We begin by creating a scaled-down map of the classroom to familiarize students with scaling and distance on a very familiar level. We continue by scaling the size of the solar system and continue this model out to the edge of the local group. Also, in another model the distance to the edge of the known universe is scaled to a comprehensible size by setting the distance between the Sun and the Earth to the thickness of a sheet of paper. It is presumed that students have some knowledge of the planets and workings of the solar system, and also a general idea of the scale of the solar system. This exercise builds on this knowledge and extends it to scale the universe including the nearest star to the Sun, the distance to the center of our galaxy, the diameter of the galaxy, the distance to the next galaxy, the diameter of the local group and the distance to the edge of the known universe.

Tables I, II & III, which are to be used in the activities which follow, show statistics of the planets in metric units, Earth units, and scaled units, respectively. The scaled units are calculated based upon scaling the diameter of the Sun to 3 inches. This convenient size is demonstratable in a large classroom, and also familiar to students as ordinary objects, like oranges or tennis balls. It also allows for conceivable scaled distances to astronomical objects. The first two tables are included mainly for reference and comparison, and to encourage familiarization with scientific units.

Table I. Astronomical Object Properties in metric units

 Mass (kg) Equatorial Diameter (km) Distance from Sun (106 km) Rotation Period (days) Orbital period (years) Sun 1.99 x 1030 1390000 0 Mercury 3.30 x 1023 4,880 58 59 0.241 Venus 4.87 x 1024 12,100 108 243 0.615 Earth 5.97 x 1024 12,756 150 1 1 Mars 6.42 x 1023 6,790 228 1.03 1.88 Jupiter 1.90 x 1027 142,984 778 0.4 11.86 Saturn 5.69 x 1026 120,536 1427 0.4 29.46 Uranus 8.66 x 1025 51,118 2871 0.7 84.01 Neptune 1.02 x 1026 48,528 4497 0.6 164.8 Pluto 1.31 x 1022 2,300 5910 6.4 248 Proxima Centauri 40500000 Distance to Center of Galaxy 2.5 x 1011 Diameter of Galaxy 9 x1011 Distance to Andromeda 2 x 1013 Diameter of Local Group 3 x 1013

Table II. Astronomical Object Properties in Earth Units (based on Earth mass and diameter)

 Mass (Me) Equatorial Diameter (De) Distance from Sun (AU) Rotation Period (days) Orbital period (years) Sun 333000 109 0 Mercury 0.06 0.38 0.39 59 0.241 Venus 0.81 0.95 0.72 243 0.615 Earth 1 1 1 1 1 Mars 0.11 0.53 1.52 1.03 1.88 Jupiter 317.9 11.2 5.2 0.4 11.86 Saturn 95.18 9.4 9.54 0.4 29.46 Uranus 14.5 4.0 19.19 0.7 84.01 Neptune 17.1 3.8 30.06 0.6 164.8 Pluto 0.002 0.18 39.5 6.4 248 Proxima Centauri 270000 Distance to Center of Galaxy 1600 Diameter of Galaxy 6000 Distance to Andromeda 140000 Diamter of Local Group 200000

Table III. Astronomical Object Properties in Scaled Units (based upon scaling the diameter of the Sun to 3 inches)

 Mass Equatorial Diameter (Scaled Inches) Distance from Sun (Scaled inches) Rotation Period (days) Orbital period (years) 0 Sun 3 0 Mercury 0.011 10 ft. 59 0.241 Venus 0.026 19 ft. 243 0.615 Earth 0.027 27 ft. 1 1 Mars 0.015 41 ft. 1.03 1.88 Jupiter 0.31 140 ft. 0.4 11.86 Saturn 0.26 260 ft. 0.4 29.46 Uranus 0.11 520 ft. 0.7 84.01 Neptune 0.10 810 ft. 0.6 164.79 Pluto 0.0050 1100 ft. 6.4 247.69 Proxima Centauri 1400 miles Distance to center of galaxy 8400000 miles Diameter of galaxy 31000000miles Andromeda 730000000 miles Diameter of Local Group 1000000000 miles

Because this exercise concentrates on distance scale, you may want to begin the lesson with an exercise demonstrating the relative masses and radii of the planets. For a good example of this comparison, consult the New Jersey Science Curriculum Framework in the list of learning activities for standard 11 under Planet Gravities. This exercise uses relative numbers of pennies in empty soda cans to represent the weight of a full soda can on other planets. The number of pennies in each can changes based upon how massive the particular planet is and how big its radius is.

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