Solar System Demo: Instructor's Guide

The goal of this activity is to give the students an idea of the size and scale of the solar system and the planets in it. The students should have some background on the solar system (the names of the planets, the order in which they are arranged) and an understanding of what a scale model is. The activity is presented in two parts -- one that demonstrates the distance scale of the solar system, and one that demonstrates the size scale of the planets. Attempting to do both on the same scale is inconvenient because the planets are so small compared to the distances.

The first activity is the solar system distance scale. The instructor should precede this in the classroom by going through the first three questions on the activity sheet interactively with the students. The first question asks them what a scale model is. We usually try to work in some mathematics here, maybe powers of ten type stuff. The second question asks them to compare the distance between the Earth and the Sun to the distance they walk to school every day to get a feeling for how huge it is. The third question asks them to think up a reasonable scale for the model so that it fits on the field next to the school. After this, the students should divide into their groups of 4 or 5 and go outside (make sure they bring a pencil). They should then construct the scale model according to the scale distances given in Table 1 using the small cones. To measure the distances, we suggest that the students count one pace as the equivalent of 1 meter. To ensure that everyone in the group is engaged in the activity, the students should take turns walking the distance to the next planet and reading off the scale from the table.

The second activity deals with the size scale of the planets. Question 5 on the activity sheet asks students to figure out how big the Earth would be on the distance size scale so they understand the relation between the planet sizes and the distance scale. For question 6, each group receives 9 objects of relative size that represent the planets. Using Table 2, which lists the actual sizes of the planets (and the scale sizes), the students should figure out which planets correspond to which objects. The question asks the students to explain how they are making their choices. Finally, the question asks the students to figure out the scale of this second model.

This should be more than enough to fill up one class period, and perhaps two. However, if there is extra time, some supplemental questions are (in no particular order):

• Are the planets always the same distance from the sun? Why or why not?
• Are all the planets in the same plane?
• How do comets fit into all this?
• How long does it take for the Earth to go around the sun? Mercury? Mars? Saturn? Pluto? Do you notice any pattern?
• What keeps the planets from flying off -- why do they keep going around the Sun?
• Explain the presence of the asteroid belt.
• The big planets (Jupiter, Saturn, Uranus, and Neptune) are mainly made of gas (they have small solid cores), but the inner planets are mainly solid. Why? What about Pluto?