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Galaxies
A galaxy is a collection of stars, planets, gas, and dust that are held together by gravitational attraction. There are categories of galaxies; including spiral, barred spiral, elliptical, and irregular. These are actually descriptions of how a galaxy looks from our earthbound point of view. This is a 2-Dimensional point of view of a 3-Dimensional object, so it can be misleading. The spiral galaxy image on the right, NGC4414, was taken by the Hubble Telescope.
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Milky Way Galaxy
We live in this spiral galaxy called the Milky Way. It is filled with stars that are forming and dying. The Milky Way is also rotating while everything within the galaxy is also in motion. This momentum is what keeps the various bodies within the galaxy separated. Astronomers estimate that the Milky Way is 100,000 light years across. Our sun is about 28,000 light years from the center. The center, or nucleus, of our galaxy is packed with stars and many unidentified objects. Some scientists believe there is a supermassive black hole at the center, while others disagree.
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Elliptical Galaxies
Elliptical galaxies have no spiral arms like the spiral galaxies above. They have less interestellar gas and dust. Very few stars form in these galaxies. One rare, giant elliptical galaxy is 20 times larger than the Milky Way, while dwarf ellipticals are more common and harder to detect. The image to the right has both spiral and elliptical galaxies.
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Irregular Galaxies
Irregular galaxies do not fit into the other categories. They do not have spiral arms or an elliptical shape. They also do not have geometric symmetry. The image on the left is a partial view of an irregular galaxy. It is called the Large Magellanic Cloud (LCM) and is the closest neighbor to the Milky Way. Astronomers estimate that it is about 180,000 light years away. Individual stars in LCM can be seen with a telescope.
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