The purpose of this phase is to encourage students to apply and extend their understanding of the idea of scale models to encompass the more “far out” scale of the Earth—Sun comparison (and if desired to include a preliminary look at broader range of scales within our solar system and out to the ends of the known universe). These ideas will be further developed both mathematically and in terms of empirical scientific evidence during Earth and Space Science lessons across grades 6-9. The ELABORATION phase serves as a formative assessment to help both students and their teacher determine whether the basic objectives have been achieved prior to a summative assessment that assigns grades to students.
Remind students that their explorations to date have focused on the Earth—Moon scale without considering the size of the Sun on this same scale. Holding up the Earth—Basketball model (or an Earth Globe of approximately the same size), ask students to estimate what they think the diameter of the Sun would be on this same scale. After recording their ideas (which are most likely to grossly underestimate the relative size of the Sun, use one or more of the Internet sources cited in the Materials section to convey visually the idea that 100 Earths could fit across the diameter of the Sun! This is surprising to students who are used to seeing a noonday sun that appears to be approximately the same size as a full moon. (Note: The concept of interplanetary and astronomical distances requires a mathematical understanding of exponential notation (or powers of ten) and is reserved for later grades. Representing both the relative size and relative distances on the same scale is not possible within the confines of a two-page spread in a textbook (though the Earth—Moon system can just fit on a diagonal of a two page spread).
While Internet sites like Suntrek show the relative size of the Earth and Sun in two dimensions on a relatively small scale, it is important that students experience this relationship on a larger scale that they develop in a manner similar to their previous work with the Earth—Moon model. Several options are available for them to further explore:
A blended two-three dimensional model of the relative size of the Earth—Sun can be displayed on the school football or soccer field using the Basketball/Earth (d = 24.2 cm) and a meter stick (or tape line) to measure out (and mark with chalk) a “solar” circle that has a diameter of 24.2 meters (or 2,420 cm or ~ 26.5 yards!). The whole class should distribute themselves around the circumference of this circle to get a better sense of the relative size: 100 Earth diameters ~1 Sun.
A fully 3D model of the relative size of the Earth—Sun can be displayed in the classroom using a large exercise/fitness ball or large balloon as a model of the Sun. Depending on the diameter of the ball or balloon that is selected, students should be challenged to find an everyday object (e.g., ball bearings, standard or oversized marbles, and so on) that is approximately 1/100th of that size to represent Earth on that scale. Note on this same scale, the Moon would once again be 1/4th the diameter of the Earth!
If desired, the teacher can use segments from one or more of the following Internet simulations or supplemental activities to impress on students: (a) the excitement of our journeys to the Moon and how they were achieved by collaborative teams of mathematicians, scientists and engineers; and (b) how truly “far out” our solar system is even though it is only a tiny little portion of the Milky Way galaxy that is a tiny portion of the known universe.
(Note: the power of ten (10x) idea can be thought of an extension of the metric system (e.g.,
1 mm (=10-3 m) à10 mm =1 cm (=10-2 m) à 10 cm = 1 dm (=10-1 m) à 10 dm = 1 m (=100 m). The Common Core State Standards- Mathematics recommends that exponential notation be first introduced in 5th grade. Use of the metric units of mm, cm, dm and meter for making actual measurements in this 5E mini-unit and the video clips cited above demonstrate the need for students to greatly “expand” their previous conceptions of “big.”)