Astronomy midterm question: 12 hours between Mercury setting and Venus rising?

Astronomy 210 Midterm 1, fall semester 2019
Cuesta College, San Luis Obispo, CA

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

J.F.: Can an observer ever witness Mercury setting at the same time while Venus is rising?
rzfr: No, that is impossible. It will take about 12 hours between Mercury setting and Venus rising.

Discuss why it would take about 12 hours between Mercury setting and Venus rising for an observer in San Luis Obispo, CA, and how you know this. Support your answer using a diagram showing the positions of the sun, Mercury, Venus, Earth, and an observer on Earth.

[*] answers.yahoo.com/question/index?qid=20090328072648AALZoVS.

Solution and grading rubric:

• p:
  Complete diagram and reasoning includes the following explanations for why there would be about 12 hours between Mercury setting and Venus rising:
  1. places observer on Earth at sunset to watch Mercury (in an inner orbit) setting in the west; and
  2. places observer on Earth at sunrise to watch Venus (in an inner orbit) rising in the east.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Typically diagram is correct, but supporting argument is contradictory or incomplete. May have placed Mercury to rise at sunrise and placed Venus to set at sunset.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Still has Mercury and Venus along inner orbits around the sun.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at diagram(s), but no clear indication of observer/horizon on Earth and/or placement of inner planets. Typically misplaces Mercury and Venus in their relative outer/inner orbits around the sun.
• 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: midterm01Sw3e
p: 20 students
r: 4 students
t: 5 students
v: 6 students
x: 0 students
y: 0 students
z: 1 student

Section 70160
Exam code: midterm01N0dL
p: 6 students
r: 5 students
t: 5 students
v: 7 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1234):