Target Age Group
Middle School

Ojbective
Students will understand the relative sizes of the Sun and planets by converting them to a scale where the Earth is a basketball, the Moon is a tennis ball and they can see and compare these bodies in a parking lot.

You will need
Rope or strong string 43 feet (13.1 meters) long, sidewalk chalk, parking lot, friends, yardstick, marking pen, basketball, tennis ball

What to do
1. Stand at a central point in the parking lot. You are going to need 43 feet of space all around you. To make sure you are at a good spot, hold one end of the 43-foot rope; then have a friend hold the other end and walk until the rope is stretched out all the way.

2. While you continue to hold the rope at your center spot, have your friend walk in a complete circle around you. That complete circle represents the circumference of the Sun.

3. As one friend walks around with the rope, have other friends draw around the circumference with the sidewalk chalk. That is the outline of the Sun.

4. Use the table below to compare the size of the Sun to other planets. Mark the radius of each planet on the long string, find another point in the parking lot to be the center, and walk it around the same way you did for the Sun.

5. How does our Earth-Moon system compare to the size of the Sun? To find out, place the basketball at the center of the parking lot Sun and the tennis ball about 27 feet away.

It’s raining and you don’t want to go outside? No parking lot nearby? Don’t despair. You can do a version of the same activity without leaving your computer, go to the next activity. A planetary radii table for both activities is also on the next page.

What's Going On?
You can find out by going to the Answer Sheet

Download complete guide as [PDF ]