1. Discussion As the Sun ages on the main sequence, it continually converts four hydrogen atoms into one helium atom. Can we measure how much of the core has been turned into helium? Explain.

3. Discussion Using the concepts of hydrostatic and thermal equilibrium explain how the Sun changes on the H-R diagram as He builds up in the core before it runs out of core hydrogen.

7. Discussion In about 5 billion years the Sun will run out of hydrogen in its core. What happens to the Sun’s equilibrium?

9. Discussion What happens to the Hydrogen that was just outside the core but never hot enough to fuse into He?

10. Discussion The fusion of H into He around the Sun’s core produces a lot of heat and pressure. Can this stop the contraction of the core? What effect does this extra pressure have on the outer layers of the Sun?

12. Discussion What happens to helium produced during hydrogen shell burning?

13. Discussion After a star leaves the main sequence how does its position on the main sequence change?

18. Electron degeneracy pressure Electrons cannot occupy the same place. When electrons are packed as tightly as they can be we call this state degenerate. Pressure does not depend on temperature, and stops core contraction in red giant stars

20. Discussion Do you think stellar winds will be stronger, less than, or about the same in red giant stars as in main sequence stars? Explain.

22. Betelgeuse

24. Triple alpha process As long as more He is dumped on the core it continues to contract, to heat up and the star’s outer layers continue to expand. Eventually, the core reaches a temperature of 100 million K and 3 He atoms can fuse into a carbon atom.

27. Discussion What do you think happens to the hydrogen burning shell as the star’s core expands? How does this affect the temperature and luminosity of the star?

30. Discussion A solar mass star will only last on the horizontal giant branch for about 100 million years. Why does the core helium burning stage of a star not last as long as the core hydrogen burning stage?

31. Discussion What do you think happens when the He in the core of a star runs out?

35. Ring nebula

37. Abell 39

38. Owl nebula

39. Saturn nebula

40. Cat’s Eye nebula

41. Spirograph nebula

42. NGC 7027

43. Stingray nebula

44. NGC 6543

45. MyCn 18

47. Discussion Explain why a star expands when its core collapses once it runs out of hydrogen in its core.

48. Discussion What happens to helium produced during hydrogen shell burning?

49. Discussion What stops the inert core of a red giant star from collapsing?

50. Discussion What do you think happens to the extremely hot white dwarf star as it ages? How does its position on the H-R diagram change?