Cuesta College, San Luis Obispo, CA
Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle, during a review session before a midterm:
The H-R diagram of a star cluster shown at right shows: (A) stars that are all old.
(B) stars that are all young.
(C) stars that are a mixture of young and old stars.
(D) (This H-R diagram is not possible for a star cluster.)
(E) (I'm lost, and don't know how to answer this.)
Section 70160
(A) : 12 students
(B) : 1 student
(C) : 11 students
(D) : 1 student
(E) : 0 students
This question was not asked again after displaying the tallied results, but was discussed with the whole class with the instructor facilitating students who gave opinions on either (A) or (C).
Correct answer: (A)
Low-mass protostars take a very long time to reach the main sequence; while massive stars take a very short time to reach the main sequence. Low-mass stars also never leave the main sequence (this is yet to happen, and would require about three times the current age of the universe).
Some students had thought that the massive main sequence stars signaled a young star cluster, while the low-mass stars had left the main sequence, indicating a very old star cluster.
Student: "All stars in a star cluster have to be the same age!"
Pre- to post- peer-interaction gains: (N/A)
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