Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine [email protected] www.xanga.com/astronomy100ExamGrade DistributionScheduleExam 5 and FinalHW and PRSExamsSlide 8GradingSlide 10Slide 11OWL assignment (Due Thursday)Homework Assignment (Due May 3)What is a Galaxy?Number of GalaxiesSlide 16Slide 17We liveWhy is it called Milky Way?Slide 20Milky WaySlide 22Slide 23Slide 24Slide 25PRS questionSlide 27Our GalaxySlide 29DiskWhy are O and B stars evidence of active star formation?Slide 32Spiral ArmsSlide 34Slide 35Slide 36Slide 37Slide 38Slide 39BulgeSlide 41Slide 42Things you need to rememberBalancing ForcesRotation CurveWhat’s the problemDark MatterPossible Dark Matter CandidatesSlide 49HaloQuestionsAstronomy 100Tuesday, Thursday 2:30 - 3:45 pmTom [email protected]/astronomy100Exam•Average = 30.3/40 = 76%•Grades ranged from 0 to 40•If you guess randomly, a 0 should happen 0.013% of the time•Should happen every 7523 testsGrade Distribution•2 scores between 0 and 10•19 scores between 11 and 20•47 scores between 21 and 25•66 scores between 26 and 30•112 scores between 31 and 35•65 scores between 36 and 40Schedule•Apr 12 Tue The Milky Way •Apr 14 Thu Galaxies •Apr 19 Tue Life of a Galaxy •April 21 Thu No class•Apr 26 Tue Dark Matter •Apr 28 Thu Cosmology and the Big Bang •May 3 Tue Is there life elsewhere in the Solar System? •May 5 Thu Is there life elsewhere in the Universe? •May 10 Tue Exam 4 (material from April 12 – May 5)•May 12 Thu Exam 5 (Comprehensive)•May 20 Fri Final Exam (Comprehensive) (Optional)Exam 5 and Final•Cumulative•I will take 10 questions from Exams 1-4•No question will be exactly the same as ones on previous exams•Most questions will be very similar to those on previous examsHW and PRS•You need 20 PRS points to get 10% of your grade 100%•You need 20 HW points to get 10% of your grade 100%•We will use the PRS about twice a class•We will have about 10 more HW pointsExams•I am taking the top 4 exams out of 6 exams•If your exam average is 55% and your HW/PRS score is 100%, your average is 64%•If your exam average is 60% and your HW/PRS score is 100%, your average is 68%•If your exam average is 65% and your HW/PRS score is 100%, your average is 72%•If your exam average is 70% and your HW/PRS score is 100%, your average is 76%•If your exam average is 75% and your HW/PRS score is 100%, your average is 80%•If your exam average is 80% and your HW/PRS score is 100%, your average is 84%•If your exam average is 85% and your HW/PRS score is 100%, your average is 88%•If your exam average is 90% and your HW/PRS score is 100%, your average is 92%Grading•I want a class average at the end of the semester (top 4 exam scores, PRS, HW) to be at least 80%•If the class average at the end of the semester is less than 80%•I will multiply everybody’s average by a number that equals___________80%______________ class average at end of semesterGrading•If the class average is 80% or higher, your grade will be based on your top 4 exam scores, PRS, and HW•A 92.50 - 100•A- 89.50 – 92.49•B+ 87.50 – 89.49•B 82.50 – 87.49•B- 79.50 – 82.49•C+ 77.50 – 79.49•C 72.50 – 77.49•C- 69.50 – 72.49•D+ 67.50 – 69.49•D 62.50 – 67.49•D- 59.50 – 62.49•? below 59.49If the class average is 80% or higher,the grade distribution will besomething like thisOWL assignment (Due Thursday)•There is be an OWL assignment due on Thursday April 14 at 11:59 pm.•There are 15 questions and a perfect score will give you 2 homework points.Homework Assignment(Due May 3)•Make up a test question for next test•Multiple Choice•A-E possible answers•1 point for handing it in•1 point for me using it on test•The question needs to be on material that will be on the 3rd exam•15 people got extra HW credit for me using their question (or inspiring a question)What is a Galaxy?•A Galaxy is a huge collection of stars that are bound together by gravityNumber of Galaxies•There are thought to be 80 billion galaxies in the observable universeWe live•We live in the Milky Way Galaxy•Thought to be 13.6 ± 0.8 billion years oldWhy is it called Milky Way?•It looked like a flowing ribbon of Milk to the GreeksMilky Way•Contains between 200 and 400 billion stars•Diameter is 100 thousand light years acrossPRS question•What two elements are the two largest constituents of the Milky Way Galaxy?–A) Helium and Carbon–B) Helium and Oxygen–C) Hydrogen and Iron–D) Carbon and Iron–E) Hydrogen and HeliumPRS question•What two elements are the two largest constituents of the Milky Way Galaxy?–A) Helium and Carbon–B) Helium and Oxygen–C) Hydrogen and Iron–D) Carbon and Iron–E) Hydrogen and HeliumOur Galaxy•There is a disk part•And Spherical Part –Bulge and HaloDisk•The disk includes all of the material (gas, dust, stars, and star clusters) which are confined to the plane of rotation of the galaxy•Contains lots of gas and dust and is therefore the site of active star formation•Lots of blue stars (O and B stars)Why are O and B stars evidence of active star formation?•A) Because they tend to be massive•B) Because they tend to be older•C) Because they tend to be younger•D) Because they tend to be less massive•E) Because they tend to be coolerWhy are O and B stars evidence of active star formation?•A) Because they tend to be massive•B) Because they tend to be older•C) Because they tend to be younger•D) Because they tend to be less massive•E) Because they tend to be coolerSpiral Arms•6 spiral armsSpiral Arms•Can’t be fixed patterns of stars •Stars nearer the center would complete an orbit much quicker than stars farther out•Would cause the arms to wrap up into a tight coil•We do not see that among spiral galaxiesSpiral Arms•Spiral Arms are actively forming new stars•In spiral arms, see clusters of young, bright, blue stars•In spiral arms, we also see lots of gas and dust•Between the arms, you see old, red starsBulge•The bulge is at the center of the galaxy, is a flattened spheroid •This is a high density region where red stars predominate, which are very old and about 10 billion years old•There is growing evidence for a very massive black hole at