What is the definition of constellation? Can it compare with galaxies?

Do you still compare constellations with galaxies?

Constellation is only artificially divided from the perspective, and it is an area of the celestial sphere. Let's make an analogy. If you sit on the top of the mountain, we can regard the top of the mountain as the earth at this time. There are villages around the mountain. We can divide the villages seen from different directions into village A, village B, village C and village D. At this time, we can see that there is a giant tree (giant tree star) and an iron tower (iron tower star) in village A, and other villages have different scenery. If we stop looking at this mountain and go to another mountain, does it feel that Village A is different? Galaxies actually exist, and constellations are shapes produced by projection on the celestial sphere, so the comparison between constellations and galaxies in size is meaningless.

Compared with galaxies, constellations are more emotional. Constellations are divided according to the gathering patterns of stars that can be observed in the night sky, and the division is based on vision rather than real star positions. Therefore, the stars in the same constellation often come from different galaxies, and are artificially divided into constellations when they reach the earth from different positions in the universe with visible light.

Constellations have no distance. Constellations just look at the sky from the earth and artificially divide the sky into regions. All celestial bodies located in this area belong to this constellation, no matter how far or near. Therefore, even in the same constellation, the distance between each star is different, some are closer, some are farther, and some two stars seem to be close, but in fact they may be far apart. Of course, all the stars that can be seen from the earth are in the Milky Way.

Because the 88 constellation includes all the sky except the earth, it includes all the space centered on the earth. But the total number of stars in the Milky Way galaxy may be as high as 200 billion. Even with the largest telescope, you can't see so many stars. There are not only stars in the constellation, but also extragalactic galaxies, such as Andromeda galaxy, Magellanic galaxy and so on. These galaxies are not in the Milky Way, but other galaxies outside the Milky Way. If the telescope is powerful enough, you can see almost countless galaxies in a constellation.

The division of constellations artificially regards the celestial sphere as a plane to divide the easily recognizable areas, and the distances between the stars contained in each constellation are different. Each constellation has its own deep space objects, and it can even be said that almost every constellation contains extragalactic galaxies, but humans are temporarily unable to observe them.