Astronomy quiz question: parallax angle and parsecs

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

Proxima Centauri is a star that has a parallax angle just a little smaller than 1 arcsecond. Approximately how far away is Proxima Cenaturi?
(A) Much farther away than 1 parsec.
(B) A little farther away than 1 parsec.
(C) Exactly 1 parsec away.
(D) Closer than 1 parsec away.

Correct answer: (B)

A star that is exactly 1 parsec away would have a parallax angle of 1 arcsecond. A closer star would have a larger parallax angle. With a parallax angle slightly smaller than 1 arcsecond, the star would be slightly farther away than 1 parsec. (A star with a parallax angle much smaller than 1 arcsecond would be much farther away than 1 parsec.)

Section 70158
(A) : 10 students
(B) : 15 students
(C) : 2 students
(D) : 18 students

"Success level": 39% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.08

Section 70160
(A) : 2 students
(B) : 13 students
(C) : 4 students
(D) : 22 students

"Success level": 38% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.36