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MUSE | Earth-Moon-Sun Dynamics | Course Overview and Materials | Building the EMS Model | Course Material 2C: Face of the Moon | Instructional Notes


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course material 2D: Phases of the Moon


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Intended Learning Outcomes
  • Recognize data patterns.

  • Create models to account for phenomena.

  • Assess models for data fit and consistency.

  • Revise models based on additional data (model extension) / effect to cause reasoning.

  • Identify components of model.

  • Use of classroom norms (basic interpersonal skills).

  • Make observations.

  • Make diagrams.

  • Use props to create or communicate model.

  • Understand that models are ideas that scientists use to explain patterns they see in the world. In other words models are explanations that scientists develop to explain natural phenomena.

  • Understand that models are judged to be acceptable or not based on how well they explain the data, how consistent they are with other knowledge (or realistic), and how well they can be used to predict.

  • Understand that on any given night/day, every place on the Earth sees the same face of the Moon.

  • Understand that we always see the same face of the Moon from Earth because the Moon spins on its axis once for every time it revolves around the Earth (28.5 days).

  • 1 classroom set of high quality pictures of the Moon in its full phase, taken from several global locations (i.e. one each from the southern and northern hemispheres; and one each from a western continent and an eastern continent, etc.) The resources section of this material contains some sites with downloadable images.
  • Styrofoam Moon balls (one/group)
  • Earth globes (one/group)
  • Light source (to represent the Sun) (one/classroom)
  • Blank POM's for each student

Time Frame and Sequence

Completion of this material usually requires only 1 class period. The objective is for students to recognize that only one side of the Moon is visible from Earth and the same side is always visible regardless of the observer's position on Earth. Students will modify their EMS model to account for this phenomenon by adding a motion: the Moon's rotation (or spin) on its axis.

Day 1: Moon Face

Begin class by displaying several pictures of the Moon in its full phase. Include labels that identify both the location and date for each picture. Make sure that your picture set includes photographs taken from each hemisphere and both Eastern and Western continents. You should also vary the time of year during which each picture was taken. Ask the students to look closely at the pictures and note any patterns that they see. Write down their comments on the board. After you've generated this list of patterns, focus the students' attention on the fact that the Moon face is always the same, regardless of where or when you look at it from Earth. Tell the students that they will spend the rest of the period modifying their EMS model to account for this new phenomenon.

Ask students to work in their small research groups to modify their EMS model in order to account for why we always see the same face of the Moon. After about 15 minutes, ask for volunteers to share their models. At this point, there are often two competing models:

  • One model purports that the Moon spins on its own axis very slowly – once per orbit

  • The other model purports that the Moon does not spin on its axis at all.

While students are discussing these tentative models, use the board to keep track of their different ideas. After the initial discussion, ask students what they can agree upon thus far. Generally, they will agree that the objects involved in explaining this phenomenon are the Earth, Moon, and Sun. Write the following on the board:

  • Objects
    • Earth
    • Moon
    • Sun

Next, summarize where there is still disagreement. Usually the students have not come to consensus about whether or not the Moon spins on it axis. Write the following on the board:

  • Motions
    • Moon spins?
    • Moon doesn't spin?
    • Moon orbits Earth (is this important?)

Now have the students return to their small groups and attempt to test these alternative ideas and refine their EMS model. Thus, the students will spend the rest of class focusing on identifying the specific motions involved in this phenomenon. Because it is frequently difficult for students to discern slow movement from no movement, you can suggest strategies for them to simulate these motions. In particular, we have found it helpful for the students to use their own bodies, rather than the Moon balls and globes, as they attempt to recreate the Moon face phenomenon through motion. As the groups work, circulate among them and ask students to demonstrate the phenomenon for you. Help them to distinguish between scenarios where they are spinning very slowly versus not at all (more is said about this in the Student Ideas & Teaching Strategies section below).

After about 15 more minutes, ask the groups to demonstrate their models to the class and hand each student a blank Moon Face POM to complete for homework.

Day 2: Review POM

Begin the second day by spending just a few minutes reviewing the modified EMS model and the Moon Face POM, then begin Material 2D: Moon Phases.

Student Ideas and Teaching Strategies

Moon Pictures

The purpose of showing the students pictures of the Moon taken at different Earth locations and different times of the year is to help them recognize a general pattern: that the Moon's craters are always in the same place from our perspective. Thus, we always see the same face of the Moon regardless of our vantage point on Earth. A variety of pictures will enable students to see that the same Moon face is visible

  • at all times of the year
  • from Northern and Southern hemispheres
  • from Eastern and Western continents

Moreover, if you are able to do so, obtain a few pictures of waxing gibbous Moons as well. The waxing gibbous Moon is full enough to see many of the craters (and thus to compare easily with the full Moon) and is also visible during daylight hours (from about 3 PM until about 3 AM). Thus, these pictures can provide evidence that the same Moon face is also visible at different times of the day.

When you show the students the Moon pictures, remind them that the first thing they did with the Black Box data (in Material 1D) was to identify a pattern. Similarly, they will be seeking a pattern in these Moon photographs. Keep a written record of students' ideas about patterns on the blackboard. Our students have noticed the following patterns in the Moon picture data:

  • the Moons are all in the same phase (full)
  • the Moons are different sizes
  • the Moons vary in color (from white to yellow to orange)
  • the craters are always in the same place

Occasionally, it has been difficult for students to notice the craters. You might prompt them to pay attention to this feature by asking, "Are these all pictures of Earth's Moon? How do you know?" or "Do you think some of these pictures might be of Mars' Moon?" These and other similar questions focus students' attention on the similarities between the pictures rather than their differences. Conclude the discussion by explicitly inferring from the shadow pattern that we are always seeing the same face of the Moon from Earth.

Initial Models

Generally, students readily agree that the objects involved in this phenomenon are the Earth, Moon, and Sun. They struggle to identify the specific motions that give rise to the phenomenon, however. After the initial group modeling work, our students are usually in the process of testing one of three explanatory models:

  1. The Moon is orbiting the Earth in the opposite direction of Earth's rotation. The combination of Earth's rotation and the Moon's orbit gives rise to the same face phenomenon.

  2. The Moon orbits Earth in the same direction as Earth's rotation. The Moon does not spin on its own axis.

  3. The Moon orbits Earth in the same direction as Earth's rotation. The Moon spins very slowly: once per each orbit of Earth. Moreover, the Moon spins in the same direction as its orbit (counterclockwise with respect to a view of the North Pole).

When students present their initial models, keep in mind the criteria for judging explanatory models in science. On this basis alone, the first model above is easily dismissed: the students' own work in Material 2B: Moon Rise & Set demonstrated that the Moon orbits Earth in the same direction as Earth's rotation. Thus, this model is inconsistent with accepted ideas (their EMS model thus far) and must be rejected.

Judging between the other potential models is usually more complicated due to two factors: First, our students have difficulty distinguishing between an object that is very slowly spinning (rotating) and one that is not spinning at all. Second, our students have difficulty learning (and consistently using) the terms 'spin,' 'rotate,' 'orbit,' and 'revolve.' Thus, they frequently have difficulty understanding one another during discussions of their EMS models.

  • We recommend that you use this initial discussion to clarify vocabulary issues. Ask students to demonstrate with their props what 'spin' or 'revolve' look like and allow your class to determine what vocabulary is most useful to convey these key motions. Once you have established a convention for discussing motion, your students will probably be better able to understand one another.
  • As for distinguishing between slow movement and no movement, we suggest several strategies:
    • First, mark the Moon balls with a pen or masking tape in the center of one side. This way the students have a constant reference point on the sphere. Next, mark the top of the balls with a thumb tack. On the top of the tack, draw an arrow. Now as students move the Moon ball around the Earth, they will need to keep the masking tape or pen mark facing the Earth at all times. As they do this, they can note that the arrow on the tack spins relative to the center of the Moon ball. Thus, students can see that the Moon is not only revolving around the Earth, but also rotating around its own center axis.
    • Second, ask students to use their bodies, rather than the spheres, as props. Ask one student to stand in the center of the group and be the Earth. Ask another student to be the Moon. The Moon student should extend her arms and note the direction in which she is pointing. Now, ask this student to continue to point in this direction as she slowly orbits the Earth. Ask the Earth student to describe what side of the Moon he is seeing. This demonstration shows what one's view of the Moon would be if the Moon did NOT spin. Next, ask the Moon student to always keep her face toward the Earth student as she orbits. Note that the Moon student is pointing to various things in the classroom as she orbits–thus, she is spinning. Many students who begin with the second part of this demonstration–simulating a scenario where the same Moon face is always visible–will believe that they did not spin in this situation. Thus, it is important to ask them to do the first part of the demonstration–where they have a fixed reference point to keep them from spinning–first. Demonstrating both scenarios helps to distinguish between slow rotation and no rotation.

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