1. The main sequence lifetime of a star is determined primarily by
   1. the position in the Galaxy where it formed
   2. the amount of hydrogen that it has
   3. the amount of helium that it has
   4. its radius
   5. its surface temperature

   
   
   

2. All main sequence stars
   1. are the same physical age
   2. fuse hydrogen in their cores
   3. have the same luminosity
   4. have the same radius
   5. have the same mass

   
   
   

3. When Hydrogen is fusing in a thin shell around the core, which of the following will happen?
   1. the core will expand
   2. the core will collapse
   3. the envelope will expand
   4. the star will explode as a supernova
   5. both b and c will happen

4. Electron degeneracy occurs whenever matter becomes
   1. very hot
   2. very cold
   3. very old
   4. very dense
   5. completely ionized

5. The main-sequence mass of a star is not a good predictor of its evolutionary endpoint (e.g. white dwarf, neutron star or black hole) because
   1. the mass of a star can change significantly during its main sequence lifetime
   2. interactions with other stars cause mass to be ripped away
   3. this only depends on how much carbon is in the core which varies from star to star
   4. the mass of the star continues to increase when heavier and heavier elements are produce inside its core
   5. none of the above

6. A hypothetical cluster of stars is observed to have no main sequence stars more massive than 0.5 solar masses. The approximate age of this cluster would be:
   1. 1 million years
   2. 10 million years
   3. 100 million years
   4. 1 billion years
   5. 10 billion years
   6. 100 billion years

   
   
   
   The last set of questions refers to this HR diagram. There are 10 stars and 10 possible choices on your keypads (the 0 key equals 10 for this exercise).

7. Which star has the largest radius?

8. Which star has the longest main sequence lifetime?

9. Which star is most like our sun?

10. Which star is fusing helium in its core?

11. Which star is supported by electron degeneracy?

12. Which star outputs the highest amount of ultraviolet photons?

13. Which star is the coolest?

14. Which star is the least massive?

15. Which star has a main sequence liftetime of about 1 billion years?