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During most of our history, humans could only observe galaxies as diffuse spots in the night sky. However, today we know are huge clusters of stars and other materials.

In fact, our solar system is part of a galaxy, the only one we've seen from within: The Milky Way. We've always known but of course in ancient nobody knew what it was. It appears as a whitish band across the sky and, hence, itsname: Milk Road.

Within the Milky Way can find various formations of stars and interstellar dust. The most noteworthy are the nebulae and star clusters. Presumably that also exist in other galaxies.
Galaxies in the Universe: Galaxies are huge collections of stars, gas and dust. In the universe there are hundreds of billions ... [+]
Galaxies classes: When large telescope, in most galaxiesonly the mixed light is detected from all ... [+]
Active galaxies: Almost all galaxies have a black hole at its center. While the black hole is active, traps and engulfs all ... [+]
Nearby Galaxies: The nearest galaxies to the Milky Way are those belonging to the Local Group. Are easily seen with a telescope ... [+]
The Local Group: Nearby galaxies are attracted by its gravity effect and aregrouped into clusters. Smaller clusters are called groups ... [+]
The Milky Way: On clear nights you can see a white stripe across the sky from side to side, with many stars. They are only a small ... [+]
What is the Milky Way?: If we could see the Milky Way from the outside, we would see the bulging center, bright yellow, shaped ... [+]
Star clusters: The stars do not appear in isolation, but ingroups we call "clusters". A star cluster is a group ... [+]
Nebulae: nebulae are structures of interstellar gas and dust. As more or less dense, visible or not from Earth ... [+]
Types nebulae: One of the most notable aspects of the nebulae is its variety of forms and structures. Thanks to modern telescopes and ... [+]
What is an emission nebula: nebulae are clouds of gas and dust where starsare born ... [+]
What is a dark nebula: In cold areas of the Cosmos, where the interstellar gas and dust are abundant, the material is concentrated and ... [+]
Distant galaxies: The farthest galaxies are more than 13,000 million light years away, almost at the edge of the visible universe ... [+]
Galaxy clusters: Clusters of galaxies are gigantic structures in the Universe. The galaxies emitgravity lot ... [+]
Astronomical catalogs: The catalogs are lists of astronomical deep sky objects that occupy a fixed position in the sky ... [+]

For many years known nebulous objects between stars which are believed were part of the galaxy, some had spiral and hence be denominated spiral nebulae. The use of more powerful telescopes with better resolving power enabled astronomers Hubble andMilton Humason comedown in the decade of the 30 established the presence of Cepheid variable stars in the Andromeda spiral nebula, stating that this was a separate galaxy to ours and Located more than 1,000,000 million light years (the distance has been measured at 2.9 million light years), confirmed that Emmanuel Kant's theory of the existence of island universes.

All galaxies are systems of largenumber of stars, interstellar matter and dark matter, most of them are evidence of the existence of super massive objects at its center (black holes). The distances between galaxies are so large they are measured using the mega parsec is a million parsecs (about 3.3 million light years). The nearest galaxy to the Milky Way (no satellite of it) is the Andromeda which is mega parsecs 0899.
Types ofGalaxies
In 1936 Edwin Hubble divided galaxies into different types: ellipticals, spirals, barred spirals and irregulars. This system also sought to classify, determine an evolution path starting as ellipticals and spirals changing then finally to irregular. Spiral galaxies could be regular spirals or barred spirals. In the first group arms arising directly from the center and the second seem...