Astronomy quiz question: distance from apparent and absolute magnitudes

Astronomy 210 Quiz 4, fall semester 2014
Cuesta College, San Luis Obispo, CA

Aspidiske is a star with an apparent magnitude m = +2.21 and absolute magnitude M = –4.4. Aspidiske is located __________ from Earth.
(A) farther than 10 parsecs.
(B) exactly 10 parsecs.
(C) closer than 10 parsecs.
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

Aspidiske appears to be +2.21 as seen from its true distance from Earth, but when placed at the "fair" distance of 10 parsecs away, its becomes much brighter (–4.4). Thus it was brought much closer to Earth when moved to 10 parsecs, and was located much farther than 10 parsecs away from Earth.

Section 70158
Exam code: quiz05sP1d
(A) : 28 students
(B) : 1 student
(C) : 7 students
(D) : 9 students

Success level: 75% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.37

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