1. Chapter 25: Our Galaxy Physics of Astronomy – week 6 – May 2006

9. RR Lyrae variables Q: Why are they all about 100 L sun ? A: Horizontal branch pulsators: heating and compressing at roughly constant luminosity (T↑ and R↓)

22. The winding dilemma – if star motion caused spiral arms, structures would disappear in just a few hundred million years

23. Galactic density wave causes traffic jams in interstellar medium

28. Black hole at the center of MW Orbits of nearby stars show that SagA* has about 3.7 million M sun – very massive X-ray flares detected by Chandra last only 10 minutes, indicating a size of only 1.2 AU – very compact

30. Looking ahead Monday: no HW due, no presentations Tuesday: Bring your finished PowerPoint pages 3:00 workshop Tues: PowerPoint → Posters Thursday: bring everything to class - we’ll walk to the van together and leave at 3:00 Summary: Maxwell’s equations → speed of light “greatest synthesis …more important than the civil war”