Where is Earth in the Milky Way?

https://phys.org/news/2016-07-earth-milky.html

The article posted to phys.org called, “Where is Earth in the Milky Way?”, relates to our 15th objective, “I can describe the structure and size of the Milky Way Galaxy” sufficiently. To begin, the article goes into detail of the size of the Milky Way. It is stated that the size of the Milky Way is enormous, measuring about 100,000-120,000 light years in diameter and about 1,000 light years thick with up to 400 billion stars located in it. Also going off of this information, the Milky Way is about 9,500-11,400 quadrillion km in diameter. Consuming other galaxies in the past and continuing to do so still today, such as the Sagittarius Dwarf Galaxy, is how our Milky Way has made its current shap and size. Another galaxy that has contributed to the size of our Milky Way is the Canis Major Dwarf Galaxy because it is the closest other galaxy next to the Milky Way, which allows its stars to constantly be added to the Milky Way’s disk. With how large our galaxy is, it is surprisingly enough only a middle-weight galaxy when it is compared to other galaxys in the local Universe. The article also informs us on the structure of the Milky Way. It is stated that if a person was to travel outside of the galaxy and look down at it, they would see that our Milky Way is a spiral galaxy. New information has revealed that instead of the galaxy being known for having four spiral arms, newer surveys have determined that it actually seems to have only two called “Scutum-Centaurus and Carina-Sagittarius”. These arms are formed from density waves that orbit the galaxy, consisting of stars and clouds of gas that are clustered together. These density waves move through the area, compressing the gas and dust, which leads to periods of active star formation in the region. With this matter, it is also stated that all of this makes up about 10-15% of all of the luminous matter that is visiable, along with all of the stars.  As stated before, our galaxy is about 100,000 light years across, and about only 6,000 light-years into the disk in the visable spectrum is what we can see. Accounting for 90% of the Milky Way’s mass is the surrounding of the vast halo of dark matter. The article also informs that when light pollution is not significant, the dusty ring of the Milky Way can be recognized in the night sky sometimes. From our lectures in class, we learned that the Milky Way is a large galaxy, but that several smaller galaxies orbit it, as well as disk stars orbiting the center of the galaxy. Although, according to our lecture tutorial while viewing the figure of the Milky Way and charts of surrounding stars and galaxies, we learned that these stars were all inside of the Milky Way and that the local group galaxies were all outside of it. I found this objective to be very informative of material that i was once not aware of. Of course i knew of our Milky Way, but never knew the details of the structure and size of it. I found this article, as well as the objective, to be interesting and informing at the same time and am glad to say i can now describe the features of our own Milky Way.

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