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