Stars and galaxies
All the stars we can see from Earth form a record structure called Galaxy. This set of stars has incredible dimensions. The diameter of the disc is 100,000 light years and its thickness in the center is 15,000 light years. (The year of light is about 10 billion kilometers.) The sun and the planets around it (including Earth) are part of this Galaxy and can be said to be on the edge of the disk.
From Earth, heaven has a different way of looking to one side or another. If we look perpendicularly at the plane of the disk of the Galaxy, we will see few stars, but on the contrary, if we look in the direction of the plane of the Galaxy, numerous stars will appear to us, although at first glance it is difficult to see several stars. We will see the whitish strip, the Milky Way (cross section of our Galaxy).
The galaxy consists of stars and gases. These gases form nebulae, from which the new stars emerge. On the contrary, gas can be a residue of dead stars.
Stars can be individual or in groups. Stars are sometimes in pairs, but they are also sets of thousands of stars.
The galaxy is not a perfect disk and around a sphere similar to that of the nucleus the stars and nebulae are divided into spiral arms that unite in the center.
However, our Galaxy is not the only one in the Universe. There are millions of galaxies and each will have about 100 million stars. Some are spiral-shaped, but are also elliptical, circular and irregular. Magellanic clouds, for example, are irregular.
In turn, galaxies are united forming sets of tens or hundreds. With existing resources at present, we can study existing galaxies up to 14 billion light years from us, but these limits are expected to be exceeded shortly.
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