Astronomy quiz question: 61 Ursae Majoris

Astronomy 210 Quiz 4, fall semester 2012
Cuesta College, San Luis Obispo, CA

61 Ursae Majoris is a star that is located a distance 9.5 parsecs away from Earth, and has an apparent magnitude of m = +5.3.  Its absolute magnitude M_V is:
(A) –5.3.
(B) 0.
(C) +5.2.
(D) +5.4.
(E) +9.5.

Correct answer: (D)

The apparent magnitude of Tau Ceti, which is the brightness as seen from Earth, will get dimmer as it is moved farther away from 9.5 parsecs to 10 parsecs. Since this is a very small increase in distance, then the absolute magnitude (its brightness at 10 parsecs away) would only be slightly dimmer than the apparent magnitude (its brightness at 9.5 parsecs away).

Section 70160
Exam code: quiz04nNm5
(A) : 3 students
(B) : 2 students
(C) : 8 students
(D) : 11 students
(E) : 2 students

Success level: 47% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.34