Astronomy quiz question: August 2017 partial solar eclipse in San Luis Obispo, CA

Astronomy 210 Quiz 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

A total solar eclipse will occur on August 21, 2017 for many observers in the United States[*]. During this event, observers San Luis Obispo, CA will only see a partial solar eclipse[**], because they will be located in:
(A) the moon's umbra.
(B) the moon's penumbra.
(C) the moon's negative shadow.
(D) Earth's umbra.
(E) Earth's penumbra.

[*] eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html.
[**] timeanddate.com/eclipse/in/usa/san-luis-obispo?iso=20170821.

Correct answer: (B)

An observer in the moon's penumbra will see a partial solar eclipse, while an observer in the moon's umbra will see a total solar eclipse. (The "negative shadow" refers to the antumbra of the moon.)

Section 30674
Exam code: quiz02n1hT
(A) : 2 students
(B) : 17 students
(C) : 0 students
(D) : 2 students
(E) : 2 students

Success level: 76% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38

Section 30676
Exam code: quiz02sNoO
(A) : 3 students
(B) : 28 students
(C) : 1 student
(D) : 3 students
(E) : 7 students

Success level: 69% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64

Astronomy quiz question: next full moon after total lunar eclipse

Astronomy 210 Quiz 2, fall semester 2015
Cuesta College, San Luis Obispo, CA

Observers in San Luis Obispo, CA will see a total lunar eclipse in the evening of September 27, 2015.[*][**] There will not be a total lunar eclipse in the following month because:
(A) the moon always keeps the same side facing Earth.
(B) the moon's orbit around Earth is tilted.
(C) the moon's orbit is not a perfect circle.
(D) Earth's axis precesses over a 23,000 year cycle.

[*] timeanddate.com/eclipse/lunar/2015-september-28.
[**] eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2015Sep28T.pdf.

Correct answer (highlight to unhide): (B)

When the moon is full and the moon's orbit is seen edge-on from the sun's perspective, there will be a total eclipse as the moon passes completely behind Earth, in Earth's umbral shadow. However, the moon's orbit will typically change its tilt such the subsequent full moon will no longer pass directly behind Earth, being either too high or low to pass into Earth's umbral shadow, making it just a regular full moon instead of a total lunar eclipse.

Response (A) explains why the near side of the moon appears to be constant; response (C) explains why some solar eclipses are annular rather than total; and response (D) is the reason why Polaris will not always be the pole star.

Section 70158
Exam code: quiz02s5Sz
(A) : 3 students
(B) : 25 students
(C) : 13 students
(D) : 1 student

Success level: 63% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.83

Section 70160
Exam code: quiz02Nnz2
(A) : 0 students
(B) : 16 students
(C) : 13 students
(D) : 0 students

Success level: 57% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75

Astronomy quiz question: August 2017 partial/total solar eclipse in St. Louis, MO

Astronomy 210 Quiz 2, spring semester 2013
Cuesta College, San Luis Obispo, CA

In August 2017, observers in different neighborhoods of St. Louis, MO will either observe a partial solar eclipse or a total solar eclipse[*], depending on whether they are located in the moon's __________ or __________, respectively.
(A) negative shadow; penumbra.
(B) negative shadow; umbra.
(C) penumbra; negative shadow.
(D) penumbra; umbra.
(E) umbra; negative shadow.
(F) umbra; penumbra.

[*] eclipse2017.org/2017/maps/cities/STL.htm.

Correct answer: (D)

An observer in the moon's penumbra will see a partial solar eclipse, while an observer in the moon's umbra will see a total solar eclipse. (The "negative shadow" refers to the antumbra of the moon.)

Section 30674
Exam code: quiz03Ne3v
(A) : 4 students
(B) : 4 students
(C) : 0 students
(D) : 14 students
(E) : 1 student
(F) : 7 students
(No response: 1 student)

Success level: 47% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.23

Section 30676
Exam code: quiz02Sl1v
(A) : 5 students
(B) : 4 students
(C) : 8 students
(D) : 15 students
(E) : 5 students
(F) : 5 students

Success level: 41% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73

Presentation: eclipses

Cats casting shadows. Eh, this looks Photoshopped. How can you tell? What clues do you look for? As we'll see, it's not just the shadows cast by objects that are important, but where we are located relative to these shadows.

In the previous presentation, we discussed the motion and cycles of the moon--specifically lunar phases--and here we'll complete our discussion of the moon with eclipses.

Just a public service announcement about watching solar eclipses--make sure you are not looking directly at the sun with the unprotected eye. Either project an image of the sun using a pinhole, binoculars, or telescope...

...or use filters specifically labeled for observing the sun. My dog can practice safe solar eclipse viewing, and so should you.

First, the boring but necessary terminology.

Make sure you can distinguish between very similar terms:

• full and new moon (well, this should be self-explanatory).
• lunar eclipse and solar eclipse (light from the sun that would illuminate the full moon is blocked by Earth; direct light from the sun that would reach Earth is blocked by the moon).
• partial, total, and annular eclipse (sun or moon partially or totally covered/darkened, respectively; annular refers to an "annulus" or "little ring," where the moon is centered on the sun, but does not completely cover the sun).

Let's observe a simulation of a total lunar eclipse in April 14, 2014, as seen from the perspective of the sun. Note that Earth blocks light to the moon. Where would you have to be located (on Earth) to observe this total lunar eclipse? Where on Earth would observers not be able to see this total lunar eclipse? What phase is the moon in during this total lunar eclipse? (Why is there not a total lunar eclipse during every full moon?) (Video link: "1-5-140415-Lunar.mov.")

Here's a simulation of a total solar eclipse from July 11, 1991, again seen from the perspective of the sun, where the moon blocks light to Earth (casting a much smaller shadow). Where would you have to be located (on Earth) to observe this total solar eclipse? Where on Earth would observers not be able to see this total solar eclipse? What phase is the moon in during this total solar eclipse? (Why is there not a total solar eclipse during every new moon?) (Video link: "1-5-910711-Solar.mov.")

Time to do a picto-quiz--you'll be shown a picture or movie clip of the moon and/or sun (assume that each of these situations is the maximum extent of something being shadowed or blocked), and then be prompted with possible responses. At that point, if you know the correct answer, shout it out--because yes, the loudest answer is the most correct answer...

Is this a solar or lunar eclipse, or not an eclipse at all? Is this eclipse partial, total, or annular?

Is this a solar or lunar eclipse, or not an eclipse at all? Is this eclipse partial, total, or annular?

Is this a solar or lunar eclipse, or not an eclipse at all? Is this eclipse partial, total, or annular?

Is this a solar or lunar eclipse, or not an eclipse at all? Is this eclipse partial, total, or annular?

Is this a solar or lunar eclipse, or not an eclipse at all? Is this eclipse partial, total, or annular?

Is this a solar or lunar eclipse, or not an eclipse at all? How do you know that this is not an eclipse? What phase is this moon?

One more slide, for you Twihards--which team are you on? (Why is there no Team Bella?)

Second, let's consider why not every full moon is a lunar eclipse, and not every new moon is a solar eclipse.

This is a to-scale simulation of the moon revolving around Earth, while Earth revolves around the sun, as seen from the perspective of the sun. A lot goes on simultaneously, so just watch this and observe the different types of motions. After we discuss what details we should be looking for, we'll run this simulation again. (Video link: "1-5-Linesofnodes.mov.")

Note that the orbit of the moon is tilted, and the bright part is closest to us (the sun) and tilted downwards, while the dim part is farthest away from us, and tilted upwards. Which phase is the moon in right now? How do you know that an eclipse is not occurring right now? How do you know this?

The tilt of the moon's orbit changes slowly over time. Which phase is the moon in right now? How do you know that an eclipse is not occurring right now? How do you know this?

Generally an eclipse can happen only if (1) the moon is either new or full, and (2) the moon's orbit is aligned edge-on. Our previous two examples had the right phase, but wrong orbit; then the right orbit, but the wrong phase. Now we have both the right phase (although it is not clear whether it is new or full) and the right orbit (edge-on), and some type of eclipse (whether solar or lunar) is occurring right now. The timing between the moon phase and slowly changing moon orbit is crucial, and if the timing between these two cycles is not perfect (as it usually isn't), this is why there is not a solar or lunar eclipse every new or full moon.

Back to our simulation. When an eclipse happens (whether solar or lunar), you all say "now." Synchronize! Approximately how many months lapsed during this time? How many eclipses (whether solar or lunar) occurred during this time?

Let's look at two full moons, and flip between them. One is a (nearly) full moon that is just about to undergo a total lunar eclipse, and the other is a full moon that will not undergo any type of lunar eclipse. Can you determine the difference(s) between these two full moons?

Remember that the reason a lunar eclipse does not occur every full moon is that the orbit of the moon is usually tilted not edge-on, but too high or too low. Notice that the "Not to be eclipsed" moon has a slight shadow on the bottom, meaning that its orbit is too high, while the "To be eclipsed" moon has sharp edges at both top and bottom, meaning that its orbit is edge-on and will pass directly behind Earth for a total lunar eclipse. Next time just before the moon is completely full, take a careful look at the top and bottom edges of the moon (you will probably need binoculars or a telescope). If you see a slight ragged edge at the top or bottom, don't get too excited, as a total lunar eclipse is not impending.

In this promotional photograph for a certain obscure TV show from a few years ago, is it plausible that all these actors and actresses were present at in the studio at the same time? How do you know? What clues do you look for?

In the subsequent in-class activity, we'll be looking carefully at the different "shadow zones" cast by either the moon or Earth, and what would be observed if were located in each of these zones: umbra, penumbra, and antumbra (not a common term, we'll refer to the antumbra as the "negative shadow").

Astronomy quiz question: total solar eclipse location

Astronomy 210 Quiz 2, spring semester 2012
Cuesta College, San Luis Obispo, CA

An observer in San Luis Obispo, CA is watching a total solar eclipse. During this eclipse, the observer is located in:
(A) the moon's umbra.
(B) the moon's penumbra.
(C) the moon's negative shadow.
(D) Earth's umbra.
(E) Earth's penumbra.

Correct answer (highlight to unhide): (A)

For a total solar eclipse, the new moon is between the sun and Earth, blocking light the light from the sun. All observers in the umbra (the "complete" shadow zone) of the moon would have all sunlight blocked from reaching them, and thus they would see a total solar eclipse.

(Response (B) would be for a partial solar eclipse (assuming that is the maximum extent of its progress), response (C) would be for an annular solar eclipse. Responses (D) and (E) correspond to the location of the moon during a total and partial lunar eclipse, respectively.)

Section 30676
Exam code: quiz02SnT4
(A) : 20 students
(B) : 4 students
(C) : 7 students
(D) : 9 students
(E) : 1 student
(No response : 1 student)

Success level: 52% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.57

Astronomy quiz question: in the moon's umbra

Astronomy 210 Quiz 3, fall semester 2011
Cuesta College, San Luis Obispo, CA

What type of eclipse is seen by an observer on the side of Earth facing the sun, located in the umbra of the moon?
(A) An annular solar eclipse.
(B) A partial solar eclipse.
(C) A total solar eclipse.
(D) A total lunar eclipse.
(E) A partial lunar eclipse.

Correct answer: (C).

Section 70158
Exam code: quiz03sO1L
(A) : 2 students
(B) : 6 students
(C) : 17 students
(D) : 11 students
(E) : 0 students

Success level: 52% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.52

Section 70160
Exam code: quiz03N1rE
(A) : 4 students
(B) : 5 students
(C) : 14 students
(D) : 1 students
(E) : 3 students

Success level: 54% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.86

Astronomy midterm question: simultaneous total lunar and total solar eclipses?

Astronomy 210 Midterm 1, Spring Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] Consider the following excerpt regarding viewing total lunar and solar eclipses:

On July 6, 1982, a woman telephoned a radio show that had invited people to give their impressions of the total lunar eclipse then in progress. She said: 'We're seeing this total eclipse of the moon right now on our side of the world. Does that mean that at this same moment the people on the other side of the world are seeing a total eclipse of the sun?'"
—Guy Ottewell, Astronomical Calendar 2010, Universal Workshop, Raynham, MA, 2009, p. 43.

Decide whether seeing a total eclipse of the sun "at this same moment" is plausible or implausible. Support your answer using a diagram showing the positions of the sun, moon, and Earth.

Solution and grading rubric:

• p = 20/20:
  Correct. Draws a correct diagram of a total lunar eclipse, where the moon is on the other side of Earth than the sun; and since the moon must be on the same side of Earth as the sun for there to be a total solar eclipse, it is implausible that observers anywhere on Earth can observe a total solar eclipse simultaneously with a total lunar eclipse. May also illustrate and argue the converse argument, when a total solar eclipse is occuring a total lunar eclipse cannot be simultaneously observed.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Diagram is problematic (misalignment of sun-Earth-moon line), but essential argument that the moon cannot be at two different locations on either side of Earth correct.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Diagram missing, but essential argument correct, or vice versa.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Argument based on timing of time zones, size of moon's umbral spot, or improbable sun-Earth-moon diagrams.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 30674
p: 36 students
r: 1 student
t: 1 student
v: 6 students
x: 0 students
y: 0 students
z: 0 students

Section 30676
p: 62 students
r: 6 students
t: 23 students
v: 13 students
x: 13 students
y: 1 student
z: 3 students

A sample "p" response (from student 1802):

Another sample "p" response (from student 7129), lamenting the fact that Earth does not have two moons:

Another sample "p" response (from student 2425):

A sample "v" response (from student 9696), with two Earths?

Astronomy quiz question: annular/total solar eclipses

Astronomy 210 Quiz 2, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

Why are some solar eclipses annular rather than total?
(A) The orbit of the moon around Earth is tilted with respect to the orbit of Earth around the sun.
(B) The orbit of the moon not a perfect circle, but is an ellipse.
(C) The moon rotates such that it always keeps the same side facing Earth.
(D) The direction of Earth's axis precesses over a 23,000 year cycle.

Correct answer: (B)

During a total solar eclipse, the moon blocks the entire sun, when observed from within the umbral shadow spot on Earth. However, due to the elliptical orbit of the moon, it may be unable to completely block the entire sun as seen from Earth, due to its distance from Earth being too far.

Response (A) explains why a total solar eclipse does not occur every time the moon is new. Response (C) explains why the near side of the moon is constant; response (D) is the reason why Polaris will not always be the pole star.

Section 70160
(A) : 25 students
(B) : 16 students
(C) : 0 students
(D) : 1 student

Success level: 43% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.82