By approximately how many magnitudes is the star Sirius fainter than the full Moon in our sky? (See Figure 10-2,Comins,Discovering the Essential Universe,6th ed.)
A) 15
B) 2
C) 11
D) 5

Question

Quizplus · Accepted Answer

According to Figure 10-2 in Comins' Discovering the Essential Universe, 6th ed., the apparent magnitude of Sirius is approximately -1.5 while the apparent magnitude of the full Moon is approximately -12.5. Taking the difference between the two magnitudes gives us (-1.5) - (-12.5) = 11, which means that Sirius is approximately 11 magnitudes fainter than the full Moon in our sky. Therefore, the best choice is C) 11.

By Approximately How Many Magnitudes Is the Star Sirius Fainter