MUSE  EarthMoonSun Dynamics  Course Overview and Materials  Building the EMS Model  Course Material 2E: Eclipses  Instructional Notes 

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INSTRUCTIONAL NOTES Intended Learning Outcomes Skills and Nature of Science
Lunar eclipses
Solar eclipses
Supplies
Time Frame and Sequence This material will take four days to complete. It starts with a pretest assessment of students’ prior knowledge of eclipses. Next, students examine eclipse data that has been compiled over several years, noting patterns in both eclipse type and frequency. The lessons continue as students extend their EMS model to account for these solar and lunar eclipse patterns. Day 1 — Students’ Prior Knowledge Have students take the eclipse pretest. Follow this with a class discussion during which students should share their ideas about eclipses. Have one student look up the word "eclipse" in the dictionary and share it with the class. It will likely read something like, "the partial or complete obscuring, relative to a designated observer, of one body by another". Write it on the board. Ask students if this definition makes sense to them. Help students clarify this definition by breaking it down; for example ask students the meaning of some of the individual terms such as partial, complete, obscuring etc. Next ask a few students to use their bodies as props to demonstrate an eclipse. Point out that from the observer’s perspective, if the larger student is in front, then this can be thought of as a complete (total) eclipse as opposed to having the smaller student in front which would result in a partial eclipse. Now students should have a pretty good idea of what an eclipse is. Continue by writing the terms "lunar" and "solar" on the board. Students will likely be able to predict that lunar means Moonrelated and solar means Sunrelated. Have students work in groups for about ten minutes to share their ideas about the following four questions. Encourage groups to make use of props.
Have students reconvene as a class and ask for volunteers to demonstrate their solar eclipse ideas. While a group of students is demonstrating, write on the board the order of the bodies, as they mention them, that are involved in a solar eclipse (Earth, Moon, Sun). Have another group of students continue by demonstrating the positions of the relevant bodies (Moon, Earth, Sun) involved in a lunar eclipse. Again, note this order of bodies on the board as students mention them. Next, move the Moon prop students are using to the other side of the Sun (such that the order is now Earth, Sun, Moon) and ask students if a lunar eclipse would result if the Moon were in this position. Students should respond by saying that such a configuration of the Earth, Sun and Moon is not possible because the Moon orbits the Earth as it orbits the Sun, and therefore the Earth and Moon can never be separated by the Sun. From here students should be able to determine the Moon phase associated with each type of eclipse and should be aware that the Moon is new during a solar eclipse and full during a lunar eclipse. Note these connections on the board as well. Demonstrate these phases with props and a light source if necessary for your students to make the connection between type of eclipse and Moon phases. Eclipse Data & Patterns Ask students what they usually examine next when developing their understanding of a phenomenon. They should respond "data". Give students a sheet of eclipse data that spans ~ five years and ask them what they should do next. Given their prior experiences with the Black Box (Material 1D) and each celestial phenomenon studied thus far (Materials 2A2D), students should note that their next task will be to identify patterns in this data. Remind students that they are continuing to construct the same EMS model which describes interactions between the Earth, Moon, and Sun and the motions of these bodies. Thus, their examination of the data for eclipses will require them to focus on these same bodies and motions. Individually, have students examine the data and identify a variety of patterns. If time remains, have students share the data patterns they are able to identify with their neighbors. For homework, students should continue to examine the eclipse data for additional patterns. Day 2 — Eclipse Data Patterns Have students get in their groups and share the eclipse data patterns they have noticed. While in groups, encourage students to focus on patterns in a number of different relationships — between one solar eclipse and the next, between one lunar eclipse and the next, and between a solar and the next lunar eclipse. After reconvening as a class, ask students to share the data patterns they have identified as well as evidence from the data that supports these generalizations. This will likely be a lively discussion with a number of students contributing pieces that will ultimately result in identification of a fairly complex overall pattern. For example, individual students may offer the following comments:
At this point in the discussion, ask students what the data tells them about the shortest and longest time that elapses between eclipses. They should respond, "14 days and 6 months". Point out that unlike the Moon phase data that students gathered on their own earlier in this unit, it would be impossible for them to gather eclipse data and use it in class this year as the patterns in eclipses occur over a much longer period of time. Predictive Power Ask students if they have enough information to predict eclipses. Do some predicting for eclipses that will occur during the next year on the eclipse data sheet. After students have made their predictions, give them the actual data for the eclipses that year. Ask students if being able to predict also allows them to explain the phenomenon. For example, do you know why eclipses happen as a result of being able to predict their occurrence? Connect back to the students’ Black Box (Material 1D) predictions to emphasize that their predictions in that instance did not tell them what was inside the box — why/how the predicted data arose. Explaining the Phenomenon of Eclipses Remind students about how relatively simple the beginning phenomenon of day/night was and how they are continuing to use the same EMS model to account for more complex phenomena. Consider taking a moment to actually look back at some of their earlier POM charts to reinforce this point. Tell students that their current task is to explain how the Earth, Moon and Sun interact in order for eclipses to occur. The question is why do we have eclipses alternating and occurring ~14 days and ~6 months apart? Consider writing "14 days" with different units such as 1/2 month or two weeks if your students find this more inviting. Remind students that they have already noted that the same bodies (Earth, Moon and Sun) are involved with the phenomenon of eclipses as with other phenomena explainable by their EMS model. Identifying the relevant motions will be more difficult. Assist students by reviewing the motions that they already know (from their EMS model summary chart) are occurring within the EarthMoonSun system. For example, the Moon, taking a month to orbit the Earth, is a motion students established earlier in the curriculum (during Material 2D) and thus their model must remain consistent with it. Have students get into groups and discuss how to account for the eclipse data patterns they identified earlier in today’s class. The key aspect is likely to be the motions of the bodies involved and in particular, the interaction of their orbits. Darken the room and have either one classroom light source suspended from the ceiling or group light sources (flashlights) available. Students should make use of props and continue to think about these motions for homework. Day 3 — Explaining the Phenomenon of Eclipses: Eclipse POM Chart Since students had some group time to discuss their models yesterday, start class by handing out a blank eclipse POM chart. Ask students to review what they already know and have them fill this information in on the chart. This chart is not meant to be used as a worksheet, so it is important that students have an opportunity to discuss their ideas before using it. The POM chart is meant as a guide to structure students’ ideas once they have had a chance to discuss them. Students should contribute the following to the POM chart at this point:
Write the above student contributions on the board and ask students what the basis is for their description of this phenomenon. They should understand that their description is based on data. Next, ask students what they think might account for the phenomenon of eclipses. Frequently, students will hold one or both of the following ideas:
As students share and demonstrate their ideas, point out – through guiding questions whenever possible – how their models are or are not consistent with their current EMS model and the body of data they have examined so far. You may also want to help students test their models by suggesting "experiments." For example, a student who thinks that the Earth's tilt causes eclipses can be encouraged to use props to demonstrate the Earth, Moon, and Sun positions during an eclipse with and without a tilted Earth. This demonstration will show that eclipses occur whether or not the Earth is tilted. During and immediately after this discussion, many students will probably have initial models  that is, they will suspect that either the Earth's orbital tilt or the Moon's orbital tilt is important in causing eclipses, but will not be able to demonstrate the cause  effect relationship at this point. They may be able to account for some, but not all, of the data, or they may be struggling with inconsistencies between their models and prior knowledge. Offer students the use of another prop before they begin working in their groups. This new prop is meant to represent the Moon’s orbit of the Earth and can be made out of pipe cleaners in the form of a circle with an attached small Styrofoam ball to represent the Moon. This will help students think of the Moon’s orbit of the Earth as a plane (an object), which seems to be a key aspect in understanding eclipses. Have students work in their groups to continue thinking about how their model of the Earth, Moon and Sun can account for their eclipse data. Students may add to their eclipse POM during this time.Reconvene as a class and ask students to remind each other about the three criteria by which they judge models (explanatory power, predictive ability and consistency with what they already know about the way the world works). Ask for volunteers to share their models to explain eclipses. While sharing with the entire class, use enlarged versions of the student groups’ props, for example use a classroom Earth globe along with a hula hoop with a large attached Styrofoam ball instead of the inflatable Earth globes and pipe cleaner Moon orbits used by the individual groups. One powerful potential model – which is an extension of the notion that the Moon's orbit around Earth is tilted with respect to the equator – is a fluctuating Moon orbit model. In this model, students will propose that the tilt of the Moon's orbit around the Earth is in constant, periodic flux such that the Moon aligns favorably for eclipses twice each calendar year. You'll note that this model is powerful because it can account for the students' data. However, you can refute the model by asking the students what they know about Newton’s laws of motion. Most upper middle school students will have learned about Newton's laws and some will recall that if an object (the Moon in this case) is moving it needs to be acted on by a force in order to alter that motion. A model that states that the angle of the Moon's orbit around Earth is constantly fluctuating is inconsistent with this basic tenet of physical science. By the end of this discussion of eclipse models, students should understand that as the Moon orbits the Earth (which is simultaneously orbiting the Sun), the Moon is sometimes (at two nodes) in planar alignment with the Earth and Sun, and these are the only locations that allow for eclipses to occur. At other points along the Earth’s orbit of the Sun, such a planar alignment does not occur due to the tilt of the Moon's orbit. This is a challenging concept for students to understand, and it is entirely possible that no student group will propose a complete model. It has been our experience that explanation of eclipses through modeling requires more direct instruction than any other phenomenon in this curriculum. Thus, having established through their own exploration that the Moon's tilt is an important aspect of the EMS model pertaining to eclipses, you may need to guide the students to simulate a yearlong series of Moon/Earth orbits during one Earth/Sun orbit and note the interactions between these orbits at the nodes. Once students are able to visualize the consequences of a tilted Moon orbit (that is constant and does NOT fluctuate), most will be able to understand the cause of eclipse phenomena. Students should complete their eclipse POM for homework (motions, explanation and diagram sections). Day 4 — Review Eclipse Phenomenon Review your class discussion from yesterday and have students demonstrate with props how the EMS model can now account for the phenomenon of eclipses. Give students an opportunity to ask questions before having them share their eclipse POMs with their fellow group members. Students should discuss their eclipse models and modify their eclipse POMs while in their groups. Student Ideas and Teaching Strategies Day 1 — Students’ Prior Knowledge When a group of students is demonstrating their eclipse ideas, take care to note on the board what it is they are saying, rather than paraphrasing. Students should notice the flaw in the arrangement of celestial bodies when you move the Moon to the opposite side of the Sun from where the Earth is located if they understand that the Moon is always in the process of orbiting the Earth, thus the Sun can never be between these two bodies. Eclipse Data Patterns Students will likely be able to easily identify the objects involved in the phenomenon of eclipses. They are likely to find the task of identification of patterns in the eclipse data to be much more challenging. Continue to encourage students to identify more patterns even after they have successfully identified some. This data has a number of patterns in it for students to notice. Day 2 — Eclipse Data Patterns While exploring data patterns, individual students may offer the following comments:
Predictive Power Students will likely be able to predict eclipses with a great deal of accuracy, but helping them to see the difference between a prediction and an explanation here will point out to them that people can predict without ever having an understanding of the cause of a phenomenon. Explaining the Phenomenon of Eclipses If it helps your students, consider writing the eclipse data patterns with a variety of units, for example: 14 days can also be written as two weeks or ~ 1/2 month. Being able to explain the phenomenon of eclipses is a very challenging task, so reminding students that they have come a long way with the explanatory power of the same EMS model may provide them with a context for their struggles. They are not really learning something brand new with the phenomenon of eclipses, but rather they are extending a familiar model of the Earth, Moon and Sun to account for even more natural events. Day 3 — Explaining the Phenomenon of Eclipses The POM chart is meant as a guide to structure students’ ideas once they have had a chance to discuss them, thus it is important that it be used only after students have had significant time to discuss their ideas. As a class, when you are completing the POM chart, students should have little difficulty contributing the following aspects:
Students are likely to think that the Earth’s tilt and/or the tilt of the Moon’s orbit may play a role in the phenomenon of eclipses. By asking students to demonstrate or say more about how they see these aspects impacting eclipses, it is likely that they will see that their ideas may not completely match the data patterns they have already identified or that some of the assumptions of their models violate accepted tenets of physics. Providing students with an additional prop that will help them see the Moon’s orbit of the Earth – and by extension, the Earth's orbit around the Sun – as a plane or ‘object’ can significantly assist them as they continue to probe the role the orbit’s tilt plays in the phenomenon of eclipses. When students demonstrate the Moon’s orbit of the Earth, they can easily, and often unintentionally, vary the angle of this orbit. Such unintentional variations become more difficult for students to make when the Moon’s orbit is thought of as an object or plane and the students have a steady prop with which to visualize this phenomenon. The hula hoop or pipe cleaners can allow them to better isolate the ‘tilt’ feature of the Moon's orbit and examine its role in the phenomenon of eclipses. 
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