The Galaxy, it is the name of our galaxy, it is an enormous spiral wheel of stars, a diameter of 100 000 light years. What appears of the Earth, it is a white continuous band of the Milky Way. This galaxy really consists of three spiral arms (The arm Sagittarius, the arm of Orion and the arm Perseus). The mass of our Galaxy is of 2x1041 kg or 1011 solar masses. Numerous indications suggest that the center of numerous galaxies is occupied by a black hole. A galaxy is thus an assembly of stars, interstellar matter and probably big quantities of dark matter, the cohesion of which is assured by the strengths of gravitation, and the mass of which is of an order of height superior to hundred million solar masses. The Big and the Small Cloud of Magellan are nearby galaxies of ours, visible in the southern latitudes. They are with the Milky Way and Andromeda, the only visible galaxies in the bare eye.

The Galaxies interact with their neighbors, and these interactions modify their shape. Two galaxies can even merge. The galaxies are three main morphological types: elliptic, spiral, irregular. As stars, which are grouped together in galaxies, most of the galaxies are also bound between them by the strength of gravitation. A structure containing until about fifty galaxies is a group of galaxies. A structure containing several thousand galaxies grouped in a sector of some mega parsecs is a heap of galaxies. The groups and the heap of galaxies are grouped together in super heap, huge collections themselves containing tens of thousand galaxies. On a very large scale, the distribution of the heap of galaxies is not uniform, but not organized in patches or in strands.
The spatial telescope Hubble sends regularly images showing us all the variety of the galaxies.

Our Galaxy is of type spiral quite as the galaxy M83 above.

The galaxies were born 3 in 4 billion years after Big Bang. It is the gravity which transformed diffuse clouds of hydrogen and helium, in embryos of galaxies. These embryos collapsed under the influence of their own gravity. This collapse compressed and warmed the gaseous matter, transforming it into hundreds of billion small gaseous balls, of some million degrees, called <stars>. When all the gaseous matter metamorphosed into stars, these galaxies become then elliptic; 30 % of the galaxies are elliptic. They prevail in the heart of the heap. Others succeed in transforming into stars, that 4/5 of the gaseous mass, the fifth

remainder flattens in a thin disk, continuing to be converted in stars but much more slowly and rather, along the spiral arms which are outlined there. It is the spiral galaxies which dominate the galactic world, 60 % of the galaxies are spiral. One find them especially, in the peripheral galactic regions of the heap. Others set much more time to convert the gaseous matter in stars, because they are dwarfs, they contain only some billion stars, having no special shape, they are baptized by <irregular galaxies>.

10 % of the galaxies are irregular.

The galaxy of the Triangle, also known under the name of M33, is a spiral galaxy of type Sc, situated in the constellation of the Triangle. The galaxy M33 NGC 598 the third of the local Group in ascending order, after the Milky Way and Andromeda. This galaxy is small compared with its neighbor, the galaxy of Andromeda M31, and with our Milky Way, but in the average of the spiral galaxies of the universe. M33 approaches us in 182 km/sec according to R. Brent Tully, or in 179 +/-3 km/sec according to the Ned. It is situated in 3 million years light.

This galaxy was probably discovered before 1654 by Hodierna, follower of Galilee, who maybe grouped it with the opened heap NGC 752. It was independently rediscovered on August 25th, 1764 by Charles Messier who cataloged it as M33. Classified by William Herschel September 11th, 1784 under the name H V.17, the galaxy of the Triangle was one of the first spiral nebulas identified as some by William Parsons.

Galaxy of the Sombrero M 104 NGC 4594 in the heap Virgo. This brilliant galaxy owes this name of Sombrero to its appearance. According De Vaucouleurs, we see it since just 6 degrees in the South of the equatorial plan, realized by a thick dark band of opaque dust. This characteristic was probably the William Herschel's first discovery with its big telescope.

Opposite, the dissimilar image of 3 photos taken by the camera FORS1 of the VLT Antu (European telescope of 8,2 m of the ESO based in Chile). It was obtained after an exposure of 6:20 am on January 30th, 2000.

Its mass is only 1/5 of that of our Galaxy but its diameter is 80 000 light years. The spiral arms contain many young stars or still in formation. M74 is the most brilliant constituent of a heap of galaxies which includes besides: NGC 660, UGC on 1171, UGC on 1175, UGC on 1176, UGC on 1195 and UGC on 1200.