Lecture 22 - The Milky Way II

Lecture 22 - The Milky Way II - The Milky Way II ASTRONOMY...

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The Milky Way II ASTRONOMY 3 Lesson 22 1 The center of the Milky Way as photographed by Axel Mellinger - see http:// canopus.physik.uni-potsdam.de/~axm/photo.cgi?Image=images/1998-02_26
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NATURE of the Universe Review of Lesson 21 Astronomy - The Milky Way II • Variable stars help us to measure distances, and to map the Milky Way. • The Milky Way has a visual diameter of 100,000 light years and contains 200 billion stars. The Sun orbits 25,000 light years from the center. • The main components of the Milky Way are the old halo with the globular cluster system, the elongated central bulge with its mixture of young and old stars, and the disk with its spiral arm structure where star formation is taking place. • The oldest stars in globular clusters are at least 13.4 billion years old. The Milky Way must have formed 13.6 billion years ago, i.e. within 100 million years after the Big Bang. Review: Milky Way I 2
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NATURE of the Universe Questions from Lesson 21 Astronomy - The Milky Way II Think about (questions from Lesson 21): • How do spiral arms form? • What is in the center of the Milky Way? 3
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• Spiral Arms (Ch. 14.5) • Mass (Ch. 14.6) • Galactic Center (Ch 14.7) NATURE of the Universe Today’s Topics Astronomy - The Milky Way II see also Lab 7 on “Structure and Motion of Spiral Galaxies” Today’s Topics: 4
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NATURE of the Universe Spiral Arms Astronomy - The Milky Way II The presence and location of the spiral arms can be derived from radio observations. Viewed from above the Milky Way would probably look like the (stretched and flipped) image of M109 shown to the right. Sun radio map visual image of M109 (a twin of the Milky Way?) 5 See http://www.noao.edu/outreach/aop/observers/m109.html and http:// antwrp.gsfc.nasa.gov/apod/ap981220.html
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NATURE of the Universe Spiral Arms Astronomy - The Milky Way II The Milky Way seems to have 4 major spiral arms, named after the constellation where most of the gas clouds making-up a spiral arm can be found. 6
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NATURE of the Universe Spiral Arms Astronomy - The Milky Way II How do spiral arms evolve with time? If the spiral arms would be a fixed pattern, their outermost edges would have to orbit the center of the Milky Way in the same amount of time as the inner-most parts (like in a Merry-Go-Round). Hence the speed would have to increase linear with distance from the center of the Milky Way. 7 Movie from “Walking L.A.” - see http://www.walkinginla.com/2005/Jun04/6_04_05.html
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Spiral Arms Astronomy - The Milky Way II Stars orbit the Milky Way on Keplerian orbits, similar to the planets in the solar system. If all the mass of the Milky Way would be concentrated in its center, stars further away from the Milky Way would have slower orbital velocities compared to stars close-in. 8
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Lecture 22 - The Milky Way II - The Milky Way II ASTRONOMY...

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