Astronomy clicker question: star cluster lookback time and evolution rates

Astronomy 210, Spring Semester 2009
Cuesta College, San Luis Obispo, CA

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the beginning of their learning cycle:


Which star's light takes the shortest time to travel to us?
(A) O5 star.
(B) B0 star.
(C) A5 star.
(D) (There is a tie.)
(E) (I'm lost, and don't know how to answer this.)

Section 30674 (pre-)
(A) : 12 students
(B) : 2 students
(C) : 1 student
(D) : 6 students
(E) : 3 students

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Section 30674 (post-)
(A) : 10 students
(B) : 0 students
(C) : 0 students
(D) : 13 students
(E) : 1 student

Correct answer: (B)

Since these stars are in the same cluster, and are all located at the same distance away, light from all three stars will take the same amount of time to travel to us.

Pre- to post- peer-interaction gains:
pre-interaction correct = 25%
post-interaction correct = 54%
Hake (normalized) gain <g> = 39%

[Follow-up question.]
Which star's supernova explosion (type II or type Ia) was/will be observed last by us?
(A) O5 star.
(B) B0 star.
(C) A5 star.
(D) (There is a tie.)
(E) (I'm lost, and don't know how to answer this.)

Section 30674 (pre-)
(A) : 1 students
(B) : 2 students
(C) : 18 students
(D) : 1 students
(E) : 3 students

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Section 30674 (post-)
(A) : 2 students
(B) : 0 students
(C) : 21 students
(D) : 0 students
(E) : 2 students

Correct answer: (C)

Massive stars will have shorter main sequence lifetimes, while low-mass stars will have longer main sequence lifetimes. Since these stars are located in the same cluster, and thus were born at the same time, and are located the same distance away from us, the lowest-mass star will be seen to end its main sequence lifetime last.

Pre- to post- peer-interaction gains:
pre-interaction correct = 72%
post-interaction correct = 84%
Hake (normalized) gain <g> = 43%