Target Age Group
Elementary

Ojbective
Students will understand the distance between the Earth and the Moon

You will need
basketball, tennis ball, string about 30 feet long (keep string in your pocket at first), marking pen, unsuspecting friends

What to do
1. Say to your friends, “Did you know that if the Earth was the size of a basketball, the Moon would be the size of a tennis ball? How far away
do you think they would be from each other?” Pass the balls to your friends and give them some time to think.

2. After your friends show you what they think the distance is, it is time to pull the string out of your pocket. You can say “Ta Dahh!” if you like, but they may say, “Hey, come on. That’s just a piece of a string.” Ask your friends to wrap the string around the basketball about 9 ½ to 10 times. Before they unwrap the string they should mark the end with the pen so that they can find it easily.

3. Have your friends unwrap the string one time around and then stop and hold that part of the string out away from the basketball. This is the distance of geostationary orbit. (They may say “Huh?” if you say that.) Most communication satellites are located at this distance. If you have a satellite dish for your TV, that’s where it is pointed right now and that’s only 10% of the way to the Moon.

4. Keep unwinding the string. Ask one friend to hold the basketball and the other to hold the tennis ball, keeping one end of the string on the basketball while they unwind.

5. Next, ask the friend with the tennis ball to take the other end of the string and back away from the basketball until you see the mark on the string. Now you can say “Ta Dahh!” because that is how far the Moon would be from the Earth, if they were tennis ball and basketball size. See below to find out how far it really is!

What's Going On?
The Moon orbits the Earth at an average distance of about 30 Earth diameters. The distance around the Earth’s Equator is just under 24,000 miles so ten wraps of string gives a close approximation of the distance . You can also discuss Pi here if you wish to employ Moon Pie pun. Notice that at this scale the International Space Station orbits less than ¼ inch ( 0.63 cm) above the basketball!


The Moon is 240,000 miles from the Earth. When you do this activity, most people find out that’s a lot farther than they thought. Most people also have no idea of the true scale of the solar system. Visit this site for an interactive three-dimensional view of the Earth and all the satellites that surround it. Explore and learn about these satellites that are close to the Earth. Geostationary orbit is the current frontier of commercial activity in space. The Google Lunar X PRIZE will expand that frontier by 10 times.

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