PHY122 Ch12 Slides

PHY122 Ch12 Slides - The Milky Way Almost everything we see...

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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. From outside, our Milky Way might very much look like our cosmic neighbor, the Andromeda Galaxy.
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Southern sky Milky Way in binoculars on Dec. 9, 1985 showing also Halley’s comet.
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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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First Studies of the Galaxy First attempts to unveil the structure of the galaxy by Thomas Wright (1750) and 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 ~33,000 ly 6,500ly circa 1900
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Actual Structure of the Milky Way 1. Disk with spiral arms 2. 75000 ly in diameter 3. Sun is 2/3 from center 4. Halo of gas, dust, & dark matter within and surrounding Milky Way 5. Nuclear bulge with high density of stars 6. Gobular clusters of stars above & below disk, orbiting nucleus 75,000 ly There are both disk and spherical components that have different ages.
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Spiral Arms Spiral arms are slowly orbiting shock waves, i.e., densified regions of gas and dust. New stars tend to form in spiral arms.
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Clusters of Stars in the Milky Way Galaxy Two types of clusters of stars : 1) Open clusters = young clusters of recently formed stars; within the disk of the galaxy. 2) Globular clusters = dense clusters of old stars; mostly in the halo around the galaxy. How do we know the ages??
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Orbital Motions in the Milky Way Disk stars : Nearly circular orbits in the disk of the galaxy Halo stars : Highly elliptical orbits; randomly oriented.
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PHY122 Ch12 Slides - The Milky Way Almost everything we see...

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