# 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)

(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 Post-It 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 pre-conceptions 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 30-50 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 10-15 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 Post-It 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 108 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.

There is also a 7-minute video that can be shown to students (available in YouTube and Vimeo) titled To Scale: The Solar System.