The universe is boundless and the stars are scattered. How do astronomers determine regions and constellations?

The stars in the constellation refer to the luminous stars that can be observed by the naked eye on the earth (maybe very close and the brightness is very weak). It may also be a long distance and bright brightness). On the same celestial sphere, stars that are close to each other and visible to the naked eye form a constellation (in fact, the stars in the constellation are far away from each other, and some even exceed the width of the Milky Way). But on earth, it is very close to the naked eye. Astronomers classify such stars as constellations. A * * * has only a few constellations. According to the observed geographical latitude and longitude, the observed time and the observed celestial sphere area. You can tell by looking at it, and then by looking at the shape. There are so many stars in the real sense that they are unimaginable and as many as sand. But more than 99.99% are invisible to the naked eye, and these are not counted in the constellation.