Astronomy midterm question: evening star Jupiter after retrograde ends?

Astronomy 210 Midterm 1, fall semester 2015
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

Pdg: Would Jupiter be an evening star or a morning star after its retrograde motion is complete?
PeT: After retrograde motion ends, Jupiter would be rising at sunset and is thus visible as an evening star.

Explain why this answer is correct, and how you know this. Support your answer using a diagram showing the positions of the sun, Jupiter, Earth, and an observer on Earth.

[*] answers.yahoo.com/question/index?qid=20150730175629AA95Dmw.

Solution and grading rubric:

• p:
  Correct. Complete diagram and reasoning includes the following explanations:
  1. Earth (in an inner orbit than Jupiter) already passes sun-Jupiter line for retrograde motion to be completed;
  2. observer at sunset (6 PM) drawn on Earth such that sun is on the west horizon, with Jupiter already rising up from the east horizon.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Diagram and discussion problematic.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm01sF1A
p: 7 students
r: 10 students
t: 9 students
v: 7 students
x: 6 students
y: 0 students
z: 0 students

Section 70160
Exam code: midterm01nW6b
p: 4 students
r: 4 students
t: 8 students
v: 11 students
x: 4 students
y: 0 students
z: 0 students

A sample "p" response (from student 7520):