Astronomy 210 Quiz 4, Fall Semester 2008
Cuesta College, San Luis Obispo, CA
[4.0 points.] Sirius A is a star that has an apparent magnitude m = –1.5 and an absolute magnitude M_v = +1.41. Approximately how far away is Sirius A 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.
Section 70158
(A) : 9 students
(B) : 14 students
(C) : 0 students
(D) : 45 students
Correct answer: (D)
When brought to the "fair distance" of 10 parsecs (thus changing its apparent magnitude to absolute visual magnitude), Sirius A now seems to be dimmer, indicating that it must have moved away to the Earth during this process. Thus Sirius A must be closer than this fair distance of 10 parsecs.
"Difficulty level": 67%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64
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