1. Variable Stars: Stepping Stones To The Universe Albert Holm Computer Sciences Corporation & Space Telescope Science Institute, Retired STScI Public Lecture Series April 4, 2011

2. Fireflies?

3. No, RR Lyrae-type variable stars Copyright J. Hartmann, Harvard U., and K. Stanek, Ohio State U.

4. RR Lyrae-Type Variable Stars Discovered by Williamina Fleming in 1893 in Omega Centauri

5. RR Lyrae-Type Variable Stars Change their brightness by pulsing like the air in a pipe organ Discovered by Williamina Fleming in 1893 in Omega Centauri

6. RR Lyrae-Type Variable Stars Change their brightness by pulsing like the air in a pipe organ About 40 times brighter than the sun Discovered by Williamina Fleming in 1893 in Omega Centauri

7. Pop Quiz RR Lyrae stars are interesting because they… 1.Are fun to watch change from hour to hour, even minute to minute 2.Provide clues about what happens in the interior of stars 3.Provide clues about how stars age 4.Help determine the size and shape of the Milky Way galaxy 5.All of the above

8. How can we use a candle?

9. To determine distances

13. The big sisters of RR-Lyrae stars are … RR Lyrae Our Sun

14. The big sisters of RR-Lyrae stars are Cepheid variables RR Lyrae Our Sun Delta Cephei

15. Delta Cephei, the prototype Cepheid Variable

16. John Goodricke

17. Cepheid Variables: Measuring the Universe Henrietta Leavitt

18. Cepheid Variables: Measuring the Universe Henrietta Leavitt

19. Cepheid Variables: Measuring the Universe Henrietta Leavitt

20. Cepheids – Key to Edwin Hubble’s Discoveries

21. Cepheid Variables: Measuring the Universe

22. The Expansion and Age of the Universe

23. We can identify variable stars by how the light we see from them changes with time 1.Stars that vary in brightness 2.Time scales of seconds, hours, days, years or centuries

24. How to make a light curve

29. Light Curves … Fingerprints of Variable Stars

37. Astronomers don’t have time to look at the sky!

38. The Solution: People who love to look at the sky!

40. Why Are Amateur Astronomers’ Observations Crucial for HST Science? A scientist has requested observations of an object that could become so bright that it could damage the Instrument

41. Why Are Amateur Astronomers’ Observations Crucial for HST Science? A scientist has requested observations of an object that could become so bright that it could damage the Instrument Operations staff insert commands to cancel the observation automatically unless overridden

42. Why Are Amateur Astronomers’ Observations Crucial for HST Science? A scientist has requested observations of an object that could become so bright that it could damage the Instrument Operations staff insert commands to cancel the observation automatically unless overridden Amateur astronomers determine whether the object is safe to observe

43. Why Are Amateur Astronomers’ Observations Crucial for HST Science? A scientist has requested observations of an object that could become so bright that it could damage the Instrument Operations staff insert commands to cancel the observation automatically unless overridden Amateur astronomers determine whether the object is safe to observe Operations staff bypass the fail safe commands

44. What was V455 Andromedae doing when Dr. Szkody wanted to observe it?

45. What might V455 Andromedae have been doing?

46. Another way that amateurs enable scientists to get data Provide alerts when something interesting occurs

47. Dwarf Nova Model

48. Another way that amateurs enable scientists to get data Dr. Peter Wheatley’s observations of SS Cygni

49. People who love to look at the sky! The American Association of Variable Star Observers www.aavso.org

50. People who love to look at the sky! The American Association of Variable Star Observers www.aavso.org

51. People who love to look at the sky! The American Association of Variable Star Observers www.aavso.org

52. American Association of Variable Star Observers AAVSO 100 years old this year!

53. 1918 Photo of AAVSO

54. Edward C. Pickering

55. 1918 Photo of AAVSO Anne S. Young

56. www.aavso.org

57. 20,000,000 observations freely available! www.aavso.org

58. And there are short essays telling about many of these stars and why they are interesting www.aavso.org

59. Eclipsing Variables Eclipsing variables are not intrinsically variable The change in brightness is due to a line of sight effect

60. A mysterious eclipsing binary

62. What’s the answer? Here’s one idea

63. Epsilon Aurigae

64. Stay tuned for the next discoveries be announced about Epsilon Aurigae

65. Moving on to Supernovae The Ultimate Variable Stars

66. Is the expansion of our universe speeding up?!!!

67. Contents of the Universe - 72% dark energy - 23% dark matter - 5% ordinary matter

68. Our substance comes from Supernovae

73. Iron Calcium Gold Uranium

74. Thank you, variable stars!