To the Stars and Beyond

1. To the Stars and Beyond University of Wisconsin – Eau Claire Continuing Education Dr. Nathan Miller Department of Physics & Astronomy WELCOME BACK!

2. Main topics of Course • Appearance and motions of night sky objects • Visit to the planetarium to see sky motions in 3D (we will walk over together) • Telescopes: design and basic use • The Lives of the Stars • The Universe and the Big Bang • Life in the universe and planets where it may be found

3. The Stars

5. How bright?How big?How massive?How hot?How old?What are they made of?What causes them to shine?How far away?

6. First Question: How Bright? • Hipparchus – 2nd cent. BC. Put many stars in 6 brightness categories • 1st magnitude = brightest • 6th magnitude = dimmest seen

7. Magnitude 5 star is 100 times dimmer than Magnitude 1 star • Sun = Mag -26 • Brightest star = Mag -1 • Dimmest star you can see = Mag 6 • Amateur Telescope = Mag 12 • Hubble Space Telescope = Mag 25

8. But raw brightness doesn’t tell you much about stars themselves. i.e. A 100-watt bulb held next to your eye appears much brighter than a street light. But which is the more powerful bulb?  You need the distance

9. To find Distance, use Parallax

10. Parallaxes are small. • A star with a parallax of 1 arcsecond would be at a distance of 1 parsec (=“parallax second”) • No stars are this close

11. Absolute magnitude:How bright would the star be if it were at 10 parsecs?

12. A star with a brighter absolute magnitude is really putting out more light than a star with a dimmer absolute magnitude.

13. Apparent Brightness • Absolute Brightness (“luminosity”,”Absolute magnitude”) • Distance • Give me any two and I will tell you the third

16. To study color better, use a prisim to spread out starlight into colors

17. Star’s colors are caused by “blackbody radiation” • http://phet.colorado.edu/en/simulation/blackbody-spectrum

23. The Hertsprung-Russell Diagram- The Rosetta Stone for StellarAstrophysics

24. What Russell needed to know (1913): Spectral types of the nearest stars (Spectra) Distance of nearest stars (Parallax) Brightness of nearest stars (photography) Use Distance and Brightness to get Intrinsic luminosity

25. The basic Hertsprung Russel Diagram:

26. Plotted on the graph, most stars are on the Main Sequence

27. Every square meter of a hot thing emits much more light that a square meter of a cold thing

28. So the main sequence stars are all roughly the same size.

29. All the nearest stars plotted:

30. Some stars do not fall on the Main Sequence: Giants and White Dwarfs

31. If something is hot but dim, it must not have many square meters  small • If something is cool but bright, it must have many square meters  huge

32. So we can find the sizes of stars:

33. Draw lines of equal radius on the HR diagram:

34. Which of the directions in the following HR diagram correspond to an object which is contracting? • A. A. • B. B. • C. C. • D. D. • E. More than one of the above

36. Star Clusters • 2 kinds – • Open Clusters – young, in galactic plane • Globular Clusters – old, swarm around galaxy

38. Pleiades Open Cluster

39. Open Cluster Near Galaxy Center

40. Open Cluster M38

41. Globular Cluster M2

42. Globular Cluster M15

43. Clusters and Stellar Evolution In each cluster: • Stars all made at nearly same time • Stars all the same distance from Earth • Stars in cluster that look brighter really are brighter

45. Zero-Age Main Sequence (ZAMS) –Position on HR diagram where stars begin H fusion in core

46. Core slowly depletes H fuelcore shrinks  core heats up  higher fusion rate  star gets slightly brighter

49. Cluster Main Seq.Turnoff • Bright, high mass stars evolve first • In older clusters, these stars have started to “turn off” the main sequence