centered on the Earth. In astronomy, this imaginary ball is called the "celestial sphere." As shown below.

The celestial sphere, redefined by astronomers, is a sphere centered on the Earth with a radius of 10 parsecs, or 32.6 light-years. All celestial bodies, no matter far or near, are projected on this sphere, and then this sphere is divided into areas of different sizes and shapes. Each area is called a constellation, and they are given different names to facilitate distinction. Such as Ursa Major - the constellation where the Big Dipper is located, Lyra, Aquila, and Orion. . . . etc. We can only say which star is in which constellation, or which galaxy is in which constellation, but we cannot say which galaxy has which constellation. The starry sky seen in other galaxies is completely different from the starry sky seen on the earth. Even in other regions of the Milky Way, the sky is completely different.

3. Nebula. There are several types of nebulae. There are planetary nebulae, as shown below, which are formed by supernova explosions when stars evolve to the end.

Sometimes, when the material spreads around during the explosion, it is not uniform, and the nebulae formed are irregular, such as the Crab Nebula in the picture below.

Some nebulae are diffuse gas clouds, usually where new stars are born, as shown below.

Some galaxies are sometimes called nebulae, such as the Andromeda Galaxy, which was formerly called the Andromeda Nebula.

Planetary nebulae and diffuse nebulae are both within the Milky Way. Nebulae in other galaxies are too far away for us to see.

Let’s see what else hasn’t been said.

The nebula is within the galaxy, so it must not be as big as the galaxy. (Not counting galaxies as nebulae). Constellations are areas in the sky, incomparable in size to galaxies and nebulae.

That’s it, it seems. Been working on it for almost an hour. That's all.