Teacher s Guide Getting Started Diane R. Murray Manhattanville College Purpose In this two-day lesson, students will create several scale models of the Solar System using everyday items. Open with discussing the size of the universe and aim to steer the conversation towards the size of the astronomical bodies. Pose questions that make students think about how large one astronomical body is compared to another. How can they create a model that considers the scale of the bodies? Prerequisites An elementary understanding of the Solar System is especially helpful. Students need to be able to use conversions and rates. Materials The table below lists diameters and true mean distance of the planets from the Sun. (source: http://solarsystem.nasa.gov/planets/index.cfm). Astronomical Body Diameter (miles) True Mean Distance from the Sun (millions of miles) Sun 864,337 - Mercury 3,032 36.0 Venus 7,521 67.2 Earth 7,918 93.0 Moon 2,159 N/A Mars 4,212 141.6 Jupiter 86,881 483.6 Saturn 72,367 886.5 Uranus 31,518 1,783.7 Neptune 30,599 2,795.2 Required: Some of the everyday items listed in the table on the second student page and tools to measure these objects. Suggested: Access to the internet or other reference source for finding diameters and mean distances, modeling clay is useful for creating spheres with small diameters. Optional: Spreadsheet software such as Excel, logarithmic graphing paper. Worksheet 1 Guide The first three pages of the lesson constitute the first day s work and focus on gathering measurements and the first attempt at devising a model. Worksheet 2 Guide The fourth and fifth pages of the lesson consitiute the second day s work. Students try two more scales then extend the lesson to mean distance from the Sun. CCSSM Addressed N-Q.1, 2, and 3: Reason quantitatively and use units to solve problems. F-LE.1: Distinguish situations that can be modeled with linear functions. 11
Student Name: Date: Hayden Planetarium, part of the Rose Center for Earth and Space of the American Museum of Natural History in New York City, was redesigned in 2000 to include the Scales of the Solar System exhibit, which shows the vast array of sizes of the planets and the Sun. The exhibit demonstrates the massive size of the Solar System by modeling the astronomical bodies as spheres with the Sun being the extremely large sphere partially visible in the top left corner of the photo below. The model Earth, pictured above with the other terrestrial planets, is 10 inches in diameter. How large is the model Sun in the Hayden Planetarium? How large are the other modeled planets? How might you calculate these things? If you were to build your own model of the Solar System, the first piece of information that you would need to gather would be sizes of the astronomical bodies. One of the easier ways to think about the sizes of the bodies is in terms of diameter. What are the approximate diameters of the Sun, planets, and Moon in our solar system? Use the internet or another reference tool to find these diameters. Once you have the approximate diameters of the bodies in the Solar System, determine how to model the Solar System physically in the classroom. The table on the following page provides objects and approximate diameters to help create your model. Astronomical Body Diameter in miles Sun Mercury Venus Earth Moon Mars Jupiter Saturn Uranus Neptune Photos: Hayden Planetarium Leading Question What objects found in everyday life might be most helpful in your model? What object would you choose to represent the Earth? Jupiter? The Sun? Are there other objects that you might add? 12
Student Name: Date: Everyday Objects with Approximate Diameters Possible Objects to Use Approximate Diameter Possible Objects to Use Approximate Diameter 0.1 inch 0.2 inch Plasma Ball 0.3 inch Hamster Ball 7.5 inches 0.4 inch Crystal Ball 8 inches Marble 0.5 inch Volleyball 0.6 inch Honeydew Melon Tolley Marble 0.75 inch 10 inches Black Grape 0.8 inch 12 inches Gnocchi 1 inch Basketball Golf Ball Beach Ball 20 inches Racketball Ball Bean Bag Chair 4 feet Bouncy Ball 2.5 inches Wrecking Ball 6 feet Tennis Ball Water Walking Ball 6.5 feet Baseball Times Square New Year s Eve Ball Orange Tempietto of San Pietro in Rome 15 feet Bocce Ball 4 inches Large Cannonball Concretion 18 feet 5 inches 40 feet Medium Medicine Ball 6 inches Epcot Geosphere 165 feet 1939 New York World s Fair Perisphere 180 feet 1. If the Sun were to be represented by something with a 40-foot diameter, what is the model s scale? Show your work. 13
Student Name: Date: 2. With the scale found in question 1, what everyday object would represent the Earth? The remaining seven planets? The Moon? Show your work. Model Scale #1: Planet True Diameter Scale Diameter Everyday Object Diameter Sun 864,327 miles 40 feet Mercury Venus Earth Moon Mars Jupiter Saturn Uranus Neptune 3. What flaws does this particular scale have? Is it possible to create this model in your classroom? Why or why not? If not, how might you alter your scale so you could use things you can represent in the classroom? 14
Student Name: Date: Recall from the last class what problems your scale might have had. What might you do differently so that your scale uses objects that you can use in the classroom? Model Scale #2: Planet True Diameter Scale Diameter Everyday Object Diameter Sun Mercury Venus Earth Moon Mars Jupiter Saturn Uranus Neptune 4. How does your new model compare to the first one? Is it smaller or larger in scale? Which aspects of the first model are better than the second? Which aspects of the second are better than the first? 5. Can you create a model that incorporates the best qualities of the first and the best qualities of the second model? Fill in the table on the next page with your new model scale. Compare with your classmates and see if you can find the best possible scale. What qualities should the best scale possess? 15
Student Name: Date: Model Scale #3: Planet True Diameter Scale Diameter Everyday Object Diameter Sun Mercury Venus Earth Moon Mars Jupiter Saturn Uranus Neptune Now consider the mean distance of each planet from the Sun (exclude the Moon now). Search for the values of the average distance between the planets and the Sun, and see if you can incorporate this into your model. Is the scale also appropriate for your ideal model chosen in the last question? Model Scale #4: Planet True Mean Distance from the Sun (millions of miles) Scale Mean Distance (miles) Scaled Mean Distance (feet) Scaled Mean Distance (inches) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune 6. Using this scale, would you be able to see Neptune if you were standing at the Sun? Can you think of a place where you could demonstrate this model? 7. Since the model Earth at Hayden Planetarium is 10 inches in diameter, what is the scale that the designers used? How large are the remaining planets and the Sun? 16
Teacher s Guide Possible Solutions Below are three possible scales that your students might use. Celestial Body Scale 1: (1/10^8):1 Scale 2: (1/10^9):1 Scale 3: [1/(2.5x10^7)]:1 Object Diameter Object Diameter Object Diameter Sun Hot Air Balloon 40 feet Bean Bag Chair 4 feet World s Fair Perisphere 180 feet Mercury Golf Ball 1.7 inches English Pea 0.2 inches Hamster Ball 7.5 inches Venus Bocce Ball 4 inches Raisin 0.4 inches Basketball 18 inches Earth Grapefruit 5 inches Marble 0.5 inches Beach Ball 20 inches Moon Gnocchi 1 inch Nerds candy 0.1 inches Grapefruit 5 inches Mars Bouncy Ball 2.5 inches Pea 0.3 inches Small Sugar Pumpkin 10 inches Jupiter Wrecking Ball 6 feet Grapefruit 5 inches Large Cannonball 18 feet Saturn Bean Bag Chair 4 feet Bocce Ball 4 inches Tempiette of San Pietro 15 feet Uranus Beach Ball 20 inches Racketball 2.25 inches Water Walking ball 6.5 feet Neptune Basketball 18 inches Golf Ball 1.7 inches Wrecking Ball 6 feet Listed below are objects and diameters that could fill the missing table on the second student page. Possible Objects to Use Approximate Diameter Possible Objects to Use Approximate Diameter Nerds Candy 0.1 inch Grapefruit 5 inches English Pea 0.2 inch Plasma Ball 7 inches Popcorn Kernel 0.3 inch Volleyball 8.5 inches Raisin 0.4 inch Honeydew Melon 9 inches Acorn 0.6 inch Small Sugar Pumpkin 10 inches Golf Ball 1.7 inches Watermelon 12 inches Racketball Ball 2.25 inches Basketball 18 inches Tennis Ball 2.7 inches Times Square New Year s Eve Ball 12 feet Baseball 2.8 inches First Modern Hot Air Balloon 40 feet Orange 3 inches Epcot Geosphere 165 feet 17
Teacher s Guide Extending the Model Visualizing the geometry of the planets is an accomplishment. For further work, you may also be interested in looking at the numbers and plotting them and to see how various properties of the planets might be related. The geometry so far has warned us that this will be difficult since the diameters of the four smallest planets and the diameters of the four largest form two clusters that are quite different in diameter. The mean distances from the Sun also span quite a large range and seeing any patterns on a regular piece of graph paper will be difficult. A mathematical device that makes it easier to see the behavior of numbers spread widely is to plot logarithms of the numbers rather than the numbers themselves. For any set of data that varies over many orders of magnitude, such as the planets, the energies of earthquakes, or the annual incomes of families, plots of the logarithms of the data tend to be very helpful. When you look at the diameters and the mean distance from the Sun of the various planets and plot them on log-log paper, no pattern becomes immediately evident. There would be a purpose in doing this primarily to obtain yet another set of data about the planets the time it takes each planet to complete one revolution about the Sun. The unit in which this typically is measured is the time it takes the Earth to do this, namely one Earth year. Take the data for the mean time of revolution of each planet and list them next to the mean distances from the Sun. The sensible thing to do is to plot these on log-log paper. You re able to see one phenomenon right away: the two sets of data move up together. A closer look at the log-log plot shows that the numbers seem to fall very close to a straight line. This means that for each planet, the logarithm of y, the period of revolution, is linearly related to the logarithm of x, the mean distance from the Sun. The form of the mathematical equation that these data seem to tell you is log y = a log x + b where a and b are numbers we can read from the graph. If you measure the difference in x and y between Mercury and Pluto (when plotted, of course) you should get about 8.2 cm and about 12.3 cm, respectively. The slope of the line is very nearly 1.5 (or 3/2). This says that log y = (3/2) log x + b or log y 2 = log x 3 + 2b which gives y 2 = Bx 3 with B = 10 2b. What this shows is Kepler s Third Law the square of the period of revolution is proportional to the cube of the mean radius of the orbit. If students are intrigued by logarithmic plots, they may want to investigate the Richter Scale for earthquakes or the loudness of sounds at various distances. 18
Teacher s Guide Extending the Model Planet True Mean Period of Distance from Revolution the Sun around the Sun (millions of miles) (Earth Years) Mercury 36.0 0.241 Venus 67.2 0.615 Earth 93.0 1.000 Mars 141.6 1.881 Jupiter 483.6 11.863 Saturn 886.5 29.447 Uranus 1783.7 84.017 Neptune 2795.2 164.791 19
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