1. ASTR 1102-002 2008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture19]

2. Chapter 23: Our Galaxy and Chapter 24: Galaxies

5. Schematic Illustration of Our (Milky Way) Galaxy

9. Real ‘All Sky’ Images of Our (Milky Way) Galaxy

18. Aside: Atomic transition that gives rise to 21-cm radiation, which is used by astronomers to map out the distribution of neutral hydrogen throughout our Galaxy (and other galaxies), is also the physical principle underlying the MRI (magnetic resonance imaging) diagnostic tool in modern medicine.

19. Medical MRI

20. Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is ~ 50 kpc (as illustrated in following slide) Herschel’s map of our Galaxy (1785) based on star counts –Thin disk not much more than 1 kpc across –Sun approximately at center of disk

21. Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is ~ 50 kpc (as illustrated in following slide) Herschel’s map of our Galaxy (1785) based on star counts –Thin disk not much more than 1 kpc across –Sun approximately at center of disk

23. Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is ~ 50 kpc (as illustrated in following slide) For example, Herschel’s map of our Galaxy (1785) based on star counts … –Thin disk not much more than 1 kpc across –Sun approximately at center of disk

24. Herschel’s Map of MW Galaxy

25. Determining Size of MW Galaxy We have not always known that the diameter of our Galaxy is ~ 50 kpc (as illustrated in following slide) For example, Herschel’s map of our Galaxy (1785) based on star counts … –Thin disk not much more than 1 kpc across –Sun approximately at center of disk Herschel’s map grossly distorted by interstellar extinction

26. Prominent and Obscured Objects

27. Shapley’s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun’s location Distances to GCs obtained using RR Lyrae variable stars as “standard candles”

28. Shapley’s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun’s location Distances to GCs obtained using RR Lyrae variable stars as “standard candles”

30. Shapley’s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun’s location Distances to GCs obtained using RR Lyrae variable stars as “standard candles”

31. Shapley’s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun’s location Distances to GCs obtained using RR Lyrae variable stars as “standard candles”

33. Determining Distances in Astronomy Stellar parallax Spectroscopic parallax (main-sequence fitting): –Remember distance modulus: (m – M) = 5 log(d) – 5 –If you know “M” for a certain type of star, then a measurement of “m” gives you “d” Standard candles: Identifiable stars for which you know “M”

34. Determining Distances in Astronomy Stellar parallax Spectroscopic parallax (main-sequence fitting): –Remember distance modulus: (m – M) = 5 log(d) – 5 –If you know “M” for a certain type of star, then a measurement of “m” gives you “d” Standard candles: Identifiable stars for which you know “M”

35. Determining Distances in Astronomy Stellar parallax Spectroscopic parallax (main-sequence fitting): –Remember distance modulus: (m – M) = 5 log(d) – 5 –If you know “M” for a certain type of star, then a measurement of “m” gives you “d” Standard candles: Identifiable stars for which you know “M”

36. Determining Distances in Astronomy Stellar parallax Spectroscopic parallax (main-sequence fitting): –Remember distance modulus: (m – M) = 5 log(d) – 5 –If you know “M” for a certain type of star, then a measurement of “m” gives you “d” Standard candles: Identifiable stars for which you know “M”

37. Determining Distances in Astronomy Stellar parallax Spectroscopic parallax (main-sequence fitting): –Remember distance modulus: (m – M) = 5 log(d) – 5 –If you know “M” for a certain type of star, then a measurement of “m” gives you “d” Standard candles: Identifiable stars for which you know “M”

38. Determining Distances in Astronomy Stellar parallax Spectroscopic parallax (main-sequence fitting): –Remember distance modulus: (m – M) = 5 log(d) – 5 –If you know “M” for a certain type of star, then a measurement of “m” gives you “d” Standard candles: Identifiable stars for which you know “M”

39. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

40. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

41. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

43. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

44. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

45. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

46. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

48. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

49. NOTE: Transient Events (in time) also occur

52. Example Standard Candles RR Lyrae variables –Pulsation period of about ½ day –Luminosity is 100 x solar luminosity Sun: M = +4.8; let’s call it M = +5 for simplicity RR Lyrae: M = 0 “Population I” Cepheid variables –Luminosities range up to 10,000 solar (M = - 5) –(Pulsation) period-luminosity correlation Type Ia supernovae –Luminosity 3 x 10 9 solar !

53. Distance Ladder

54. Shapley’s View of MW Galaxy Look out of the plane of the MW disk to minimize obscuration due to interstellar extinction Distribution of Globular Clusters not symmetric about Sun’s location Distances to GCs obtained using RR Lyrae variable stars as “standard candles”

56. Stellar Populations Pop I Pop II Pop III

59. Prominent and Obscured Objects