1. The Stars HNRT 227 Chapter 14 22 October 2015 Great Idea:
The Sun and other stars use nuclear fusion reactions to convert mass into energy. Eventually, when a star’s nuclear fuel is depleted, the star must burn out.

2. Chapter Outline The Nature of Stars The Anatomy of Stars
The Variety of Stars
The Life Cycles of Stars

3. iClicker Question How often do you look up at the night time sky?
A Always (when possible)
B Often
C Sometimes
D Never

4. iClicker Question
Do you enjoy looking at the stars?
A yes
B no

5. The Nature of Stars

6. The Nature of Stars Astronomy Star
Oldest science (?)
Star
Ball of gas
Fusion reactor
All stars have a beginning and an ending

7. Measuring the Stars with Telescopes and Satellites
Electromagnetic radiation
Measurement of photons
Wavelength
Intensity
Direction
Variation

8. Telescopes

9. Orbiting Observatories
Great Observatories Program
Hubble Space Telescope
Spitzer Infrared Telescope
Chandra X-Ray Observatory

10. iClicker Question What source of data is used to analyze stars?
A chemical testing of actual samples of stellar matter
B electromagnetic radiation
C spacecraft in orbit around distant stars
D both B and C above
E no data is used

11. iClicker Question Telescopes are devices that:
A focus and concentrate radiation
B magnify only visible light
C all use mirrors
D both B and C above

12. The Anatomy of Stars

13. The Structure of the Sun
Stellar core
Radiative zone
Convection zone
Photosphere
Chromosphere
Corona
Solar Wind
Stream of particles

14. Our Sun

15. More On Solar Structure
Hydrogen fusion takes place in a core extending from the Sun’s center to about 0.25 solar radius
The core is surrounded by a radiative zone extending to about 0.71 solar radius
In this zone, energy travels outward through radiative diffusion
The radiative zone is surrounded by a rather opaque convective zone of gas at relatively low temperature and pressure
In this zone, energy travels outward primarily through convection

16. How do we know the Sun’s interior?
Helioseismology is the study of how the Sun vibrates
These vibrations have been used to infer pressures, densities, chemical compositions, and rotation rates within the Sun

17. Magnetic Fields

18. Northern Lights (Aurora Borealis)

19. The Sun’s Energy Source: Fusion
Historical
Current
hydrogen
Fusion
3-steps-hydrogen burning
P + P  D + e+ + neutrino + energy
D + P  3He + photon + energy
3He + 3He 4He + 2protons + photon + energy
Life expectancy
11-12 billion years

20. The Variety of Stars Differences Behavior Color Brightness Total mass
Distance
Absolute brightness
Energy output
luminosity
Apparent brightness
Behavior
Total mass
age

21. The Cosmic Distance Ladder
Light-years
Measurement
Triangulation (parallax)
Spectroscopic parallax
Cepheid variable
Tully-Fisher
Supernovae Type Ia
Hubble’s Law

22. The Hertzsprung-Russel Diagram
Star Groupings
Main-sequence stars
Red giants
White dwarfs

23. Step 1 to an H-R Diagram
Plot for the 20 nearest and brightest stars to Earth

24. Step 2 to an H-R Diagram
Reversing the y-axis

25. Step 3 to an H-R Diagram Reversing the x-axis
Lowest temperature to the right

26. A Standard H-R Diagram

27. iClicker Question Compared with other stars, our Sun is:
A an unusually large star
B not a star at all
C a rather ordinary star

28. iClicker Question
The outer part of the Sun, the part that actually emits most of the light we see, is called the:
A chromosphere
B convective zone
C photosphere
D core
E radiative zone

29. iClicker Question The solar wind is composed of: A bits of neutral gas
B all kinds of organic substances
C air
D charged particles including hydrogen and helium ions

30. iClicker Question Northern lights result from interactions of:
A the Sun’s magnetic field with Earth’s gravity
B UV light from the Sun with Earth’s ozone layer
C the solar wind with the Earth’s magnetic field

31. iClicker Question The Sun’s peak output of energy is in:
A the ultraviolet portion of the electromagnetic spectrum
B the visible portion of the electromagnetic spectrum
C the infrared portion of the electromagnetic spectrum

32. iClicker Question What is the Sun’s energy source?
A combustion of hydrogen rich chemical fuels
B fusion of hydrogen
C fission of hydrogen
D radioactive decay
E gravitational collapse

33. The Life Cycles of Stars

34. The Birth of Stars
Nebular Hypothesis
Laplace

35. The Main Sequence and the Death of Stars
Stars much less massive than the Sun
Glows 100 billion years
No change in size, temperature, energy output
Brown dwarfs
Some don’t consider these stars

36. The Main Sequence and the Death of Stars
Stars about the mass of the sun
Hydrogen burning at faster rate
Move off main sequence
Helium burning
Red giant
Begin collapse
White dwarf

37. The Life Cycle of a Star Like the Sun
Gas cloud
Fragmentation
Protostar
Kelvin-Helmholz contraction
Hayashi Track
Ignition
Adjustment to Main Sequence
Hydrogen Core Depletion
Hydrogen shell burning
Helium flash
Helium core burning
Helium core depletion
Helium shell burning
Helium shell flashes
Planetary nebula
White Dwarf

38. Sun’s Life Cycle on H-R Diagram

39. The Main Sequence and the Death of Stars
Very Large Stars
Successive collapses and burnings
Iron core
Catastrophic collapse
supernova

40. Layers of Massive Star Si -> Fe Mg -> Ne -> Mg O ->
C -> O
He -> C
H -> He Fe
Layers of
Nuclear
Fusion in
High
Mass
Stars

41. Neutron Stars and Pulsars
Dense and small
High rotation rate
Little light
Pulsar
Special neutron star
Electromagnetic radiation
End state of supernova

42. Black Holes Black Hole Result of collapsed large star
Nothing escapes from surface
Cannot “see” them
See impact on other stars, dust, etc.
Detect x-rays, gamma rays

43. iClicker Question
It is estimated that the total lifetime of our Sun is 12 billion years. Roughly, how far is it through its hydrogen-burning phase now?
A 10%
B 25%
C 50%
D 90%

44. iClicker Question
Triangulation and Cepheid variables are methods to measure:
A distances to stars
B energy output of stars
C lifetime of stars
D composition of stars

45. iClicker Question
A Hertzsprung-Russell diagram plots a star’s temperature versus its:
A color
B distance
C age
D size
E energy output

46. iClicker Question
Large dust and gas clouds are commonly found throughout space. They are called:
A red giants
B galaxies
C nebulae
D supernovae
E white dwarfs

47. iClicker Question
The fusion process in very large stars produces chemical elements up to:
A He
B C
C Fe
D U
E Pb

48. iClicker Question All natural elements beyond iron are created in:
A supernova explosions
B fusion of very large stars
C the big bang

49. iClicker Question
An object that is so dense and massive that nothing, including light can escape from its surface is called:
A a supernova
B a red giant
C a white dwarf
D a black hole
E a neutron star

50. iClicker Question
Are you surprised that the chemical elements about you were made in a supernova?
A Yes
B No