Astronomy midterm question: other galaxies but our own visible?

Astronomy 210 Midterm 2, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

[20 points.] Even though only a small fraction of the stars in own galaxy is visible from Earth, explain why we can still see stars of other galaxies outside the Milky Way with the naked eye. Support your answer using a diagram, and properties of galaxies.

Solution and grading rubric:

• p = 20/20:
  Correct. Views along the disk of the Milky Way would be obscured by interstellar gas/dust, but views up and down, perpendicular to the plane of the Milky Way disk would be much less obscured, as space between galaxies is relatively empty, making the stars of galaxies visible.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. At least understands how shape of Milky Way is important, but may discuss other contributing factors.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discusses some other aspects of the Milky Way.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 30674
Exam code: midterm02N3n4
p: 14 students
r: 9 students
t: 6 students
v: 9 students
x: 0 students
y: 2 students
z: 0 students

A sample "p" response (from student 1450):