Cuesta College, San Luis Obispo, CA
[20 points.] Why does an observer see a total lunar eclipse lasting much longer than a total solar eclipse? Defend your answer using a diagram showing the positions of an observer, Earth, the moon, and shadow zones.
Solution and grading rubric:
- p = 20/20:
Correct. The size of the umbra created by the Moon makes total solar eclipses last only a few minutes, as the umbral spot passes quickly over an observer's position. The size of the umbra created by the Earth makes total lunar eclipses last a few hours, as it will take that long for the Moon to pass through this shadow zone of the Earth. Has a correct explanation, and clear, correct diagrams of a total solar eclipse and a total lunar eclipse demonstrating the effect of umbra sizes. - r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Typically incomplete or inconsistent diagrams. - t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Diagrams problematic, but at least recognizes importance of sizes of umbrae. - v = 8/20:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Plausible arguments involving varying orbital speeds, precession of nodes, varying orbital distances, with some attempt at diagrams. Or substantively correct diagrams only. - x = 4/20:
Implementation/application of ideas, but credit given for effort rather than merit. Involving unrelated factors. - y = 2/20:
Irrelevant discussion/effectively blank. - z = 0/20:
Blank.
Section 30674
p: 8 students
r: 6 students
t: 7 students
v: 17 students
x: 2 students
y: 0 students
z: 0 students
A sample "p" response (from student 1959):
A sample "t" response (from student 1889):
A sample "v" response, with diagram only (from student 1213):
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