Astronomy quiz question: distance from apparent and absolute magnitudes

Astronomy 210 Quiz 4, Spring Semester 2010
Cuesta College, San Luis Obispo, CA

61 Ursae Majoris is a star that has an apparent magnitude m = +5.31 and an absolute magnitude M_V = +5.41. How far away is 61 Ursae Majoris from Earth?
(A) Much farther away than 10 parsecs.
(B) A little farther away than 10 parsecs.
(C) Exactly 10 parsecs away.
(D) Closer than 10 parsecs away.

Correct answer: (D)

61 Ursae Majoris appears to be +5.31 as seen from its true distance from Earth, but when placed at the "fair" distance of 10 parsecs away, its becomes slightly dimmer (+5.41). Thus it was pushed back to get to 10 parsecs, and was located closer than 10 parsecs away from Earth.

Section 30674
(A) : 1 student
(B) : 8 students
(C) : 2 students
(D) : 32 students

"Success level": 76% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.58

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