1. 1

2. Light Pollution Stellar Evolution 2

3. Lab Notes • Be sure you have started your “report” lab. • Constellation presentations next week. • Observatory field trips… 3

4. Night Lights • http://apod.nasa.gov/apod/ap101104.html 4

5. Limiting Magnitude and Light Pollution 5

6. Limiting Magnitude • Limiting Magnitude is a measure of the dimmest star visible from a given location. • Center of a big city: ~2.0 • Suburbs: ~4.5 • Downtown Durango: ~5.5 • La Plata County (FLC observatory): ~6.5 • Depends on observer experience • Depends on local glare • Depend on how dark adapted your eyes are. You should wait 20-30 minutes to measure this. 6

7. Limiting Magnitude • Use stars of known magnitude (e.g. Little Dipper) 7

8. Limiting Magnitude • Count the stars in a well-defined region • Chose one of the predefined star regions that is overhead • Count the number of stars visible within the region boundary • Look up the number on the published tables to find the corresponding limiting magnitude 8

9. Limiting Magnitude 9

10. Limiting Magnitude Alpha-Epsilon-Beta Gem stars LM 1 1.2 2 2.4 3 3.2 4 3.9 5 4.3 6 5.0 7 5.1 8 5.3 9 5.6 10 5.7 11 5.9 12 6.1 13 6.2 14 6.3 15 6.4 16 6.5 18 6.6 20 6.7 22 6.9 23 7.0 25 7.2 30 7.5 10

11. How many Stars Can You See? Magnitude Range Cumulative Stars % Increase Seen -1-1.50 to -0.51 2 - 0-0.50 to +0.49 8 400% 1+0.50 to +1.49 22 275% 2 +1.50 to +2.49 93 423% 3 +2.50 to +3.49 283 304% 4 +3.50 to +4.49 893 316% 5 +4.50 to +5.49 2,822 316% 6 +5.50 to +6.49 8,768 311% 7 +6.50 to +7.49 26,533 303% 8 +7.50 to +8.49 77,627 293% 9 +8.50 to +9.49 217,689 280% 10 +9.50 to +10.49 626,883 288% 11 +10.50 to +11.49 1,823,573 291% 12 +11.50 to +12.49 5,304,685 291% 13 +12.50 to +13.49 15,431,076 291% 14 +13.50 to +14.49 44,888,260 291% 15 +14.50 to +15.49 130,577,797 291% 16 +15.50 to +16.49 379,844,556 291% 17 +16.50 to +17.49 1,104,949,615 291% 18 +17.50 to +18.49 3,214,245,496 291% 19 +18.50 to +19.49 9,350,086,162 291% 20 +19.50 to +20.49 27,198,952,706 291% 11

12. How many Stars Can You See? • Dark-adapted naked eye (1x7 binoculars) • Can see to magnitude 6.5 -> ~104 stars • Light gathering ability scales with area. • Magnitude Increase = log10(Area increase) / 0.4 • 10x50 binoculars ~50x area -> +4.25 magnitudes • 16” SCT ~64x area -> +4.5 magnitudes • 10m Keck telescope ~625x area -> +7 magnitudes 12

13. How many Stars Can You See? • So for naked eye observing • 10x50 binoculars • 50x area • +4.25 magnitudes (to 10.75) > 106 stars • 16” SCT • 64x area • +4.5 magnitudes (to 15.25) > 108 stars • 10m Keck telescope • 625x area • +7 magnitudes (to 22.75) > 1011 stars 13

14. Figure 10.6Apparent Magnitude 14

15. Light Pollution • Generally not an issue in La Plata county. • Durango has a dark sky ordinance, but only for new construction. • Fort Lewis is making progress with outside light fixtures. 15

16. Light Pollution Earth at Night Credit: C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive 16

17. Light Pollution From IDA Website: http://www.darksky.org/images/sat.html 17

18. Light Pollution You Are Here Observatory 18

19. Figure 10.15Hipparcos H–R Diagram • Plot the luminosity vs. temperature. • This is called a Hertzsprung-Russell (H-R) diagram 19

20. What fraction of the stars on an H-R diagram are on the main sequence • 0-50% • 50-70% • 70-80% • >80% 20

21. What fraction of the stars on an H-R diagram are on the main sequence • 0-50% • 50-70% • 70-80% • >80% 21

22. Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… 22

23. Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… • If a star is on the main sequence, then we know its luminosity. So • If you know brightness and luminosity, you can determine a star’s distance. 23

24. Distance Scale • Spectroscopic Parallax - the process of using stellar spectra to determine distances. • Can use this distance scale out to several thousand parsecs. 24

25. Figure 10.16Stellar Distances 25

26. Stellar Evolution 26

27. Figure 11.16Atomic Motions • Low density clouds are too sparse for gravity. • A perturbation could cause one region to start condensing. 27

28. Figure 11.17Cloud Fragmentation 28

29. Figure 11.20Interstellar Cloud Evolution 29

30. http://discovermagazine.com/2009/interactive/star-formation-game/http://discovermagazine.com/2009/interactive/star-formation-game/ • google “star formation game” 30

31. H-R diagram review • The H-R diagram shows luminosity vs. temperature. • It is also useful for describing how stars change during their lifetime even though “time” is not on either axis. • How to do this may not be obvious. • Exercise - Get in groups of ~four and get out a blank piece of paper. 31

32. Group Exercise • As a group, create a diagram with “financial income” on the vertical axis, and “weight” on the horizontal axis. • Use this graph to describe the past and future of a fictitious person (or a group member). • Label significant events, for example • birth • college • retirement • death 32

33. Stellar Evolution 1 - interstellar cloud - vast (10s of parsecs) 2(and 3) - a cloud fragment may contain 1-2 solar masses and has contracted to about the size of the solar system 4 - a protostar • center ~1,000,000 K • Too cool for fusion, but hot enough to see. (photosphere ~3000 K) • radius ~100x Solar 33

34. How would the luminosity of a one-solar-mass protostar compare to the sun? A) Less than .1x as bright B) A little lower. C) About the same. D) A little brighter E) More than 10x brighter 34

35. How would the luminosity of a one-solar-mass protostar compare to the sun? A) Less than .1x as bright B) A little lower. C) About the same. D) A little brighter E) More than 10x brighter 35

36. Figure 11.19Protostar on the H–R Diagram 36

37. Figure 11.21Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. 37

38. Figure 11.18Orion Nebula, Up Close 38

39. Figure 11.23Protostars 39

40. Figure 11.21Newborn Star on the H–R Diagram 40

41. Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years 41

42. Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years 42

43. Stellar Lifetimes • Proportional to mass • Inversely proportional to luminosity • Big stars are MUCH more luminous, so they use their fuel MUCH faster. • The distribution of star types is representative of how long stars spend during that portion of their life. • Example - snapshots of people. 43

44. Figure 10.21Stellar Masses 44

45. Figure 11.24Prestellar Evolutionary Tracks 45

46. Figure 11.25Brown Dwarfs 46

47. Figure 11.22Protostellar Outflow 47

48. Stellar Evolution 48

49. Figure 11.21Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. 49

50. Figure 11.21Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Can have violent “winds” streaming outwards; often bipolar flow from poles; T-Tauri phase 50