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The Milky Way Galaxy

Page history last edited by PBworks 13 years ago

The Milky Way Galaxy

By Jessica Yarnall




The Milky Way Galaxy, in which our solar system lies, is one of many galaxies in the universe. It is a spiral galaxy estimated to be about 13 billion years old. The Milky Way is about 80,000 to 120,000 light-years across and 7,000 light-years thick. It has between 200 to 400 billion stars. The Milky Way has three parts, the halo, the disk, and the bulge.



The halo holds the oldest stars in the Milky Way. The size of the halo is not included in the size of the Milky Way, due to the fact that it’s size is not known for sure. However, it is known that the size of the halo is the majority of the Milky Way. Its material is not visible, known as dark matter.



The disk is where the Sun and the majority of the stars lie. The disk is flattened and rotating. It contains atomic and molecular dust and gas. The disk has four major arms; the Perseus Arm, Sagittarius Arm, Centaurus Arm, and Cygnus Arm. Our solar system, however, is located in a minor arm called the Orion Spur. The arms are named for the constellations that are seen in the direction they are in.



The bulge is the center of the Milky Way Galaxy and contains dust and old stars. Because of the dust, visible light is obscured and radio and infrared observations are used to determine the structure of the bulge. It was discovered that the bulge is a very crowded place. The very center of the Milky Way is called Sagittarius A (Sag A) and is made of three sources. These sources are supernova remnant on the east side, an ionized hydrogen region on the west side, and a compact source, Sagittarius A*, at the center. Sagittarius A* is thought to be a massive black hole, 2-3 times the size of the sun.



Greek philosopher Democritus was the first person in recorded history to assume that the Milky Way existed and was made of billions of stars. In about 1918, Harlow Shapley was the first person to estimate the size of the Milky Way, as well as the Sun and Earth’s position in it. Currently, the sun is about 26,000 light-years from the center of the Milky Way and revolves around it at about 250 km/sec. The Milky Way itself moves at about 300 km/sec. Scientist estimate that in 3 billion years, the Milky Way will collide with the Andromeda Galaxy, which is coming towards it at about 30 km/sec.



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Comments (2)

gemma said

at 12:46 pm on Nov 4, 2008

this was a very good summary and breakdown of a lot of information.

Anonymous said

at 12:43 pm on Oct 14, 2008

Your web page was very descriptive. The pictures were interesting and you explained the three parts well. Even though you did it on the wrong topic, it was put together well. I thought you could have been more descriptive about the halo but other than that, it was good.

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