1. Announcement... Extra Credit! See a planetarium show at Museum of the Rockies:  Sky Quest  Current Sky  Not a laser show or a kid’s show! Sign in at the front desk. Free admission! 20 points — same as an activity! One time only. By the last day of classes!

2. Announcement... Extra Credit! Taylor Planetarium current schedule:

3. Developing a model of the solar system Review: Spherical Earth Motion of the stars Motion of the Sun & Moon Solar System: Geocentric models  Aristotle  Ptolemy Copernicus

4. Models of the solar system Stars move each night Sun moves through the stars throughout the year Planets  move slowly through the stars  planet means “wandering star” Earth-centered or Sun-centered

5. Aristotle’s model (384-322 BC)

6. Problem: retrograde motion Planets sometimes back up! Aristotle’s model doesn’t do that.

7. Retrograde motion of Mars http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

8. Retrograde motion of Mars

20. Cladius Ptolemy (85-165) Earth is at the center Earth is imperfect, celestial sphere is perfect Circles govern heavenly motions

21. Ptolemy’s geocentric model

22. Retrograde motion (Ptolemy) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

23. Retrograde motion (Ptolemy)

39. Epicycle Ptolemy’s model was actually even more complicated.

40. Copernicus’ heliocentric model Ptolemy’s model was used for almost 1400 years. Copernicus proposed a very different model in 1543:  Planets, including Earth, move around Sun.  Retrograde motion is explained without epicycles.

41. Retrograde motion

42. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

43. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

44. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

45. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

46. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

47. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

48. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

49. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

50. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

51. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

52. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

53. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

54. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

55. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

56. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

57. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

58. Retrograde motion (Copernicus) http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html

59. In class writing: Discuss some examples of questions science can answer and some questions science cannot answer How are the latter questions answered? If you lived in the year 1543, which would you believe: Copernicus’ model (Sun- centered) or Ptolemy’s model (Earth-centered)? Why?

60. Do you use WebCT? A. Yes, I love it B. Yes, but I don’t love it C. No D. No, I hate it E. What’s WebCT?

61. Team activity #12 Don’t forget your team # Skip “tracing orbits” in part II, but do question 3.