Astronomy quiz question: Mercury and Venus low in the east at sunrise?

Astronomy 210 Quiz 3, fall semester 2016
Cuesta College, San Luis Obispo, CA

The locations of Mercury and Venus are shown in the diagram below (not to scale, and orbits have been simplified as circles instead of ellipses).


Mercury and Venus will both be low above the east horizon at sunrise when Earth is located at:
(A) position (A).
(B) position (B).
(C) position (C).
(D) position (D).
(E) (None of the above choices.)

Correct answer (highlight to unhide): (C)

If a line is drawn from Earth to the sun, the observer at sunrise (6 AM) is located perpendicular to that line. Everything below that line would be below the horizon, such that it would not be visible at that time. Doing this for all possible positions of Earth shows that both Mercury and Venus would be visible above the east horizon at sunrise only when Earth is at position (C).


(When Earth is at position (A), only Venus would be visible above the east horizon at sunrise; neither Mercury nor Venus would be visible at sunrise when Earth is at position (B); and only Mercury would be visible above the east horizon at sunrise when Earth is at position (D).)

Section 70158
Exam code: quiz03S7ew
(A) : 8 students
(B) : 10 students
(C) : 12 students
(D) : 8 students
(E) : 0 students

Success level: 37% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.15

Section 70160
Exam code: quiz03n0oN
(A) : 11 students
(B) : 4 students
(C) : 9 students
(D) : 3 students
(E) : 0 students

Success level: 41% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.57