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Our Galaxy the Milky Way

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Our Galaxy the Milky Way Our Galaxy The Milky Way Orin Harris and Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Spring 2021 c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 1 / 93 Overview The Milky Way ISM Nebula Galactic Recycling Evolution The Galactic Center Review c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 2 / 93 M31: The Andromeda Galaxy NGC 4565: The Needle Galaxy SA(s)b Andromeda NGC 4565 The Milky Way The Night Sky The Night Sky Etymology Moments in History Q: Galactic Fog Milky Way M13 The Milky Way Q: Disk Thickness Q: Disk Diameter Q: Galactic Halo Milky Way Orbits Galactic Merry-Go-Round Fig 14.02 Q: Bobbing Stars Galactic Mass from Orbital Velocity Q: Orbital Speed Q: Sun’s Orbit Milky Way Spiral Arms Spiral Arm – Theory c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future slide 5 / 93 c Matipon Tangmatitham Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) in Maui Etymology • The English word galaxy is derived from the greek γαλαξιας (galaxias) meaning milky. • The English Milky Way is derived from from Latin Via Lactea from the Greek γαλαξιας κυκλoς´ aka Milky Circle. c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 93 Moments in History • Galileo Galilei first resolved the band of light known as the Milky Way into individual stars with his telescope in 1610, demonstrating the hypothesis of Anaxagoras and Democritus (5th century BCE). • Galactocentrism: 1785 William Herschel: Sun at center of flattened disk. (His view through the disk was obstructed by the “fog” of interstellar medium) • 1918 Harlow Shapley: globular clusters centered on a point 50,000 ly 27,000 ly from us. • Heber Curtis (1917) & Edwin Hubble (1920) demonstrated that spiral “nebulae” were actually distant galaxies beyond the Milky Way. c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 9 / 93 Q: Galactic Fog How does the interstellar medium affect our view of most of the galaxy? A) It prevents us from seeing most of the galactic disk with visible and ultraviolet light. B) It absorbs all wavelengths of light. C) It produces so much visible light that it blocks our view of anything beyond it. D) It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or X-rays. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 10 / 93 The Milky Way (SBc)b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Halo b b b b b b ∼ 150 Globular Clusters b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Bulge b b b b b b b b b b Sgr A* b b b b b b b b b b b b b b b b b Sun b 27,000 ly from galactic center Disk b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b 12 200 billion stars, 100, 000 ly diameter, 1, 000 ly thick, M & 10 M⊙ Globular Cluster: M13 (NGC 6205) Q: Disk Thickness What is the thickness of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 93 Q: Disk Thickness What is the thickness of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 93 Q: Disk Diameter What is the diameter of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 93 Q: Disk Diameter What is the diameter of the Milky Way’s disk? A) 100 light years B) 1,000 light years C) 10,000 light years D) 100,000 light years E) 1,000,000 light years c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 93 Q: Galactic Halo What kinds of objects lie in the halo of our galaxy? A) open clusters B) hot, young blue giants C) globular clusters D) gas and dust E) all of the above c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 93 Dark Matter Halo b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Orbits b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b 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