Astronomy quiz question: apparent magnitude and distance

Astronomy 210 Quiz 4, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

[Version 1]
Achernar is a star located 36.2 parsecs away from Earth, and has an apparent magnitude of m = +0.51. If Achernar were relocated to 10 parsecs away from Earth, its apparent magnitude would:
(A) get brighter.
(B) remain the same.
(C) get dimmer.
(D) (Not enough information is given.)

Correct answer: (A)

The apparent magnitude would get brighter, as the star would be moving closer to Earth.

Section 70158
(A) : 32 students
(B) : 4 students
(C) : 7 students
(D) : 1 student

Success level: 74% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.46

[Version 2]
Ross 154 is a star located 4.08 parsecs away from Earth, and has an apparent magnitude of m = +13.3. If Ross 154 were relocated to 10 parsecs away from Earth, its apparent magnitude would:
(A) get brighter.
(B) remain the same.
(C) get dimmer.
(D) (Not enough information is given.)

Correct answer: (C)

The apparent magnitude would get dimmer, as the star would be moving closer away from Earth.

Section 70160
(A) : 0 students
(B) : 0 students
(C) : 43 students
(D) : 0 students

Success level: 100% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0