Scientists often deal with

Solar System in the Hallway by Malonne Davies, Linda Landis, and Arthur Landis Scientists often deal with extreme numbers, both large and small. The Earth, 12,756,000 m in diameter, has a mass of 5,973, 700,000,000,000,000,000,000 kg and is 149,579,890 km from the Sun. Most students, even most adults, are not able to grasp the size of our solar system. Scale models are one means of bringing extreme sizes into better focus, cutting them down to relative values that we can better comprehend. After studying phenomena related to the positions and motions of the Earth, Sun, and Moon, many students are familiar with the positional ordering of the planets, but their knowledge of the distances involved is vague. The Solar System in the Hallway activity consists of a scale model of the interplanet distances set up in a hallway for students to explore. During class discussion of the pre-activity questions (see Activity Worksheet), we find that students believe the planets are fairly uniformly spaced and that the inter-planet distances are not very large. When asked how much of the hallway will be needed for the entire solar system if Earth is 10 tiles from the Sun, students consistently estimate the distance needed to be half or less of its actual value. A series of questions (see Procedure in the Activity Worksheet) guides students exploration of the model. One aspect of the exploration is timing their heel-to-toe travel within the solar system. Students are amazed at how long it takes to travel from the Sun to Neptune their appreciation for the distances involved seems to change at this point. During the Sun-to-Neptune trip, students discover that once they pass Mars, it seems FIGURE 1 Tile counts for Solar System in the Hallway activity Object Number of tiles Distance from Sun (AU) Sun 0.0 0.0 Mercury 3.9 0.39 Venus 7.9 0.79 Earth 10.0 1.00 Mars 15.2 1.52 Asteroids 26.7 2.67 (optional) Jupiter 52.0 5.20 Saturn 95.4 9.54 Uranus 192 19.2 Neptune 301 30.1 56 SCIENCE SCOPE

Photos courtesy of the authors FIGURE 2 FIGURE 3 Students collect data during activity Using the heel-to-toe method, a student travels from Earth toward Venus to take forever to get to the next planet, Jupiter. We adapted this activity from Project Earth Science: Astronomy (Smith 1995). Our activity differs from Smith s in that we provide students with a scale model of inter-planet distances while Smith has students calculate the scaled distances, then lay out the model. We feel that having the students experience or explore the model solar system helps to internalize the relative magnitudes involved, whereas the calculate-the-scaledistance approach helps them appreciate the mathematics involved. The Activity Worksheet is designed to focus students attention on the scope of the solar system and related science. The only resources needed for this activity are a long, tiled hallway (at least 310 tiles); signs for the Sun and each planet; rulers; and stopwatches (or similar timers). The activity can also be conducted outdoors, weather permitting, on a sidewalk, playground, or sports field. In this case, the tile counts can simply be converted to feet or any other convenient measuring unit. Figure 1 shows the distance from the Sun in number of tiles and in astronomical units (the average distance from the Sun to Earth, approximately 150 million kilometers). The AU values used in Figure 1 are the standard values found in textbooks and on the internet. The tile counts are the AU values multiplied by 10. Note that in the post-activity questions, students determine the distance represented by each tile in the model; that is, they calculate the scale used for the model. Prior to the class session, the teacher places signs at the correct tile position for each planet in the April/May 2009 57

hallway. Figure 1 provides the tile counts for the teacher. However, students should not have access to this information until they are working on item 4 of the post-activity questions (see Activity Worksheet) because they are asked to collect this as data while exploring the model. The signs can be just the name of the planet (in large font on a sheet of paper) or they can have a picture and the planet s name. Ideally, the signs would be supported on a post for visibility. However, the activity will work just as well with the signs placed on the floor, as long as they are anchored in place for the duration of the activity. Each student gathers and records data (see Figure 2). We facilitate the data gathering by having only six to eight students using the hallway solar system at any one time. Students are instructed to collect their data quietly and not to disturb other classes. The small number of students using the solar system model at any one time improves the individual data collection and students awareness of the relative distances involved. A larger group usually negates much of the individual s awareness because views are blocked and students tend to interact more with each other rather than with the model. While students are exploring the model, the teacher will need the assistance of a second adult to supervise either the classroom or the group in the hallway. A paraprofessional or a parent could fill this role. While exploring the hallway model, students make general observations of the solar system, and then look for the smallest and largest inter-planet distances. They then measure the apparent diameter of the Sun as seen from Earth and again as seen from Neptune. The final data-collection tasks involve counting tiles between specific planets and timing their heel-to-toe trip from the Sun to Neptune. Students are instructed that the heel-to-toe walk must be done by placing the heel of each foot, in turn, directly in front of and in contact with the toe of the other foot. The Procedure section of the Activity Worksheet provides more detailed instructions concerning the data to be collected. Most students require about 15 minutes to complete the data collection. Figure 3 shows a student making the heel-to-toe trip from Earth toward Venus. Although the time required to travel heel to toe is not scaled to real travel times, it does serve to reinforce students perception of the spatial dimensions of the solar system. Figure 4 shows the Solar System in the Hallway as a student measures the apparent size of the Sun from Earth. This task is included to reinforce the concept that distance affects perception. The Activity Worksheet: Solar System in the Hallway Purposes To better grasp the order of the planets from the Sun and the relative distances between objects in our solar system To review and use math skills related to scale calculations involving time and distance (average velocity or speed) Pre-activity questions 1. can you state the order of the planets from nearest to the Sun to farthest away? 2. Do you think the inter-planet distances (distances between neighboring planets) are uniform? 3. If not, is there a pattern to the intervals or are the differences random? 4. Suppose we say the Sun is at one end of the hall and we scale the solar system so the Earth is 10 tiles from the Sun. Do you think all of the solar system will fit in the hallway? If so, where will the farthest planet from the Sun be located? Materials Tiled hallway or floor with distance of about 310 tiles Signs for the Sun and each planet (the asteroid belt may be included if desired) Supports for the signs (optional) Rulers (30 cm) Timer for each student in the hallway Procedure 11. The Solar System in the Hallway has a sign for the Sun and each planet. Each planet is in its correct position and its distance from the Sun is scaled based on the floor tiles. Determine and record the following information in your notebook. 12. record some general observations about the Solar representation of the Sun does not need to be of any particular size (no scale-based calculations depend on this), although it should be big enough to be easily seen from Neptune. The greater the distance one is from the Sun, the smaller the Sun appears (apparent size) to be. Using the ruler and recording a measurement is intended only to help draw students attention to how far they have traveled to get to Neptune. A simple way to measure the apparent diameter of the Sun is for the student to hold a ruler at arm s length and record the apparent diameter (diameter of the 58 SCIENCE SCOPE

System in the Hallway, including the order of the planets from nearest to the Sun to farthest away. 13. By sight, what is the closest object-to-object distance? Record the names of the objects and your estimate of the distance in number of tiles. 14. By sight, what is the greatest distance between two adjacent objects? Record the names of the planets (or objects) and the distance between them (in number of tiles). 15. Record the distance (in number of tiles) from the Sun to Mercury. 16. How far (in tiles) is it from the Sun to Earth? 17. When you are at Earth, record how big the Sun appears using your ruler. 18, how far (in tiles) is it from Earth to Jupiter? 19. How long does it take to get from the Sun to Neptune using the heel-to-toe method? 10. how far is Uranus from Neptune (in tiles)? 11. When you are at Neptune, record how big the Sun appears. The size of the Sun, or its sign, can be measured at each position (Earth, Jupiter, and Neptune) by holding a ruler at arm s length to determine the apparent diameter of the Sun picture or the length of the sign. Post-activity questions 1. how well did you predict (in the pre-activity questions) the overall size of the solar system? 2. Are the inter-planet distances uniform? 3. Is there a pattern to the inter-planet intervals? 4. Look at the table of planet distances (in tiles) provided. Was your estimate of which objects were closest together correct? Was your choice of the greatest object-toobject interval correct? 5. If the distance from Sun to Neptune is 301 tiles, what was your average velocity (speed) during the heel-to-toe walk? 6. Based on your heel-to-toe speed, how long would it take you to go from Earth to Jupiter? 7. the average distance from Sun to Earth is 149,597,890 km. What is the scale used for the Solar System in the Hallway? In other words, what distance does each tile represent? 8. Based on your data and calculations, what is the actual distance (in km) from the Sun to Neptune? Possible extensions 1. Given the distance data for Ceres, Pluto, and Eris, where would the three dwarf planets be on our scale? Would all of them fit in our hallway? [Ceres is 415 million km from the Sun (The StarChild Team, Ceres)]. Pluto is 5.87 billion km from the Sun (Spinrad 2004). Eris is about 10 billion km from the Sun (The StarChild Team, Eris). 2. Students may wish to use the internet to gather information that would allow them to calculate how long it would take for a spaceship from Earth to reach Mars (the first step people consider with respect to exploring the solar system). Time to reach more distant planets can also be calculated, if desired. 3. What has to be considered in planning for humans to travel to and to explore on Mars? Think about both the trip to Mars, exploration phase, and the return trip to Earth. 4. research NASA s recently launched Pluto probe (New Horizons Probe). When did it leave Earth, when will it arrive in Pluto s vicinity, and what kind of information is it designed to gather? 5. Students could participate in a crosscurricular activity relating science and history by researching and constructing a time line of the discovery and discoverers of each planet. This might be extended by including the new classification of dwarf planets. Sun s picture as shown on the ruler). Figure 4 shows a student making a measurement of the apparent size of the Sun. Once they return to the classroom, students work in table groups (three or four students) to discuss and complete the post-activity questions (see Activity Worksheet). The teacher should circulate among the table groups as they work, assisting and answering questions as needed. The set of activities concludes with a general class discussion of the solar system using the postactivity questions as the starting point (see Activity Worksheet). Many students are amazed at how far down the hallway the scaled solar system stretched. Even more remarkable to them is the time required for a heel-to-toe trip from the Sun to Neptune. Most students had not realized that the inter-planet spacing is not uniform, nor that the inner planets are clustered close together while the outer planets are much farther apart. Their appreciation for the relative distances and the arrangement of the solar system has been greatly increased. In discussing the view from Earth versus Neptune, students often express April/May 2009 59

surprise that the Sun appears as only a small dot from Neptune FIGURE 4 compared to its appearance from Earth. This helps them grasp that the appearance of other bodies in the solar system differs based on one s location within the solar system. The post-activity questions and ensuing discussion serve to assess students grasp of the solar system distance propor tions. For our students, the final performance assessment includes problems using time, distance, and speed as well as a data set to be scaled. For example, students are given a table of the diameters (in km) of planets, dwarf planets, and natural satellites (moons) in alphabetical order. The questions include which is the largest satellite (requiring them to distinguish among planets, dwarf planets, and satellites) or how many satellites are larger than dwarf planet Pluto. As an assessment of their understanding of scaling, students are asked what the scaled diameter of the largest satellite would be if Charon s diameter were scaled to 1.0 cm. Data from the solar system activity is also incorporated in assessment items related to motion, specifically, average speed. The assessment questions are similar to some of the post-activity questions. Given a heel-to-toe walking time from the Sun to Neptune and the number of tiles, students must calculate the walker s average speed (in tiles per minute or second). Additionally, they use the average speed to determine how many tiles the walker would be from the Sun after a specified length of time, or how long it would take to walk between two planets given the number of tiles from the Sun for each of the planets. The majority of students now successfully answer these questions. Another question asked students to explain how their ideas of the solar system have changed during the course of this unit. Most of these answers include how much empty space there is in the solar system; how long it takes to go from place to place; and how the distances never made an impression before. We consider these to be evidence of the successful use of the model in influencing student perceptions of the solar system. Using a ruler to estimate the apparent size of the Sun as viewed from Earth Reference Smith, P.S. 1995. Project Earth science: Astronomy. Arlington, VA: National Science Teachers Association. Resources NASA. Earth lithograph www.nasa.gov/pdf/62209main_ Earth.Lithograph.pdf World Book at NASA: Pluto www.nasa.gov/worldbook/ pluto_worldbook.html The StarChild Team. Ceres: A dwarf planet http:// starchild.gsfc.nasa.gov/docs/starchild/solar_ system_level2/ceres.html The StarChild Team. Eris: A dwarf planet http:// starchild.gsfc.nasa.gov/docs/starchild/solar_ system_level2/eris.html Malonne Davies (mdavies@emporia.edu) is an assistant professor and Arthur Landis is an associate professor in the Departments of Physical Sciences, and Linda Landis is the director of the Science and Mathematics Education Center, all at Emporia State University in Emporia, Kansas 60 SCIENCE SCOPE