Astronomy midterm question: wider or longer telescope?

Astronomy 210 Midterm 1, spring semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] Decide whether the diameter, or the length of an optical telescope would be more important in making a decision on a new purchase (or if they would be equally important). Explain why in terms of the properties of telescopes and telescope powers.

Solution and grading rubric:
  • p = 20/20:
    Correct. Discusses how diameter of primary lens/mirror determines the light-gathering power and resolving power, while the (focal) length determines the magnifying power, the latter of which is the least important due to priority given to collecting light that will result in bright, resolvable images worth magnifying.
  • r = 16/20:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Explains how light-gathering power and resolving power depend on diameter and discusses their priority, but does not adequately explain magnification and/or why it would be less important. Or correctly discusses how diameter and length affect respective telescope powers, but gives equal priority to magnification with light-gathering power and resolving power.
  • 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. May confound length and diameter dependence of telescope powers, but generally holds magnification less important than light-gathering and resolving powers.
  • x = 4/20:
    Implementation/application of ideas, but credit given for effort rather than merit. Primarily makes a decision without substantive discussion of relevant telescope powers.
  • y = 2/20:
    Irrelevant discussion/effectively blank.
  • z = 0/20:
Grading distribution:
Section 30674
p: 19 students
r: 11 students
t: 0 students
v: 11 students
x: 3 students
y: 0 students
z: 0 students

Section 30676
p: 33 students
r: 11 students
t: 14 students
v: 16 students
x: 7 students
y: 0 students
z: 1 student

A sample "p" response (from student 0928):

Another sample "p" response (from student 1187):

Another sample "p" response (from student 4733), averring that "wider is better":

Another sample "p" response (from student 1802):

Another sample "p" response (from student ):

Another sample "p" response (from student 0002), with interesting priorities and qualifiers:

Another sample "p" response (from student 0165), illustrating the lament and remorse of an uninformed telescope buyer in comic strip format:

A sample "r" response (from student 6924):

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