Name: ________________________


                                        Student Number: ______________

• SIT in the seat corresponding to the SEAT NUMBER ON THE EXAM.
• If you answer on the exam, leave that question blank on the bubble sheet.
• Do the easiest questions first.
• If you have the slightest doubt about what a question is asking -- ask a proctor.
• If you feel no choice for answers to a question are correct, write what you think is the correct answer and note the question number on this page.
• Do NOT open the exam until it is time to start.
• DON'T PANIC! GOOD LUCK!

1. (3 Pts) If particles (atoms, molecules, electrons) are moving slowly, this means that the material is
   1. hot
      
   2. cold
      
   3. dense
      
   4. diffuse
      
   5. undergoing nuclear reactions
      

2. (3 Pts) When an electron emits a photon, the electron's energy
   1. increases
      
   2. decreases
      
   3. stays the same
      
   4. the energy could change in any of these ways
      

3. (3 Pts) Which of the following stars emits the reddest light?
   1. Procyon
      
   2. Capella
      
   3. Pollux
      
   4. Vega
      
   5. Spica
      

4. (3 Pts) You observe light with the following wavelengths: 1000, 3000, 5000, 10000, and 12000 angstroms. Which of these has the least energy?
   1. 1000
      
   2. 3000
      
   3. 5000
      
   4. 10000
      
   5. 12000
      

5. (3 Pts) Arrange the following types of light in order of decreasing energy. That is, start with highest-energy type of light.
   1. infrared, visible, ultraviolet, radio, microwave
      
   2. radio, infrared, visible, ultraviolet, microwave
      
   3. visible, radio, microwave, infrared, ultraviolet
      
   4. ultraviolet, visible, infrared, microwave, radio
      
   5. microwave, radio, ultraviolet, visible, infrared
      

6. (5 Pts) Describe what happens to the atom when it absorbs a photon.

   The atom gains the energy of the photon and an electron jumps to a larger, higher energy orbit. For an electron to jump to a higher energy orbit it must absorb a photon with exactly the right amount of energy equal to the difference between the higher and lower energy orbits. If the photon has enough energy the electron may jump completely out of the atom and leave the atom.

7. (3 Pts) What astronomical instrument records light?
   • CCD
   • photographic film
   • photometer
   • spectrograph
   • detector

8. (3 Pts) What astronomical instrument gathers light?

   Telescope

9. (3 Pts) Astronomers have measured the following parallaxes of the stars ISP alpha=0.01, ISP beta=0.07, ISP gamma=0.001, ISP delta=0.03, and ISP epsilon=0.005 arcseconds. Which star is closest?
   1. ISP alpha
      
   2. ISP beta
      
   3. ISP gamma
      
   4. ISP delta
      
   5. ISP epsilon
      

10. (3 Pts) The stars Deneb and Castor emit the same amount of radiation from each square meter of their surface, but Deneb is about 1000 times more luminous than Castor. The reason is

    Deneb is larger. It has 1000 times more surface area than Castor

11. (4 Pts) Look at the following two stellar spectra. Which of the stars is hotter?

    Star A
    Star B

    Explain why you selected this star.

    Cool stars have strong Ca lines and weak H lines.
    Hot stars (10,000K, type A0) have weak Ca lines and strong H lines
    Very Hot stars have weak Ca lines and weak H lines.
    (You need to look at both calcium and hydrogen lines.)

12. (4 pts) Look at the stars Arcturus, Antares, Capella, Pollux and Aldebaran in the attached HR Diagram. Which star is the bluest?

    Capella

13. (3 Pts) In terms of the behavior of particles (atoms, molecules, electrons), describe how pressure is produced.

    Pressure is produced by colliding particles. The hotter the particles the faster they move and the more and harder the collisions are. The denser the particles, the closer together they are and the more collisions. Both hotter and denser make more pressure.

14. (3 Pts) The standard model for stellar structure has nuclear fusion as the mechanism for energy generation. Why was the earlier theory of gravitational contraction as the source of energy for the Sun rejected?
    1. Astronomers calculated that the Sun was hot enough in the center to have nuclear fusion.
       
    2. Astronomers discovered that the Sun was composed mostly of hydrogen.
       
    3. Since the standard model failed the neutrino test, it must be rejected.
       
    4. A new theory does have gravitational contraction as the source for the Sun's energy.
       
    5. Gravitational contraction would not supply energy for a long enough time.
       

15. (3 Pts) The source of the Sun's energy is
    1. The fusion of hydrogen into helium.
       
    2. The fusion of hydrogen into carbon and oxygen.
       
    3. The fusion of hydrogen into iron.
       
    4. The fusion of helium into carbon and oxygen.
       
    5. The fusion of hydrogen and helium.
       

16. (4 Pts) Apply the balance conditions that determine the structure of a star to explain what would happen if the temperature in the core of a star decreased. Circle the correct choice in each triplet in the paragraph below.

    If the the temperature in the core decreases, the pressure in the core would (decrease) (remain unchanged) (increase). Then the pressure will be (less than) (the same as) (greater than) the gravity. So the core of the star will (contract) (not change) (expand). As a result the temperature in the core will (decrease) (remain unchanged) (increase), and also the insulating ability of the star will (decrease)(remain unchanged) (increase). As a result of this (possible) change in temperature, the rate of energy generation in the core (decrease) (remain unchanged) (increase) and the presure in the core will (decrease) (remain unchanged) (increase). As a result of the (possible) change in insulating ability, the luminosity of the star will (decrease) (remain unchanged) (increase). As a result, the star will come into balance again.

17. (4 Pts) Name one successful test of the standard stellar model.
    • Helioseismology
    • HR diagram of star clusters
    • Mass-Luminosity Relation for main-sequence stars

18. (3 Pts) What will happen after the Sun runs out of hydrogen in its core?
    1. The core will contract and get hotter, triggering fusion of helium into carbon and oxygen.
       
    2. The core will contract and get hotter, triggering fusion of hydrogen to helium in a shell.
       
    3. The core will cool off and shrink, then turn into a white dwarf.
       
    4. The core will cool off and shrink, triggering a supernova.
       
    5. The core will contract and get cooler, and the entire Sun will undergo gravitational contraction.
       

19. (3 Pts) There are two stars which both began on the main-sequence with one solar mass. One is now a red giant, and the other is a main-sequence star. The primary difference in their internal structure which makes them look so different is
    1. The red giant is probably much older.
       
    2. The red giant fuses helium to iron in its core.
       
    3. The red giant fuses hydrogen to helium in a shell around its hot helium core.
       
    4. The red giant fuses carbon and oxygen in its core to magnesium and silicon.
       
    5. The red giant is composed mostly of helium, which increases the insulating ability and makes it expand.
       

20. (3 Pts) The last stage in the Sun's life will be as
    1. a supernova.
       
    2. a black hole.
       
    3. a neutron star.
       
    4. a white dwarf.
       
    5. a red giant.
       

21. (3 Pts) The last stage in the bluish supergiant Deneb's life will be as
    1. a supernova.
       
    2. a black hole.
       
    3. a neutron star.
       
    4. a white dwarf.
       
    5. a red giant.
       

22. (5 Pts) Calculate the total mass of the two stars in the binary stellar system Alderan.
    The system is 10 parsecs distant from the Sun. One is a main sequence star of type F0 and luminosity of 10 times that of the Sun, and the other is a G2 star with luminosity the same as the Sun. The stars orbit around each other at a speed of 20 km/s, with a period of 3 years at a separation of 3 AUs. Use one of the following formulae:

    F = m a
    lambda_peak=3x10⁷ / T
    P²=a³
    m₁ + m₂ = a³/P²
    E = m c²
    D=1/p

    m₁ + m₂ = a³/P²
    m₁ + m₂ = 3[AU]³ / 3[yrs]²
    m₁ + m₂ = 27 / 9
    m₁ + m₂ = 3 M_Sun

23. (3 Pts) Arrange the following astronomical bodies in order of decreasing size. That is, start with the object with the largest radius.
    1. Earth, red giant, Sun, black hole, neutron star
       
    2. red giant, Sun, Earth, black hole, neutron star
       
    3. black hole, red giant, neutron star, Sun, Earth
       
    4. Sun, red giant, Earth, neutron star, black hole
       
    5. red giant, Sun, Earth, neutron star, black hole
       

24. (3 Pts) Arthur Eddington, in the 1920's, suggested that nuclear fusion rather than gravitational contraction was the source of energy in the Sun based on
    1. Einstein's new equation, E=mc².
       
    2. An understanding that the stability and mass of the Sun requires the interior to be very hot and dense.
       
    3. The mass-luminosity relation of the main-sequence stars on a Hertzsprung-Russell Diagram.
       
    4. Radioactive carbon dating of old rocks on the surface of the Earth.
       
    5. He used all of these ideas.

25. (5 Pts) Sketch the structure of a 10-solar-mass star on the main-sequence. Show the regions where fusion reactions are occurring, if any. Label the composition of the different regions.

    

26. (5 Pts) Sketch the internal structure of the star Arcturus. Show the regions where fusion reactions are occurring, if any, and write down the process. Label the composition of the different regions.

    

27. (3 Pts) Which of the following stars will have the longest lifetime on the main-sequence?
    1. Procyon because it has the smallest mass.
       
    2. Fomalhaut
       
    3. Castor
       
    4. Regulus
       
    5. Altair.
       

28. (4 pts) The structure of a star is determined by two equilibrium or balance conditions. These are the balance between

    Pressure and Gravity
    and
    Energy Generation and Energy Loss

29. (3 Pts) Energy is transported out of a star's core by
    1. electrons.
       
    2. photons.
       
    3. hydrogen atoms.
       
    4. helium atoms.
       
    5. all of these.
       

30. (5 Pts) On the sky map for September below draw small circles around as many of the stars from your list of 16 brightest northern hemisphere stars as you can find and write their names next to each such star. [One point for each correct star, but minus 1/2 point for each incorrect star, so don't guess.]

    There were seven stars. However, since several stars were on the edge and difficult to find, we gave extra credit for identifying more than five stars.

    

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