Ch 12 (The Milky Way Galaxy)

Ch 12 (The Milky Way Galaxy) - Chapter 12 The Milky Way...

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The Milky Way Galaxy Chapter 12:
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We will answer these questions 1. How do we know we live in a galaxy? 2. How did our galaxy form and evolve? 3. What are the spiral arms? 4. What lies at the very center of our galaxy?
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The Milky Way Almost everything we see in the night sky belongs to the Milky Way. We see most of the Milky Way as a faint band of light across the sky.
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From outside, our Milky Way might very much look like our cosmic neighbor, the Andromeda Galaxy. The Milky Way
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12-1 The Discovery of the Galaxy Our galaxy is wheel shaped – only a wheel could produce the band of the Milky Way in the sky The Herschel’s: First to attempt to map the stars in the galaxy – early 1800’s Concluded that the sun was near the center of the galaxy Astronomers still believed this at the beginning of the 20 th century
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First Studies of the Galaxy First attempt to unveil the structure of the galaxy by William Herschel (1785), based on optical observations. The shape of the Milky Way was believed to resemble a grindstone, with the sun close to the center
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Strategies to explore the structure of our Milky Way I. Select bright objects that you can see throughout the Milky Way and trace their directions and distances. II. Observe objects at wavelengths other than visible (to circumvent the problem of optical obscuration), and catalog their directions and distances. III. Trace the orbital velocities of objects in different directions relative to our position.
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Determining the Structure of the Milky Way Galactic Plane Galactic Center The structure of our Milky Way is hard to determine because: 1) We are inside. 2) Distance measurements are difficult. 3) Our view towards the center is obscured by gas and dust.
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The Size of the Milky Way Harlow Shapley (1885-1972) noticed that different kinds of star clusters have different distributions in the sky. There are two kinds of star clusters – open clusters and globular clusters . Open clusters are concentrated along the Milky Way and globular clusters are scattered all over the sky. Shapley noticed that globular clusters were strongly concentrated toward the constellations Sagittarius & Scorpius .
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Exploring the Galaxy Using Clusters of Stars Two types of clusters of stars: 1) Open clusters = young clusters of recently formed stars; within the disk of the Galaxy 2) Globular clusters = old, centrally concentrated clusters of stars; mostly in a halo around the galaxy Globular Cluster M 19 Open clusters η and χ Persei
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Globular Clusters Dense clusters of 50,000 – a million stars Old (~ 11 billion years), lower-main-sequence stars Approx. 200 globular clusters in our Milky Way Globular Cluster M80
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“controlled” by the combined gravitational field of the entire galaxy.
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This note was uploaded on 11/08/2011 for the course AS 101 taught by Professor Biegel during the Fall '11 term at Montgomery College.

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Ch 12 (The Milky Way Galaxy) - Chapter 12 The Milky Way...

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