Compared with the 2.5-m diameter Mount Wilson telescope, each of the 10-m diameter Keck telescopes has a greater light-gathering power by a factor of
A) 4.
B) 16.
C) 2.
D) 1; they have the same light-gathering capability.

Question

Quizplus · Accepted Answer

The light-gathering power of a telescope is proportional to the area of its mirror, which is proportional to the square of its diameter. Therefore, comparing the 10-m diameter Keck telescopes to the 2.5-m diameter Mount Wilson telescope, the factor increase in light-gathering power is (10/2.5)^2 = 4^2 = 16.