Alter component of model and predict (cause to effect reasoning).

Transcription

1 2A: Day/Night and Sunrise/Sunset: Instructional Notes Intended Learning Outcomes Create models to account for phenomena. Assess models for data fit and consistency. Alter component of model and predict (cause to effect reasoning). Make diagrams. Use props to create or communicate models. Understand that day and night are caused by the Earth s rotation on its axis ("spin"). Understand that one Earth rotation takes 24 hours, therefore we have 24 hour days: roughly 12 hours of darkness when we are facing away from the Sun and 12 hours of light when we are facing toward the Sun. Understand that the Earth spins counterclockwise, thus the Sun appears to rise in the east and set in the west. Understand how to correlate time of day with position of the Earth relative to the Sun. Supplies Light source (1 / classroom) Inflatable Globes are available through: The Globe Corner Bookstore orders@gcb.com FAX: Toll Free: Mail: GCB Order Department 46 Station Street Brookline, MA POM charts (2 / student) Time Frame & Sequence Completion of this material will take about three days. It will start with a discussion about students prior knowledge on Day 1 and continue with the construction of the EMS model (to account for day and night, sunrise and sunset) on Day 2. Correlation of time of day with

2 Earth/Sun position and the extension questions related to rise and set phenomena will be the focus of Day 3. DAY 1 Introduce the activity by reminding students about the Moon phase observations that they have been making and note that they will now begin to identify patterns in that data and eventually create models to account for related Earth-Moon-Sun phenomena. To learn more about students initial ideas and to let students think more about these ideas, give students the Day/Night pretest. The pretest requires students to give a complete explanation in their own words of why they think we experience day and night. In addition to their written explanation, they should draw and label a diagram that illustrates their ideas. Next, ask students to share their explanation for day/night by drawing diagrams on the board. Alternatively, they may use a globe to represent the Earth and a lamp to represent the Sun and demonstrate why they think we have day and night. Once the students have shared their initial ideas about day and night, remind them that you are aware that these ideas are probably not new to them. However, in the upcoming unit, it will be important for the whole class to agree on a way of talking about what they know. Thus, it is useful to begin learning about how to communicate ideas when discussing something fairly familiar like day and night. Then return to their explanations that they shared on the board or through demonstration. Ask someone in the class to summarize the ideas about day and night and while he/she does this, go to the board and take "notes." Your notes should be in the form of a running list and include all the pertinent information for filling in a POM (Phenomena-Objects-Motions) chart: the phenomenon to be explained, and the objects and motions that are involved. For example, while your student talks, write down items such as "day and night" "24 hours" "Earth spins" "Sun s light" etc. as he/she says them. Now you are ready to introduce the POM to the students. Next, put a copy of a blank POM on the overhead and pass out one to each student. Tell students that this will be one format that they will use to communicate their EMS model during the next several weeks, as they expand their model to account for more and more phenomena. Then use the students own ideas (which you have noted on the board) to help them fill in the chart. In going over the POM, be sure to help students see how it contains the same information communicated differently as their own explanations for day and night. Finally, pass out another blank POM and ask students to fill in the question, "Why does the Sun rise in the east and set in the west?" Students can have the rest of the hour to work on this task (working in small groups with their props) and should complete the rest for homework. A complete POM for the Sun rising in the east and setting in the west is included in the student activities section. DAY 2 The focus for today will be discussing why we observe the Sun rise and set as we do. This will take about minutes. Begin by asking your students what they have observed about the Sun rising and setting. Help students to establish that the Sun generally rises in the east and sets in the west you may have some students who already know this information and others who might need prompting to think about what they observe first thing in the morning or as they go home in the afternoon, etc. Ask the students which objects and motions are involved in the Sun rising in the east and setting in the west. Students should work in groups to figure this out. After about minutes of small group work, a few groups can share their ideas with the class as a demonstration. As the students demonstrate, ask them to note the direction in which the Earth rotates (students should demonstrate a west to east or counterclockwise motion or at least

3 know that this is necessary to observe the Sun rise in the east). You may find it helpful to establish a convention for discussing the direction of rotation from an outer space perspective: i.e. assume that you are in space looking down at the north pole and note that the Earth rotates counterclockwise. In space, "east" and "west" are not adequately referenced and so are not a useful convention for establishing direction of rotation. After the students have shared their models, revisit the POM that they completed for homework and add this new information for a more complete POM (new phenomenon: east to west apparent motion of the Sun; new motion: west to east counterclockwise rotation of the Earth). Hand out the Day/Night extension questions. Allow about minutes for students to get into groups to start their work on these questions and ask them to complete the questions before tomorrow. The questions require students to alter a component of their model (such as the motion of one of the objects) and predict the resultant phenomena (cause to effect reasoning). Day 3 Ask the class to discuss how they approached the extension questions and compare their answers. You may consider giving students 5-10 minutes to get in their groups to share their ideas prior to reconvening as a whole class. Have students identify the component of the model that is changed the Earth, the Sun or the motion of one of these objects and how it results in a change in the phenomenon observed. Encourage students, either individually or as a group, to use props to represent the Sun and Earth to demonstrate their ideas to the class. Spend the remaining time asking students to use the props to demonstrate the correlation between time of day and position of the Earth relative to the Sun. Understanding this relationship is important for students ability to complete material 2B: Moonrise & Moonset. Give each small group of students two or three times that they will need to demonstrate (for example: sunrise, noon, 3PM, etc.). After approximately 10 minutes, ask each group to demonstrate the positions of the Earth and Sun at each of their assigned times. Note that they will have to indicate where on Earth a person is standing at each of these times. Student Ideas and Teaching Strategies Day 1: Pretest and Day/Night Discussion Some common student ideas that may surface through the Day/Night pretest include the following: Before instruction, most students will already know that sunlight hits the Earth to create day, and when it doesn t hit the Earth, it is night. The Earth spins, so we get both day and night. A few may invoke a geocentric view of the solar system, suggesting that the Sun actually orbits the Earth daily, causing the phenomenon of day and night. It is uncommon to have students voice this idea during a class discussion. However, if such a model does emerge in discussion, you may ask the class as a whole to respond to the idea or you may ask the student in question how long it takes the Sun to orbit the Earth. This question generally reminds students that it takes the Earth a year to complete an orbit (albeit an Earth orbit, not a "solar" one) and produces enough dissatisfaction with the geocentric view to enable you to move forward with the heliocentric model. Students commonly provide more information than is necessary to explain the phenomenon or observations in question. For example, some may include in their explanations that the Earth orbits the Sun or the Moon orbits the Earth. However, this information is not necessary to account for the phenomenon of day and night. You want to address this by asking

4 students to use props to explain why we experience day and night. Then ask the students to eliminate the Moon or the Earth s orbit from their explanation and note whether or not their model still accounts for day and night. Students may also want to bring in other information not directly related to day and night. For example, students will frequently note that day and night are dependent upon the seasons correctly noticing that daylength varies with seasons, but incorrectly confusing the general phenomenon of day and night with the specific length of each day. To focus the students thinking only on the day and night phenomenon, ask whether we experience day and night in summer, spring, fall, and winter. Most students will concede that, although the specific length of day changes with the seasons, the regularity of 24-hour periods of dark and light does not. Note also that some students will be curious about the day and night phenomenon in polar areas, where the sun either doesn t rise or doesn t set for long periods of time during particular seasons. You will probably want to table this question add it to the list of class questions until the discussion of seasons, where the Earth s tilt and its orbit will be discussed in greater detail. Our students have been receptive to this honest way of dealing with their questions and are willing to postpone discussions of particular issues as long as they are assured that they will return to them eventually. Introducing the POM Charts When you introduce the POM as a way for students to communicate their ideas to one another, be sure to point out that the students own ideas and the information on the POM are the same. The POM merely organizes their ideas in a way that can be used over and over again throughout the EMS unit. Because the POM charts are used extensively, it is important at the beginning to build students confidence about using them: it is not desirable for students to view the POM charts as worksheets that need to be filled out in a rote manner. Rather, the POMs are a way for students to focus their ideas and organize their explanations. You can assist students in making this connection by asking a class member to use the props representing the Sun and Earth to demonstrate day and night and take notes of his/her ideas as this occurs. Then work with the class to fill out the Day/Night POM, showing students how to begin with their ideas and "translate" them into the form called for on the POM. For example, as the student says that he/she will explain how we experience day and night every 24 hours, you might write "every 24 hours we have day and night" on the board or under the "phenomenon" column in a blank POM. As the student uses props representing the Sun and Earth, you can write "Sun" and "Earth" on the board. As the student spins the globe, you can write, "Earth spins (or rotates) on its axis." The "motions" part of the POM will probably be the most difficult because students need to decide what is important and what is not. Students have a tendency to try to include every object and motion in their model rather than focusing on the relevant objects and motions for the phenomenon at hand. To clarify, ask if the Moon orbiting the Earth has any effect on day and night since many students models of day/night will include this component. Students should conclude that day and night occur independently of the Moon. In fact, they will probably have some evidence of this already, as they have been noting how the Moon changes phase and is visible at different times of the day/night. Regardless of these Moon phenomena, day and night continue to occur. Student diagrams and their written explanations often do not match. This may be due to limited writing ability among some students. You may want students to talk as well as demonstrate to ascertain which idea the student is trying to express. Teachers should work with students to clarify how their ideas are expressed in words. This is one of the reasons that we emphasize student use of demonstration in our curriculum Day 2: Sun Rise and Sun Set

5 When you begin the discussion of sunrise and sunset direction, you may need to assist students in orienting themselves according to compass directions. Consider connecting some pertinent local landmarks to the directions of East and West, etc. Changing perspective from being on Earth to looking at Earth from space will be a challenge for most students. Moreover, students will have practice taking different perspectives throughout the EMS unit. Thus, it is a good idea to make this skill explicit from the beginning, while discussing a convention for naming the direction of Earth s spin (counterclockwise if viewed from outer space looking down on the North pole). You can also note that on Earth, the Sun appears to move (rise and set), but from a space perspective, it is the Earth that is in motion. Day 3: Extension Questions For the extension questions, students will struggle most with questions like "How would day and night change if Earth s orbit were two times closer to the Sun?," because they have difficulty filtering out relevant from irrelevant information. In questions such as the one above, the phenomenon in question remains unchanged because the motion or object that has been altered is not involved in that particular phenomenon. Having students use props to represent the Sun, Moon, and Earth can help them see what is relevant and what is not and is one strategy to deal with this challenge. In the example above, the teacher or a student could position the Earth (globe) closer to the Sun (lamp) while continuing to rotate the Earth every "24 hours" and note whether the new orbit has any effect on the phenomenon of day and night. Time of Day Correlating the position of the Earth (relative to the Sun) with a specific time of day is usually challenging for students and may require more time than just the last part of Day 3. Note, however, that it is important for students to grasp this idea before moving on to Material 2B: Moon Rise & Set. Their study of Moon rise and set phenomena will begin with a close look at moonrise times over a two-week period. During this material, it will be necessary for them to relate the pattern in moonrise times to the Moon s position relative to the Earth, and therefore the concepts that they wrestle with in this lesson are drawn upon immediately in the next. During this lesson, it is helpful to assume that sunrise is at 6AM and sunset at 6PM. Also assume that the Sun is highest in the sky at noon (12PM). Students will have to assume a fixed position on the Earth in order to demonstrate Earth position at a given time of day. Consequently, it is helpful to have Earth globes that have the continents already marked on them. In this case, students can assume that they are located in their own hometown. If you are using other spheres (such as Styrofoam balls) to represent the Earth, provide each group with a pushpin to mark a fixed position on Earth. Assume the pin represents their position during this lesson. Students frequently mistake the noon position for sunrise: that is, they think that when their fixed position on Earth is directly facing the Sun, that is the first time the Sun is visible from that location (and is therefore sunrise). This position (directly facing the Sun) is actually noon, or the Sun s highest point in the sky. If students are struggling with this, ask them to use their own bodies to represent Earth rather than spheres or globes. Ask them to extend their arms fully to each side. Now ask them to stand so that one of their arms is directly pointing at the Sun (light source) while their eyes are at a 90 angle from the Sun. Can they see the Sun out of the corners of their eyes? Since they are able to see the Sun in this position, this represents sunrise. Then ask them to rotate 90 such that their eyes are directly facing the light source. This position represents noon. Rotating another 90 such that their opposite arm is directly pointing at the Sun represents the position of the Earth at sunset. Note that in this demonstration the students eyes represent a fixed position on Earth, analogous to their hometown on a globe or the pushpin on a Styrofoam

6 ball.