Universal Proportions
Overview: Create scale models of Earth, the Moon, and distances in space Learning Goal: Develop a sense of the relative sizes of Earth, the Moon, and of the immense distances within the universe Video Link: New View of the Universe
Introduction
When Edwin Hubble calculated the distance to a variable star, he was astounded to see that it was outside the Milky Way. The universe was far larger than anyone had expected! To give students an idea of the immense size of the universe, have them work in groups of three to model the relationship between Earth and the Moon, and then scale distances within and beyond our solar system. After the activity, show the New View of the Universe video segment so that students can learn more about the people and events that revolutionized our understanding of the universe.
Model the Earth and Moon
Materials for each group:
 three 8 oz. cans of clay (rolled into one ball)
 measuring tape or yardstick
 toothpicks
 Give each group a ball of clay, and ask students to divide it into 51 equal pieces. Allow time for students to figure out how to divide the clay.
 Have students draw upon their existing knowledge to create scale models of Earth and the Moon using the 51 pieces of clay. Students should record how many pieces they use to build each model. Have them record the volume ratio of Earth to the Moon using the number of clay pieces in each model. Compare results.
 Share with students that Earth is about 50 times the size of the Moon, based on its volume. Ask them to regroup the clay in a 50:1 ratio. How do their original models compare in volume to this ratio?
 Now that the models accurately show the relative sizes of Earth and the Moon, ask students to show the relative distance between them. Again, encourage them to use their own intuition and knowledge to decide how far apart to place their models. Have each group measure and compare distances, and discuss their reasoning.
 The mean distance between Earth and the Moon is 384,000 km, and Earth's diameter is 12,756 km. Have students use this information to figure out how far apart to place their models to represent the relative distance between Earth and the Moon. How close were their original estimates?
 The space shuttle orbits at approximately 611 km above Earth. Have students locate the shuttle's orbit based on the scale of their clay models. A toothpick inserted into the clay can show the distance of the shuttle from Earth.
 Where does the Sun fit in this scale model of planetary orbits? Let students know that the mean distance between the Sun and Earth is about 150,000,000 km. Ask students to determine the proper placement of a marker representing the Sun. Would the Sun model be in the classroom?
Scale Distances
Materials for each group:
 butcher paper
 measuring tape or yardstick
 copy of chart below
 The distance from Earth to the Moon is minuscule compared to distances within our solar system and beyond. Give each group a piece of butcher paper (about 1.25 m long) and a copy of the chart below. Have each group create a scale drawing of the solar system showing the relative distance of each planet from the Sun.
 When students are finished, have each group explain its scale. With that scale, can they show the position of the Moon? If not, what scale would work? Then how far away from the Sun would Pluto be?
 Finally, have each group use the scale it established to calculate the length of paper needed to show the distance from the solar system to Alpha Centauri, the nearest star system, 4.3 lightyears away; from the Sun to the center of the Milky Way, 30,000 lightyears away; and from our galaxy to the Andromeda nebula, the nearest spiral galaxy, 2 million lightyears away.
Distances from the Sun
Planet  Mean Distance from the Sun 
Mercury  58 million km (36 million mi) 
Venus  108.2 million km (67 million mi) 
Earth  150 million km (93 million mi) 
Mars  227.9 million km (140 million mi) 
Jupiter  778.4 million km (483 million mi) 
Saturn  1.4 billion km (886 million mi) 
Uranus  2.9 billion km (1.8 billion mi) 
Neptune  4.5 billion km (2.8 billion mi) 
Pluto  5.9 billion km (3.7 billion mi) 
For results for this activity, click here. Physics and Astronomy Program Contents
Looking Back in Time
Atomic Ethics
Stranger than Fiction?
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