Using Personal Observations to Understand Changing Sun Patterns from an Earth Perspective

Transcription

1 Sunrise, Sunset Using Personal Observations to Understand Changing Sun Patterns from an Earth Perspective BY PEGGY MCNEAL, TODD ELLIS, AND DAVID RUDGE 78

2 Misconceptions about Earth Sun relationships abound (Salierno, Edelson, and Sherin 2005). Many students think that the seasons are caused by Earth s changing distance to the Sun and those who recognize Earth s tilt as the cause often have difficulty explaining this in terms of Sun angle and length of day. Ask a student the location of sunrise and sunset and they are likely to tell you east and west. In reality, the Sun rises due east and sets due west only two days a year. Many students believe that the Sun is directly overhead at noon, but outside of the tropics, a simple observation will prove this thinking incorrect. Recognizing that misconceptions are perniciously difficult to overcome, the lessons presented here attempt to create instances of dissatisfaction with current thought (see Posner et al. 1982) and encourage middle school students to connect with the Sun s changing position from an Earth perspective. By making personal, Earth-bound observations, students can connect their new knowledge in a relevant and exciting way. Through fostering student observations and critical thinking, we hope to provide students with opportunities to draw conclusions from evidence that lead to deeper understanding. Lesson goals The goals of these lessons are to help middle school students recognize Sun patterns from an Earth perspective that will advance their understanding of Earth s place in the solar system. Through the use of models and personal observations, these lessons are designed to help students: observe that the length of the path of the Sun across the sky, and hence the length of day, changes in a predictable pattern over the course of a year; notice that the elevation angle of the Sun in the sky, and hence the Sun angle (the angle between a horizontal plane at the Earth s surface and the incoming sunlight), changes in a predictable pattern over the course of a year; and recognize that varying Sun angle and length of day change the intensity and length of exposure to the Sun, thus affecting temperature and causing seasonal change. Although the Sun rises and sets every day, many students are oblivious to the Sun s change in position. Thus, an additional goal is to engage students with natural phenomena in an authentic and personal way that drives discovery and accommodation of new knowledge. Engage: Assessing prior knowledge and connecting students with Sun patterns (Day 1) To assess student knowledge, identify misconceptions, and stimulate thinking, students provide individual written responses to the preassessment questions in Figure 1. This important first step identifies students misconceptions and gaps in knowledge, which serves to focus instruction and ongoing, informal formative assessment. In our experience, we find that many of our students hold common misconceptions, including thinking CONTENT AREA Earth science GRADE LEVEL 6 8 BIG IDEA/UNIT Earth s place in the solar system ESSENTIAL PRE-EXISTING KNOWLEDGE Students should be able to identify cardinal directions, know how angles are measured, and have conceptual understanding of Earth s motion in the solar system (e.g., rotation and revolution). TIME REQUIRED The lessons require three class periods. Extension activities (photo documentation and measurements of Sun angle) occur over several months. COST Costs are minimal and include materials for making clinometers (straws, cardstock, steel nuts). March

3 FIGURE 1: Preassessment questions monument in Peru that served as an astronomical observatory. Built in the fourth century BCE and consisting of 13 towers, the monument provided citizens with the ability to determine an accurate date by observing the sunrise or sunset through the correct tower (Ghezzi and Ruggles 2007). Explore and Explain: Building student understanding of Sun patterns (Day 2) that the Sun rises due east and sets due west, that it remains at the same angle throughout the year, and that the Earth is closer to the Sun in the summer. After addressing these questions, the lesson continues with students viewing projected photos of sunrises or sunsets, such as those in Figure 2. (Until teachers have collected their own examples of sunrise and sunset photos, Figure 2 can be used for instruction.) By projecting the images individually and sequentially while pointing out reference points, cardinal directions, and dates, the teacher can build anticipation and stimulate questions such as, Why isn t the Sun rising in the same place every day? Next, working in small groups (we use groups of four) and referring to the photos, students discuss their observations of the Sun s position, identify patterns, and report conclusions. (We use small whiteboards for displaying group conclusions.) In our experience with this activity, we find that most students easily grasp the point of the exercise and quickly move to discussion. Many students recognize that the specific direction evident in the photo (e.g., the Sun was setting to the southwest, not west) challenges what they said in response to the preassessment questions. As intended, this provokes interesting discussion; however, discovering the reasons behind this phenomenon is saved for a later lesson. As a conclusion to this lesson, students view a fascinating, short video about Chankillo, an ancient In this lesson, students model Earth Sun relationships using simulators hosted on the Astronomy Education at the University of Nebraska Lincoln website (see Resources). A student worksheet and key for use with this lesson can be accessed in this article s online supplemental materials. With the first simulator, Motions of the Sun, students model the path of the Sun across the sky throughout the course of a year (Figure 3). Although instructions for students are included on the worksheet, it is beneficial for students to watch the teacher demonstrate the features of the simulator, including how to set the simulator to students latitude, set the simulator to the equinoxes and solstices, and how to model sunrises, sunsets, and the path of the Sun across the sky. By controlling the animation speed and observing the clock, students can time the length of day. As students work through the worksheet in small groups (we use groups of four, with each student individually completing a worksheet), group discussion is stimulated with the following worksheet questions: In what direction is the sunrise/sunset located on the following days: March 21, June 21, September 21, and December 21? How long (in hours) is daylight on each of the above dates? What is causing the difference in day lengths? What effect will length of day have on temperature? 80

4 SUNRISE, SUNSET FIGURE 2: Sunrise photo series By checking in with groups, the teacher can guide conversations, answer questions, and help students overcome misconceptions. In our experience with this lesson, students usually answer three of the four questions quickly. However, they spend much time debating the remaining question. Prompting students with questions about the Sun s apparent motion and speed across the sky, rotational rate of the Earth, and shape of the Earth s orbit helps students distinguish between scientifically inaccurate answers and potential contenders. However, because of the spatial challenges inherent in these concepts, some students continue to grapple with them. Figure 4 provides some prompts for helping struggling students with sense-making. The second simulator, Seasons and Ecliptic Simulator, allows students to model Sun angle (Figure 5). Again, although instructions are included on the student worksheet, a teacher demonstration is important. Students can drag the arrow bar along the list of months to compare Sun angle at the equinoxes and solstices. Students can toggle between sunbeam spread and sunlight angle to experiment with each. Group discussion is stimulated as students work together through the questions on the worksheet: What is the highest Sun angle (Sun s altitude) on the following days: March 21, June 21, September 21, and December 21? Describe or draw the sunbeam spread for each of the above dates. What effect will varying Sun angle and sunbeam spread have on temperature? Why? In our experience, students find the concepts relating to the second model much easier to understand. Students who may benefit from a kinesthetic experience can model this phenomenon with a flashlight. March

5 FIGURE 3: Screenshot of the Motions of the Sun simulator hosted on the Astronomy Education at the University of Nebraska Lincoln website A quick check for understanding via individual responses on exit tickets serves to evaluate student comprehension levels. The next activity is designed to promote an even deeper understanding by having students witness what their models portrayed. FIGURE 4: Prompts for student discussion Could it be because the Earth sometimes spins faster? When the Sun moves across the sky, maybe sometimes it goes fast and sometimes it goes slow. Could it be because the Earth s orbit isn t a perfect circle? Does it have something to do with the Earth s tilt? Speed = distance time. So if the Sun s speed doesn t change, but the amount of time changes, what else must change? Is it because sometimes the Earth is closer to the Sun? Extend: Developing observation skills and collecting evidence (Day 3) Based on the previous lessons check for understanding, the next lesson begins with a differentiated review and extension activities. Students who have demonstrated mastery of the concepts progress to working with the more challenging Rising and Setting Azimuths A and B Interactives (see Resources). These interactives include a grade me function, allowing groups of students to work independently and freeing the teacher to continue working with students needing extra instruction. Through continued modeling of Earth Sun relationships, all students progress toward understanding the mechanisms underlying observed Sun patterns. In keeping with promoting an understanding of Sun patterns from an Earth perspective, however, this final lesson asks students to make measurements of Sun angle with a clinometer and photograph or sketch of the Sun at sunrise or sunset (see Safety Precautions, Figure 6). These observations are used to validate the concepts that students developed from the models. To measure Sun angle at solar noon (the time of the Sun s highest point in the sky for any given day), students first make clinometers using a template and materials such as cardstock, string, and a steel nut. Easy instructions for building simple clinometers and directions for measuring Sun angle are available on the Global Student Laboratory website (see Resources). Next, students determine the time of solar noon for their location and specific observation dates using the NOAA solar calculator (see Resources). Subsequently, students measure 82

6 SUNRISE, SUNSET FIGURE 5: Education at the University of Nebraska Lincoln Web Site FIGURE 6: Safety precautions emphasizes the importance of taking photos from the same location. Students can mark where they stand by outlining their footprints with duct tape or paint. A point of reference in the photo is necessary, such as a tree, telephone pole, or billboard. Additionally, students must understand that the Sun needs to be in the picture and not below the horizon in order to ascertain its position. Students without access to cameras can sketch the position of the Sun on the horizon, along with an object they use for reference. We have our students complete a trial Sun angle measurement (using their homemade clinometers) and photo (or sketch), and we provide feedback. This catches early errors and works out any bugs before students progress deeper into the project. Evaluate: Using observational evidence to validate models and demonstrate understanding (final task) and record Sun angle once a month for the duration of the activity using their homemade clinometers. To document the position of the Sun on the horizon at sunrise or sunset, students take monthly photos. This is the most exciting part for our students. They enjoy creating and sharing their beautiful photos and get excited about witnessing what they learned in class the Sun really does follow a predictable pattern! Students may choose to photograph or sketch either sunrises or sunsets; however, they need to be consistent once they make their choice. It is also important that the teacher As a motivating final project and method for assessing student learning, students are asked to compile their Sun angle measurements and photos (or sketches), along with a short essay. (See Figure 7 for an example of student work.) We ask our students to submit this electronically in a Word document or PowerPoint slide (it can also be printed or hand composed). A rubric for scoring this assessment can be accessed online (see Online Supplemental Materials). The essay addresses the following prompt: Describe how Sun angle, position of the Sun on the horizon at sunrise or sunset, and length of day March

7 change over the course of the year. Relate your description to your pictures, compass directions, and clinometer readings. Include the following terms: sunrise/sunset, path of the Sun, length of day, Sun angle, and temperature. FIGURE 7: Final student project Conclusion There is no doubt that mentally translating from a space perspective to an Earth perspective is a difficult yet necessary part of fully understanding Earth s place in the solar system, Earth Sun relationships, and resulting phenomena. Using personal observations to scaffold these spatially difficult concepts makes them more accessible; nevertheless, some students will continue to grapple with the two perspectives and need time to mentally consolidate them. By engaging with the natural world and documenting their observations, students connect with science in an authentic way that promotes scientific thinking. It is our hope that these activities will kindle interest and encourage students to purposefully seek connections between their personal experiences and the science classroom. REFERENCES Ghezzi, I., and C. Ruggles Chankillo: A 2,300-year-old solar observatory in coastal Peru. Science 315 (5816): NGSS Lead States Next Generation Science Standards: For states, by states. Washington, DC: National Academies Press. Posner, G., K. Strike, P. Hewson and W. Gertzog Accommodation of a scientific conception: Toward a theory of conceptual change. Science Education 66 (2): Salierno, C., D. Edelson, and B. Sherin The development of student conceptions of the Earth Sun relationship in an inquiry-based curriculum. Journal of Geoscience Education 53 (4): RESOURCES Instructions for clinometers Mind-blowing Ancient Solar Calendar video clip ly/2hszmcn Motions of the Sun simulator NOAA solar calculator Rising and setting azimuths A and B interactives ly/2gvumx6 Seasons and Ecliptic simulator ONLINE SUPPLEMENTAL MATERIALS Rubric Sunrise Sunset worksheet and key Peggy McNeal (peggy.m.mcneal@wmich.edu) is a doctoral candidate at the Mallinson Institute for Science Education at Western Michigan University and a former middle school science teacher at Los Coches Creek Middle School in El Cajon, California. Todd Ellis is an assistant professor, holding joint appointments in the Department of Geography and the Mallinson Institute of Science Education at Western Michigan University. David Rudge is an associate professor, holding joint appointments in the Department of Biological Sciences and the Mallinson Institute of Science Education at Western Michigan University in Kalamazoo, Michigan. 84

8 SUNRISE, SUNSET Connecting to the Next Generation Science Standards (NGSS Lead States 2013) The chart below makes one set of connections between the instruction outlined in this article and the NGSS. Other valid connections are likely; however, space restrictions prevent us from listing all possibilities. The materials, lessons, and activities outlined in the article are just one step toward reaching the performance expectations listed below. Standards MS-ESS1: Earth s Place in the Universe Performance Expectations MS-ESS1-1. Develop and use a model of the Earth-Sun-Moon system to describe the cyclic patterns of lunar phases, eclipses of the Sun and Moon, and seasons. DIMENSIONS CLASSROOM CONNECTIONS Science and Engineering Practice Developing and Using Models Students work with models to begin to build an understanding of the mechanisms underlying observed Sun patterns. Disciplinary Core Ideas ESS1.A: The Universe and Its Stars Patterns of the apparent motion of the Sun, the Moon, and stars in the sky can be observed, described, predicted, and explained with models. Students answer questions such as: In what direction is the sunrise/sunset located on the following days: March 21, June 21, September 21, and December 21? How long (in hours) is daylight on each of the above dates? What is the Sun angle (Sun s altitude) on the following days: March 21, June 21, September 21, and December 21? Students describe or draw the sunbeam spread for each of the above dates. Crosscutting Concepts Patterns Students discuss observations of the Sun s position to describe the predictable pattern the sun takes at different times of the year Connections to the Common Core State Standards (NGAC and CCSSO 2010) ELA CCSS.ELA-LITERACY.RST.6-8.3: Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks. Mathematics CCSS.MATH.CONTENT.7.G.B.5: Use facts about supplementary, complementary, vertical, and adjacent angles in a multi-step problem to write and solve simple equations for an unknown angle in a figure. March