Astronomy midterm question: light-gathering power

Astronomy 10 Midterm 1, Summer Session 2007
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal M1.3

[3.0 points.] Which one of the following choices best explains why telescopes with larger diameter objective mirrors are better than telescopes with smaller diameter objective mirrors?
(A) More light can be collected.
(B) Wider field of view.
(C) Easier to adapt its optics for different people.
(D) It is cheaper to make mirrors as large as possible.
(E) Better atmospheric seeing.

Correct answer: (A).

Light-gathering power is the ability to see dim objects, and depends on the area of the objective mirror (and thus proportional to the square of the diameter). As for (B), if the mirror had a longer focal length (which is not necessarily related to the diameter), then it would have a higher magnification power, and thus a narrower field of view. The other choices (C)-(E) are merely garbled distractors.

Student responses
Section 8027
(A) 7 students
(B) 5 students
(C) 0 students
(D) 0 students
(E) 1 student

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