There are many galaxies in the Universe. Our galaxy has two close neighbouring galaxies- the Large and Small Magellanic Clouds-which are a twentieth and a hundredth the size of the Milky Way. Also closely neighbouring our galaxy is the Andromeda Galaxy, and there are more galaxies that exist a little further out. Together, this group of galaxies form what is known as the Local Group. Throughout the Universe, there are many galaxies, embedded in larger agglomerations or cluster composed of thousands of individual galaxies. Closest to our Galaxy is the Virgo Cluster, which is situated about 50 million light years away. The Virgo Galaxy is so large that its gravitational force is sucking the Milky Way in towards it. Situated about 300 million light years away is the Coma Cluster, which is made up 10,000 galaxies.
Andromeda has a spiral shape and it is very similar to our Galaxy. Most of the galaxies that are observed have a spiral shape and extend to great lengths. They tend to be found in low-density regions of space, where there are few other galaxies.
Besides spiral galaxies, there are elliptical galaxies. Elliptical galaxies are large accumulations of stars with no obvious features. They do, as their name indicates, have an elliptical shape, and they are classified by their ellipticity. When naming elliptical galaxy, the convention is to indicate it with a E followed by a number. For example, if an elliptical galaxy is E0, it will not be elliptical, but it will be spherical. If it is classified as E1, the galaxy will be slightly elliptical. An E8 galaxy will be basically flat and look unlike a spiral.
Edwin Hubble developed a classification system for the galaxies. In his system, galaxies are ordered into a tuning fork structure. At the base of the tuning fork, are the E0s. As we move farther down the fork’s stem, the galaxies’ shapes become more elliptical, until the end of the tuning fork where they become essentially flat without spiral arms. This is where the two prongs of the fork begin. As you move down the prongs, the prongs become larger and larger, and the galaxies become larger with longer arms. On one prong, galaxies have spherical bulges, and on the other arm, galaxies have cores shaped as bars.
Most of the galaxies that are observed are classified under this classification scheme. Galaxies that are not classified are not because their shape is too irregular, or do not possess spiral arms. Galaxies that have an irregular shape are called irregulars, where all the other galaxies that cannot be classified are placed. Many irregular galaxies are a result of a collision between spiral and elliptical galaxies. Most irregular galaxies, such as the Magellanic Clouds, contain up to a third of their masses in gas, which is used to form stars.
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