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Chapter 16 The Milky Way Galaxy 16.1 Overview n How many stars are in the Milky Way? – About 200 billion n How many galaxies are there? – billions.

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Presentation on theme: "Chapter 16 The Milky Way Galaxy 16.1 Overview n How many stars are in the Milky Way? – About 200 billion n How many galaxies are there? – billions."— Presentation transcript:

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2 Chapter 16 The Milky Way Galaxy

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5 16.1 Overview n How many stars are in the Milky Way? – About 200 billion n How many galaxies are there? – billions and billions n How old is the Milky Way Galaxy? – It is 15 billion years old and will remain active for a another 10 billion years. n Are all stars members of the Milky Way Galaxy?

6 What are some of the major features of our galaxy? n Disk n Nuclear Bulge n Halo n Spiral Arms n Sun n Globular Clusters n Open Clusters and Nebula

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9 Where in the Milky Way is our solar system located? n The solar system is located in a spiral arm about 28,000 light years from the center of the Milky Way.

10 How do we know that we are located in the spiral arm? n In 1917 Harlow Shapley discovered that the globular clusters form a huge spherical system that is not centered on the Earth.

11 Finding Our Place Sun Early view Sun at center Harlow Shapley Globular Clusters evenly distributed Globular Clusters unevenly distributed

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14 Zone of Avoidance n a band running around the sky in which few galaxies are visible n caused by dust within the Milky Way Galaxy

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16 16.2 Differential Galactic Rotation n Material closer to the galactic center orbits with a shorter period than the material farther from the galactic center.

17 16.2.1 Rotation and Mass Distribution n To the chalk board...

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19 Chapter 17 Normal Galaxies

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22 The Great Debate Harlow Shapley Heber Curtis April 26, 1920 A galaxy is an island universes! A galaxy is a nebula with the Milky Way!

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24 M104 M81 M51

25 Spiral Galaxies n galaxies like the Milky Way with arcing structures lying in a plane and emanating from the nuclear bulge

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27 M32 - E2 M87 - E1 NGC 4125

28 Elliptical Galaxies n galaxies with an elliptical shape, no spiral arms, and little interstellar matter

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30 NGC 1097 NGC 4477 M91 NGC 4123

31 Barred Spiral Galaxies n galaxies with a bar of stars running through the nuclear bulge

32 Hubble Classification of Galaxies n Ellipticals – From E0 (round) to E7 (oblate) n Spirals – SO have nuclei but no spiral arms – From Sa (large nuclei and tight arms) to Sc (small nuclei and the most open arms) n Barred Spirals – From SBa to SBc

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34 M87 Centaurus A

35 Irregular Galaxies n galaxies that are asymmetrical and are sometimes just two or more galaxies colliding

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37 Galactic Collisions

38 Chapter 18 Clusters of Galaxies

39 Edwin Hubble

40 Galaxy Observations n During the 1920's Edwin Hubble and Milton Humason photographed the spectra of many galaxies with the 100 inch telescope at Mount Wilson. n They found that most of the spectra contained absorption lines with a large redshift.

41 Red Shift and Distance 24 Mpc1200 km/s 300 Mpc15,000 km/s 780 Mpc39,000 km/s 1220 Mpc61,000 km/s

42 Galaxy Observations n Using the Doppler effect, Hubble calculated the velocity at which each galaxy is receding from us. n Using the period and brightness of Cepheid variables in distant galaxies, Hubble estimated to distances to each of the galaxies.

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44 Hubble’s Law n Hubble noticed that there was a linear relationship between the recessional velocity and the distance to the galaxies. n This relationship is know as Hubble’s Law: v = H o d recessional velocity = Hubble’s Constant  Distance

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46 Hubble’s Law n H o is known as the Hubble constant and is about 75km/s/Mpc. n This means that a galaxy that is 1 megaparsec from Earth will be moving away from us at a speed of 75km/s.

47 Edwin Hubble

48 Cosmology n The study of the origin, structure and evolution of the universe. n What does the Hubble law tells us about our universe? Our universe is expanding.

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50 Raisin Cake Model Like raisins in rising raisin cake, galaxies move away away from each other in our expanding universe.

51 Cosmology n Hubble Time n The age of the universe if the expansion has been constant. n t = 1/H o = ? n The expanding universe probably originated in an explosion called the Big Bang between 12 and 18 billion years ago.

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53 Cosmology n Will the universe end? – Present observations suggest that it will expand forever. n What caused the Big Bang? n Where did the energy come from? n Why did it happen? Unknown…

54 Chapter 19 Active Galaxies and Quasars

55 Structure of Our Universe n Universe - all space – Galaxies and Quasars n Virgo Cluster of Galaxies n Milky Way Galaxy n Local Star Cluster n Our Solar System n The Earth


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