Visions of the Universe
Visions of the Universe ISP 205
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This 10 page Study Guide was uploaded by Ms. Mckenzie Labadie on Saturday September 19, 2015. The Study Guide belongs to ISP 205 at Michigan State University taught by Eugene Brown in Fall. Since its upload, it has received 21 views. For similar materials see /class/207718/isp-205-michigan-state-university in Integrative Studies Physical at Michigan State University.
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Date Created: 09/19/15
Announcements Study Guide now available for Midterm 3 Angel Syllabus Study guide 3 next to April 3 Missouri Club 745845 tonight this room Who am 1 Jack Baldwin baldwinparnsuedu 517 3559200 x2415 Office BPS 3270 Office hours 34 M 230330 Tu 1112 Th The Milky Way Galileo rst showed that it is made up of stars Lots of Stars Clicker Question What can we conclude about the Milky Way from just the fact that we see a thin band of stars stretching across the sky It s a sphere of stars that wraps all around us It s a disk that includes the Sun It s a disk with the Sun at the center It s a disk with the Sun 23 of the way to the edge It s a disk with us looking down from the top COW P1 The Milky Way It s a disk But where are we located within that disk Mapping our Galaxy up until 1920 Lick 36 Refractor Sun near center of small universe Herschel 1784 Kapteyn early 1900 s Clicker Question Why did Herschel amp Kapz eyn get the wrong answer A The hundreds of thousands of stars in Kapteyn s sample were not enough B The method would only work for a spherical distribution of stars not for a disk They did not realize that their calculator used Reverse Polish Notation They were looking into the equivalent of a fog bank Sun near center of small universe Herschel 1784 Kapteyn early 1900 s Dust tiny grains 10 8 to 10 7 m Formed in outer layers of coolest stars Graphite silicates Built up of molecules of most common elements after hydrogen and helium Absorb light Absorb strongest in blue less in infrared The Milky Way Visible light Infrared Fullsky view Pulsatlng Varlable Stars 152 These stars regularly expand amp contract Like a big spring Change in size 9 change in temperature change in luminosity cumm vmm Slur 4 Ella moo nsv wrscz m H w Period Luminosity 1 391 39 g m Relation m m 8 S m 3 E w f A f m 1 5 E E lt1 11 Fig 1511 m Period days 9 Time days pranclmy nebula if WW 39 am 7 Fig 1210 EQWC Q heliumburning shell 39 hydrogen bummg sheu double shellv bummg core helium bumm I P quot 9 hydrogenburning shell neuummrning star core q man neuum hydrogenburning sheu subgianw led glam cove 1116 39 I igrsfzillillegslars Instablllty Stnp In populations of old stars Luminosity 9 For example Globular Clusters Occurs during He burning lO 6 4 3 T thousands degs Measuring distances inside the Galaxy 0 Parallax to 300 pc 1000 LY EWH BACKGROUND ARSquot sw t o r 1 NEAREYSTAR 1quot TH 6 MOEIETHS Period 1 Luminosity 0 Then Pulsatlng var1ables E w Relation Cepheids RR Lyraes 11 F L4n12 i Fig 1512 Fm m Period days 9 Need to correct 1500 K absorbed by dust 15000 K smr for absorption 10E the Sun 5800 K dust tot II 3000 K smr F L4m2 m h I 310K human 5 w r 10 i 0 But absorption also affects F 104 i0 wavelenglh Nu 0 Absorption or larger r 0 Dust absorbs more in blue than in red 0 Changes shape of thermal radiation curve 9 amount of absorption at each wavelength Mapping our Galaxy With globular clusters Globular Clusters offer key breakthrough in 1920 Distances from pulsating variables Spherical distribution in space Sun very far away from center The Great Debate The Size of the Universe 7 l 39 1920 quotHeiber Curtis Harlow Shapley i I Our Galaxy is rather Our Galaxy is very large small With Sun near the with Sun far from center center 300000 LY diameter 30000 LY diameten Sun 60000 LY from center Kapteyn s result 0 Based on distribution of Universe composed of gIObular clusters Pulsatmg variables many separate galax1es Spiral nebulae island Sp1ral Nebulae are 1ns1de universes our galaxy 0 Proper motion measured The Great Debate T he Size of the Universe Proper Motion Earth mm mm Velocity lS llri LYyr Shapley W 39 alaxy is very large For a measured proper motion p un far from center what sets the upper limit on the 7000 LY diameter distance 17 50000 LY from center v cannot be greater than 1 LYyr ed 0 diS Tibu39jO 0f hular clusters 39 Universe composed 01 many separate galaxies Spiralnebulae island 39Verses Rilsating Variables Spiral Nebulae are inside our galaxy Proper motion measured The Great Debate T he Size of the Universe H VEAaHeber Curtis Harlow Shapley A x Our Galaxy is rather Our Galaxy is very large small with Sun near the with Sun far from center center 300000 LY diameter 39 30000 LY diameter 39 Sun 60000 LY from center Kapteyn s result 39 Based on distribution of globular clusters Rilsating Variables Spiral Nebulae are inside our galaxy Proper motion measured Universe composed of many separate galaxies Spiralnebulae island iverses The Great Debate The Size of the Universe 7 a i 1920 3 Ci j u 1 J I zHeber Curtls Harlow Shapley i x Sun far from center Based on distribution of Universe composed of gIObular ciuSterS Pulsating var1ables many separate galaX1es Spiral nebulae island universes The Milky Way Gas large fraction of stars in thin disk 1000 LY thick Spiral structure erical halo 150 globular clusters Spherical distribution of stars Nuclear bulge 1 halo sun s locallon 1000 light years j htyears globular clusters lt ionooo lightyears gt Orbits in the Galaxy nalu sldr orbits green 100 000 LY Disk gas young fairly old stars circular orbits Bulge DiSk Bulge fairly old stars elongated orbits Halo oldest stars elongated orbits Glob Cluster
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