Name: ________________________


                                        Student Number: ______________

1. (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.

2. (4 Pts) Name one successful test of the standard stellar model.

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3. (3 points) What is the primary reason why stars must evolve?
   1. They move on the Hertzsprung-Russell diagram.
   2. They are born with differing masses.
   3. They are orbiting around the galaxy.
   4. They are losing energy.
   5. They are composed mostly of hydrogen and helium.

4. (8 pts) Hertzsprung-Russell (HR) Diagram
   On the Hertzsprung-Russell (HR) diagram below plot points representing the Luminosity and Surface Temperature of the 16 brightest stars in the Northern Hemisphere from your list. The values of the luminosity [in units of the Sun's luminosity (L_Sun)] and the surface temperature for each star are given on your list. Label each star with its name. Circle the regions of the Main Sequence and Red Giants
   

5. (3 pts) The largest of the following stars is:
   
   1. Procyon
      
   2. Pollux
      
   3. Betelgeuse
      
   4. Spica
      
   5. Antares

6. (5 Pts) Sketch the internal structure of the star Arcturus. Show the regions where nuclear fusion reactions are occurring, if any, and write down the process. Label the composition of the different regions.

7. (3 Pts) Which of the following stars will have the longest lifetime on the main-sequence?
   1. Altair.
   2. Castor
   3. Fomalhaut
   4. Procyon
   5. Regulus

8. (3 points) Altair will end its life as a
   1. neutron star
   2. supernova
   3. white dwarf
   4. black hole
   5. none of these

9. (4 points) Use the Mass - Luminosity relation, shown on the web or Figure 10.21, to explain why small mass stars have longer lives than large mass stars.

10. (4 points) Estimate the mass of Altair.

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