Teachers TryScience

Investigation 1: The Sun and Your Shadow

Prerequisite:
Students should already understand the Earth’s basic movements in our solar system, including that:

• The Earth completes a full rotation about its axis approximately once a day.
• The Earth completes a revolution around the sun approximately once a year.
• The Earth is rotating while it revolves around the sun, accounting for patterns like day and night.

Materials:

• Chart paper
• Markers
• thermometers
• Meter sticks or measuring tape

Background Information for teacher
Why do we observe day and night? Longer and shorter days at different times of the year? Why does the sun appear to move across the sky? It all comes down to how the Earth moves, relative to the Sun.

The Earth is an oblate spheroid (round and slightly flat at the poles). The Earth completes a full rotation around its axis every day. You can model this by turning around while staying in place- your body moves around a central point that stays constant. As the Earth rotates on its axis, different parts of the earth are facing the sun, accounting for daytime and night time. Revolution is the movement of Earth around the Sun. The Earth orbits, or revolves, around the Sun one time each year, and as it moves through the sky around the Sun, the Earth is in closer (visible) proximity to different stars- this is why we see some stars only at certain times of year.

There is a common misconception that the Earth’s distance from the sun causes seasons, but the reason for our seasons is actually the Earth’s axial tilt. Because the Earth tilted, different parts of the Earth receive more direct sunlight (solar energy) as the Earth revolves around the sun- in other words, when the Earth is at one point in its revolution, a certain portion of the earth is tilted toward the sun; because the tilt remains the same, as the Earth’s position moves around the sun, the portion that is directly receiving solar energy changes. During the northern hemisphere winter months (December-February), the Earth is tilted such that the Southern hemisphere (tropic of Capricorn 23.5 degrees south) receives direct solar energy, and the northern hemisphere receives indirect solar energy. During summer in the northern hemisphere, the Earth is tilted such that the northern hemisphere (tropic of cancer 23.5 degrees north) receives more direct solar energy.

For more information, visit http://www.morehead.unc.edu/Shows/EMS/seasons.htm

Instructional Sequence:

Shadows- In what ways do shadows move? (Best on a sunny day)

As a class, introduce the phenomenon that will be under investigation in this lesson: the relative movements of shadows across different seasons. This lesson will begin with looking at how shadows change within a day, and students will build on that knowledge to develop a model for the causes of changing shadows across seasons. Frame this lesson by asking students if they have noticed their shadows before. Ask students what kinds of things they have noticed about their shadows- on different types of days, at different times of the day, anything they have found interesting. If you have an interesting story to share, this could be a great way to encourage creative student thinking by providing examples- remember, the purpose of this part of the lesson is to create interest for the investigation, and to establish student prior knowledge (e.g., students prior knowledge about the orbit of the Earth causing daylight/nighttime, shadow changes, etc., as expected in 5^th grade). Ask students to share their thinking, following up with student share-outs by asking specific questions related to what the students said. After students have had a chance to discuss their thinking, ask the students to discuss with a partner what they know about shadows and share out with the class. Tell the students they should make notes (using words, diagrams, drawings, concept maps, etc.) to help keep track of their thoughts. Some questions you may provide students with as prompts could include:

• How are shadows made? How do you know this?
• Does a shadow change? Why or why not?

As students are brainstorming, walk around the room and listen for student misconceptions and questions that are arising. As students share their ideas with one another, ask them to come up with at least two questions they have about shadows, how they move, and/or how they change. As a class, have students share their thinking and their questions- record their thinking and questions in a place where everyone can see. You can create a “Know-Want to know-Learned (K-W-L)” chart as a mechanism to help students keep track of their thinking, updating it throughout the course of the lesson. Help students focus on their questions that are about shadows changing, and their reported ideas about why this might be happening. Ask students to brainstorm what they might need to find out or do, to help them answer their questions. As you walk around the room, use questions to probe student thinking. As a class, inform the students that they will have an opportunity to observe and record their shadow at various times of the day- based on their questions and current thinking, ask students (with a partner) to describe when they would want to measure their shadows, any other information they would want to have (e.g., sun position in the sky, time) and to provide a rationale for their choices, tying back to their current understandings and their questions. (If this activity is not possible in class because of weather or time considerations, create an example to prompt discussion or send the students home with the assignment over the weekend. By giving students some decision-making power here, you can generate a nice range of data, and ensure that the data set is large, times are replicated by multiple students, and a wide range of times (early morning and late afternoon/evening, if students take this home) are represented. You can use this as a formative assessment opportunity, to look for student performance across: 1) certain aspects of planning investigations, 2) evidence and reasoning-based thinking, 3) their current content knowledge; all of these should help guide how you approach other parts of this lesson.)

For shadow drawings

• Give each pair:
  • A yardstick to measure the length of shadows in each shadow drawing.
  • A watch or some other method for recording the time.
  • At least 2 different colors of chalk, one for each student (note: you can have students use the same chalk but they should label their shadow with their initials.)
• Ask each student to bring their lab notebooks, to record the time and (using a picture/drawing) the relative position of the sun in the sky, as well as other observations they might make.

Find a flat hard surface outside exposed to the sun for the students (i.e. a sidewalk or play yard). Remind students to NEVER look directly at the sun while doing this activity. Have the students partner up to draw each other’s shadow. Have the students pick a spot to draw their shadow. They must use the same spot and stay in the same orientation for each drawing. If not they will not be able to accurately observe differences.

Direct students to begin tracing by outlining their partner’s shoes or feet; this is especially important to be able to return to the same spot to draw the outline at a later time.

Ask the students to stand up straight when their shadow is being measured, and to mark the head of the shadow for their partners. Then ask students to measure the length of their shadow drawing from the shoes to the head and write the measurement by the top of the head, as well as in their notebook (note: you can have students stand in the exact same spot as their partner and record their shadows- this might help them see different types of patterns, or some patterns more clearly- for example, a taller students shadow might be longer, but follows the same general pattern of change throughout the day. It will also allow them to have at least two sets of data taken at exactly the same place and (approximately) same time). Remind students of what they discussed previously and ask them to draw a diagram of where the sun’s position in the sky is relative to their position when recording the shadow, and to record the time (note: depending on what students described wanting to record earlier, you may decide to simply record this information yourself, and allow students to come to the understanding that they need this information later as they pursue the investigation- this would be a stronger way to develop an understanding of both the DCI and the practices, particularly around planning an investigation- however, this may take quite a bit of additional time and could require another shadow measuring day. One option would be to not have them record this unless they thought to do it ahead of time- if some students record it, they can describe why they did and share their information with classmates as they ask for it; or you can record the information and provide it to students as they ask for it. If you choose to use either of these modifications, make sure you follow through in the subsequent shadow measurements.)

Ask students to notice shadows of other objects in the area, and to record their observations, including patterns that they see. Ask students to discuss patterns (e.g., similarities and differences) that they see (e.g., that all shadows point in the same direction, opposite where the Sun is; shadows have a distorted shape (e.g., really long) relative to the object).

Ask students to predict whether and how their second and subsequent tracings of their shadows might change over time, and to justify their predictions- they can write down their thoughts in the lab notebooks, use drawings, share their ideas verbally with a partner, and/or mark their predictions in a different color chalk on the ground itself.

Have the pairs return to their outline spots at the subsequent times that they chose, stand on the outlined “shoes” and draw another shadow outline and note the time and position of the sun again. Repeat this 3-4 times, according to the students plan formed earlier in the class.

Instruct the students to take the time, sun position, and shadow measurements during their other shadow drawings. Ask students to make predictions again, using the patterns they have observed to justify their thinking (written, diagrammed, oral).

Throughout the rest of the investigations you can have the students repeat the activity at the same times of the day to see if their shadow has changed. If possible you can revisit this activity throughout the year to see what patterns emerge from their changing shadows at different months/seasons. Each time, ask students to use the patterns they have observed and recorded to justify their predictions- by observing how student predictions and justifications change, this can serve as both deep learning opportunity for students as well as a formative assessment opportunity.

After students have had the opportunity to measure their shadows throughout the day, revisit the driving question: why do our shadows move throughout the day? Ask students to:

• revisit the questions they had earlier
• as a pair, choose a question they want to answer (encourage students to choose questions that have to do with why the length or direction of shadows change across the day)
• analyze their collected data to find patterns that address the question
• make a claim in response to the question (note: keep an ear out for multiple claims, and student conversation around those claims if they happen)
• justify the claim with patterns/relationships from their collected data

As students select their questions, ask them to organize their own data (in their pair) such that they can easily observe and share the patterns that they see in the shadows. Depending on student familiarity with tables and graphs, you may want to first go through an example as a class. If so, make sure the students are driving the experience- ask them what they want to know, what parts of the data will help them see that, and how to arrange them. Rather than telling students information about variables and organizing data, use guiding questions to help them consider their decisions. For example:

Questions to help facilitation:

• What do we want to know about? What part of the data we collected shows us this?
• What are some ways we can represent the data so that we can look for patterns?
• A student suggested using a bar graph- how should we plot the data?
• If we represented the data in this way, what types of patterns can be observed? What if I wanted to know about X? Would this help me see that pattern? If not, what would we need to see that pattern?
• What about the observations that we made but didn’t necessarily measure? Are those important? What do we want to know, based on them? How should we represent these observations, to allow us to see patterns?

If you opt to have students create their own graphs/tables/charts without the initial class-wide piece, use these types of questions as you walk around the room, to help push student thinking. Remember, depending on which questions students choose, and what observations they chose to make, different groups may choose very different ways to represent the data, and each group may or may not be able to support their claim- that’s okay! The point here is to give students an opportunity to develop their thinking around 1) making claims that can be supported, 2) organizing data and looking for patterns, 3) using patterns in data to support and justify claims, in the context of daily patterns. Give students an opportunity to follow through on their misconceptions, build their understanding, and then revisit this work again to update their claims, graphs, and justifications as their thinking changes.

After students have had an opportunity to work in their groups, ask students to present their work. Encourage students to think critically about their claims and evidence, and really probe them on what the patterns mean, and what makes them think that. Ask students to come up with ideas for what other information they might need, and describe why that information would be helpful- you can have the class do this together, or have student pairs collaborate to come up with ideas, and share them as appropriate. As students work, push their thinking about patterns and cause-and-effect relationships, and how the information they are missing would help them identify those relationships.

After students have had an opportunity to reflect critically on their process as it related to their questions, you could have them draft an investigation plan that reflects their most recent thinking, the question they want to answer, appropriate variables, and descriptions of why they have changed parts of what they did, or why they have kept some things the same to describe the desired patterns- if time permits, and students are interested, you could even allow them to do the experiment again. Alternatively, you could move onto the next portion of the lesson, using cumulative classroom data, or data that you provide (in instances where it is missing).

Alternative Tools of Engagement:
As an alternate to having the students answer questions to gauge their understanding, use the above questions for a short writing exercise or an annotated drawing explaining the activity and phenomena observed.

Initial ideas revisited:
Take a few minutes to engage the students in a discussion reflecting on what they have learned using the prompt “What are some patterns we observed about shadows? What do you think causes those changes that we observed?” Students should draw on their observations or their newly developed understanding of phenomena gained during the activity.

Investigation 2: What causes shadows? Developing a model to demonstrate the relationships underlying shadow changes within a day

Materials per group

• Heat lamp/lamp without shade (a flash light could also be used, but a stationary, light source that can give off light in all directions would be a better representation)
• Objects (e.g., ball, pencil)
• Chart paper
• Markers

Remind students of the question at hand: what causes changes in shadows within a day? Ask students to revisit their thinking and findings from the previous investigation, and tell them that they will create a model to answer this question (note: depending on the questions students chose in the previous investigation, this may flow very nicely, or may require a transition, to build coherently on student thinking).

In groups, ask students to consider this question, and to decide what will be necessary to represent in their model (e.g., the sun, the Earth, an object on earth, etc.), based on what they have learned so far. Allow the groups to know what materials are available to them- they may find it helpful to use the light source and objects; alternatively, they may want to draw their thinking, or even do something kinesthetic- or a combination of them all! Allow students the flexibility to develop the model the way they want to, and encourage them to be excited with the flexibility and creativity! (note: students should have already covered light-object interactions producing shadows n 4^th and 5^th grade, such that they can simply utilize that understanding here; however, if that experience was insufficient, or if students require additional experiences with shadow creation and manipulation, allow them time to recreate the shadow patterns they observed with the lamp and objects before asking them to create the earth-sun-shadow model.)

Remind students what their model should be explaining- why shadows change throughout the day. After students have developed their model, ask them to consider their model, and what types of information they could use the model to generate. Based on this thinking, ask student groups to generate 3 questions in their group that they could use to probe other students models- encourage them to think of “what if” questions- for example, “based on your model, what would you expect the pattern of shadow changes to look like in the data if the day last 5 hours instead of 24 hours?” or “what would you expect if the Earth’s axis of rotation changed?”- tell them to make sure they could answer it based on their own model, and to think about what kind of feedback not being able to answer the question might help them provide their classmates- or themselves! You can have them record their thinking if you like, or just walk around and listen to their conversations (note: this part of the exercise is intended to give students an opportunity to really think about modeling, and what they should be able to do with a model- it may also introduce a creative element, and set students up for thinking through limitations of a given model. This also gives the students an opportunity to thoroughly engage in crosscutting concepts- you can even encourage students to use their knowledge of cause-and-effect to both create and respond to questions). As you walk around, listen for student thinking- they should be using:

• Their understanding of the idea that the Earth orbits around the sun (prior)
• Apparent movement of the sun across the sky (prior; observations from investigation 1)
• Light-object interactions that lead to shadows, and how changes in the angle/position of the light relative to the object and relevant surfaces
• Earth’s rotation on its axis
• Patterns observed in the data and from their previous experiences
• Cause and effect relationships, as implied by multiple lines of evidence

After students have created their models and noted their questions, ask students to share their thinking- you can have students demonstrate their models for the class, post drawings, etc. Make sure students have the opportunity to both share their models as well as ask other students questions about the models. Depending on where students are in their progression for evaluating evidence, reasoning, and models, you may want to give students specific guidance about their questions and keeping the feedback/responses constructive, respectful, and grounded in their observations, data, and models.

Facilitate a rich discussion about the models with the students, ensuring that they have a shared understanding of how the earth’s rotation- and the subsequent differences in exposure of a given point to the sun- causes shadows to exhibit daily patterns. Then pose the following question to students: “Given what you know about shadows, their daily patterns, and their causes, do you think your shadow will look the same in 6 months, at a given time in the day?” Ask students to consider the evidence they have gathered so far, including the thinking represented in their models, and then to think of at least two claims thy could make about their answer to this question. Then ask them, in their groups, to evaluate the evidence and provide scientific and logical reasoning for which claim is best supported by the evidence. (note: depending on student experience, you may be able to simply ask them to construct an argument; alternatively, they may require additional support for argumentation, such as support around evaluation and critique of the evidence, and reasoning. You could also make this practice piece more rigorous by emphasizing the evaluation of the evidence for sources and sufficiency.)

Investigation 3: Our tilted Earth model: Using patterns in data to create a model of how shadows change across different seasons

Materials per group:

• Models from Investigation 2
• Heat lamp/ Lamp w/o shade

Note: students can use the same materials the used in the previous investigation to refine their model in this investigation. Make sure the students mark the Earth’s axis!

Instructional Sequence:
Use the argument at the end of the last investigation to launch into thinking about daily vs. seasonal changes. Have the students revisit their arguments, models, and other sources of evidence to describe what they think- you can have them share this, or share out what you have gathered from their arguments. Make sure that the idea that shadows don’t change across seasons is represented- students will develop a model to refute this through the subsequent investigation. However, students may also cite experiences with shorter days in the winter, longer days in the summer, etc. Allow students to share all their thinking, and remember to link back to seasons later.

Tell students that you have data for your own shadow from a different season from last year, which they will analyze to determine whether the shadows approximately follow the same patterns. (note: you will have to create this based on when you teach this lesson, such that the created data are from a very different season- just make sure they follow the appropriate patterns, and that students will be able to sufficiently see the differences in shadows.)

Ask students to analyze this data to allow them to determine whether shadows change with seasons (note: depending on student experience with analyzing data, they may need support in what analyzing data looks like; appropriate graphs and charts, comparing similarities and differences, etc.). They can do this in the same groups they have been working with, and ask them to produce something to show their thinking (e.g., a graph or chart). As students are working, walk around and facilitate conversations- what differences do they see? Are there patterns that are similar? Why are they not exactly the same? Are there limitations to your conclusions, because of the analysis options/data available?

As students determine that shadows are, in fact, different in a different season, ask students what the causes might be. Make a list of student ideas. Then ask students to use their ideas, as well as their knowledge of the Earth-sun system, to hypothesize ways that the shadows may change with seasons. Encourage students to return to and use their models, or to create new models to organize their thinking- as you walk around, ask questions to encourage students to explore their ideas. For example, ask students what they know about how the Earth rotates and revolves around the sun- what happens if the axis is turned 90 degrees? Encourage students to play around with the orientation of the axis as they think through this.

Give the students time to create/modify their models with the materials provided. Then ask students, based on their investigation, to describe their hypothesis for why shadows are different across the year. Based on this hypothesis, what are some specific expectations they may have? Tie this to shadows as well as day length, which can provide a nice lead into following lessons about seasons and Earth-sun system interactions. Give the students an opportunity to see each other’s designs and give constructive feedback. Encourage the students to be helpful in their feedback.

Once the students have made some observations about shadow changes at different points in the year, ask students to think about what this means in terms of the direct and indirect sunlight on different parts of the Earth at different points in the year (Earth’s revolution around the sun). This will set students up for future lessons dealing with solar energy.

Discussion Questions:

• What do you observe?
• How is the shadow created?/Where does the light come from?
• What is happening to cause the differences in the shadows?
• Do you think you would see your shadow at different days of the year at the same exact time? What do we know about the sun’s movement in our sky throughout the year? How is this related to the movement of the Earth?

Questions to guide students feedback:
What were some functional parts of the model? What are some things that worked well? Was there something missing on the model or data that was unable to be collected as a direct result of the model being inaccurate? What are some suggestions you would give that group?

Alternative Tools of Engagement: If students are struggling to connect the phenomena observed with the sun Earth interaction take time between investigations to have smaller group discussions to gauge their understanding and help clarify any misconceptions students may still have.

If students are still struggling you can kinesthetically model the sun-Earth interactions by having the student “sun” use a flashlight to shine direct sunlight on another student representing Earth and have them feel if there is a temperature change. Students should also note the area the flashlight’s light covers. Direct the “sun” students to tilt the flashlight a bit to create a larger spread of light on the “Earth” student. This slide show also illustrates the tilt and indirect and direct sunlight the Earth receives at different seasons http://www.slideshare.net/kmacdevitt/seasons-10676010

Investigation 4: Shadows Presentation

Instructional Sequence:
Now that we know more about the reason why shadows change across seasons on Earth, tell students that many people are confused about why the tilt of the Earth was important for determining the cause of shadow patterns across a whole year, but not within a day. Based on their investigations, they are going to help people understand this issue of scale. Ask each group to create an analogous scale example to help illustrate their thinking to their peers and those who may be confused- they can be as creative as they like here, both in terms of the analogy as well as in their presentation format, as long as they can justify their analogy’s relevance to the question. Their presentations should include the evidence gathered from the shadow drawings, data they analyzed and interpreted throughout this lesson, the graphs they made, the internet sources and the experiments they did with the models their groups created. If needed the students can do further research and the groups can present their findings to the class, if appropriate- alternatively, they can choose a different way to communicate their ideas (e.g., video presentations, story board, visual or audio creative presentations).

As students develop their presentations, provide opportunities for check in meetings. This will help you address any challenges the students are facing and encourage that students are coming up with different, creative analogous scale examples so that there are a variety of presentations.

Assessment: Our Tilted Earth Rubric
Once you have introduced the presentation give the students a copy of the rubric and engage them in a discussion about the rubric so they are aware of the criteria for their presentations. Give the students an opportunity to add any elements to the rubric they feel is important for assessing their presentations. Use the modified rubric with the students’ feedback to give the groups feedback on their presentations.

Alternative Tools of Engagement:
If a student cannot present their findings orally have other mediums on hand for them to present like captioned pictures/powerpoints, video essays etc.

For higher-level students encourage them to research and create models about shadows on other planets. Things to consider are the composition of the atmosphere or lack of atmosphere of other planets, the distance from the sun from the planet and the sun/planet interaction. This added layer can be incorporated into the presentations.

Feedback- Two Stars And A Wish
Inform the class before the presentations start that they will be giving feedback to the teams giving their presentation using a method called two stars and a wish. Each team will write down two positive things they saw or learned during the presentation and one thing they wish the presenting team mentioned. All feedback should be constructive and helpful.

Resources:
Living Maya Time: Observing and Tracking Shadows. http://maya.nmai.si.edu/sites/default/files/resources/lesson-plans/Observing%20and%20Tracking%20Shadows.pdf