Astronomy clicker question: planet-hunting

Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q3.1

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

[0.3 points.] How can you determine if a bright object in the sky is a planet (and not a star), without using a telescope?
(A) If it does not twinkle.
(B) If it does not show up on a starwheel.
(C) If it does not appear in exactly the same location in the sky each night.
(D) (All of the above choices (A)-(C).)

Correct answer: (D)

The large angular diameter of planets make them less susceptible to atmosphere turbulence, so they do not seem to "twinkle" like point-like stars (response (A)). Planets also move with respect to the background stars as they (and the Earth) move around the Sun, and thus cannot be permanently positioned on a starwheel (responses (B) and (C)). Thus the most correct, inclusive answer is (D).

Student responses
Section 4160
(A) : 6 students
(B) : 1 student
(C) : 10 students
(D) : 13 students