In the infinite space, stars are concentrate in vast groups, that we call galaxy. They are billions of galaxies in the univers and each of them is compose of billions of stars and planets. Our galaxy is name the Milky Way.
Dwarfs galaxies have a size of some thousands of light-years and giants galaxies, several hundreds of thousands of light-years. They are compose of thousand of billions of stars. Galaxies are compose of gas, dusts and dark matter, bend by gravitation.
It have five kind of galaxies :
It is because of the giant telescope of the Wilson Mount (U.S.A.) who scientist had be able to take "close observation", in the years 20, what we called the Andromeda nebula: in reality, that "nebula" was a vast set of stars, situate outside our own galaxy, at some 2 millions light-years.
Since, astronomers did not stop to identify that kind of galaxies. They classify more then 200 000. But we discover always new ones. We estimate that it can be around 100 billions.
The Andromeda galaxy is relatively close to us, because the more distant, seen by humans, are at several billions of light-years.
Galaxies turn on themself and take different forms. They are different kinds : elliptics (like an egg or a globe), spirals (more or less flat, with "arms" more or less apart) and irregulars, without defenite forms.
Galaxies themselves are regroup in space. They form what we call "cluster". Then our Milky Way is part of a cluster of 19 galaxies.
Our Sun and all visible stars in the sky are part of a vast agglomeration call Milky Way galaxy. That one is compose around 1000 billions of stars, gas and dust between stars. Most of the stars in the Milky Way are in a big disk of 100 000 light-years of diameter.
The Milky Way that we can see in the sky, in the night, correspond at the plane of the disk of our Galaxy. From our position, at de 2/3 of the distance center-periphery, we can not see the center of the galaxy, to much gas and dusts can let us. In the center direction, the concentration of stars, gas and dusts are bigger. It is why the Milky Way is more bright in the Sgittarius constellation, direction of the center of the galaxy. Naturally it is in that way that we can number more nebulas and stellar clusters.
Several galaxies looking like our. Whirlpool galaxy a some degres at the south of the star locate at the end of the arm of Ursa Major. Is locate at 15 millions light-years, who is not realy far for a galaxy. so the light emit by that galaxy will take 15 millions of years to come to us.
Whirlpool galaxy, Andromeda galaxy and our Milky Way are spirals galaxies whit arms forming a spiral. Andromeda galaxy is the more close galaxy of us , and the most easier to observ.
Two small elliptics galaxies are accompagning Andromeda galaxy. Those galaxies are small but it exist also giants elliptics galaxies. With a medium openning telescope you can see several galaxies of different types.
Galaxies are so far that we can not moving enough in space to observ them in a different way. To study them, we have to observ a large number. We can see some by the edge.
Galaxies are basical cells who constitute the univers. At these days, astronomers are studying how the galaxies distribuate in space. Our galaxy, Andromeda galaxy and some two dozen of others contituing the Local Cluster, who itself is part of a cluster of galaxy more vast. The clusters of galaxies seem to be attach themself with filaments and large region of the space have no galaxies.
It is interesting to locate some galaxies with binoculars. With a small oppening telescope, you can observ more variety, but it will not be easy.
If someday you go in the equator or in south hemisphere, you will be able to observ both of those galaxies, the large and the small Magellanic clouds been see by Magellan and his crew on his trip around the world in the 16 century. You have to be at the equator or in the south of it to see them high in sky. Those galaxies wearing right their name because they seem to be light whites clouds in the sky, when we look at them at single eye. Both of those galaxies are irregulars and may have be dettach of our, the Milky Way.