Scaling planetary size and the solar system
Learning Objectives
 To make basic scaling calculations, especially relating to the size of and spacing between the planets
 To increase knowledge of large numbers
 To become familiar with the order of planets in our solar system
 To gain familiarity with the metric system (pending method of implementation, use of metric system or not for measurements)
Standards Addressed
(forthcoming)
Supplies/Materials/Articles Needed
Depending upon which method teachers are having students scale the planets/solar system, teachers need to secure a rope, or a roll of toilet paper, or chalk for a sidewalk, etc. The version describe here requires PostIt notes and tape measures.
Preparation Time Needed
Minimal. Teachers should calculate ahead of time the solutions to the scaling exercise, and be prepared to answer why student preconceptions of planetary size and spacing were different from the calculated values.
Class Time Required
Depending upon how many calculations the teachers have the students complete (if any) and the math level of the students, this will determine how much class time is required. If a teacher asks students to make an estimation of the size/spacing of the planets, for example, and then calculate the actual position along a set distance and reposition their estimates, this could take 3050 minutes. If a teacher will be doing an entire class demonstration and not having students complete any calculations, this "show and tell" exercise could take 1015 minutes with supporting lecture on solar system basics.
Activity Description
This exercise challenges students to think about the order of and spacing between the planets in our solar system. Teachers may swap out and complete this exercise by having the students scale the relative size/diameters of the planets. I start by having the students work in groups of four or five and use the length of our classroom as the distance between the Sun and Neptune. Students must discussion and determine where to place a labeled PostIt note on the floor at the approximate relative position of the planet. I then give students the data below with the actual distances and have them calculate (encouraging them to set up a ratio) for the distance along the floor that represents the location of each planet. We then discuss the differences between what they estimated and what they calculated and why their perceptions were different.
Mean dstance between the Earth and Sun is measured in AU (astronomical units). The distance between the Earth and Sun (1 AU) is equal to ~1.495 x 10^{8} km).
 Sun to Mercury = 0.387 AU
 Sun to Venus = 0.723 AU
 Sun to Earth = 1 AU
 Sun to Mars = 1.524 AU
 Sun to Jupiter = 5.202 AU
 Sun to Saturn = 9.555 AU
 Sun to Uranus = 19.218 AU
 Sun to Neptune = 30.109
There are several variations of activities for scaling planetary size and distance that have been classroom tested and shared through the Science Education Resource Center (SERC) and other sources. Teachers are encouraged to check out these adaptations, as a scaling exercise on the planets is extremely useful for students before discussing the solar system.
 How big is the solar system, from the National Optical Astronomy Observatory
 Build a solar system, by The Exploratorium
 Scaling Galileo's Solar System  Size of the Globes, from SERC

Investigating dimensions of the solar system, from SERC
There is also a 7minute video that can be shown to students (available in YouTube and Vimeo) titled To Scale: The Solar System.