From the Earth
to the Moon

Objective

In this activity, the cadet will get a better perspective of the size and distances of objects in our solar system.  The cadet will also explore the relationships between the Earth and Moon by comparing their relative size and by determining the distances between them.

This is a fun and extremely easy exercise to do, using very common materials.  Preparation time is minimal.  Cadets should be able to repeat this exercise for other cadets, their friends, their schoolmates, or their parents.

Time Requirement

About Fifteen Minutes

Materials

• A Basketball

• A Tennis Ball

• A piece of string or yarn, that you have previously measured to be exactly 9.5 times around the basketball and cut to length

• Masking Tape

• A pen for writing on the tape

Background

• The Earth is about four times larger than its moon

• The diameter of the Earth is about 8,000 miles

• The diameter of the Moon is about 2,000 miles

• The circumference of the Earth is about 25,000 miles

• The distance from the earth to the Moon is about 240,000 miles

Procedure

1. The demonstration area should be at least 30 feet long.   (If the classroom is not that large, try to position yourself so that you can "spill out" into the hallway or outdoors to a length of about 30 feet.   This works great!)

2. Have one cadet hold the basketball, and have another hold the tennis ball.

3. The Aerospace Education Officer (AEO) should state the following introduction (exact wording isn't critical, introduce the concepts of scale!)   "The Earth is 8,000 miles in diameter.  The Moon is about 2,000 miles in diameter.  That makes the Moon's diameter 1/4 the size of the Earth's.  The difference in size can be compared a basketball and tennis ball.  A standard basketball is ten inches in diameter, and a tennis ball is two-and-a-half inches in diameter.  As you can see, this basketball is about four times bigger in diameter than the tennis ball, so these serve as pretty good models for the Earth and the Moon."

4. The AEO states "Okay, we have a model of the Earth and the Moon to scale.  I want you to think about how far apart the Earth and the Moon are, on this same scale."

5. At this point, you're going to need some space, so move to the hallway if necessary.

6. Have the cadet with the tennis ball place it right next to the basketball.  Keeping the basketball stationary, have the cadet with the tennis ball start backing away from the basketball. 

7. Tell the assembled cadets "When you think that the tennis ball is the right distance from the basketball to represent the actual scale distance from the Earth to the Moon, call out "STOP!"  The cadet with the tennis ball will stop, and you can mark your spot on the floor with a piece of masking tape.  Write your name on the tape, and then say "GO!" to the moon-cadet."  (When I've done this, it's pretty common for the guesses to be anywhere from a few inches to a few feet from the basketball...)

8. Once every cadet has made their guess, remove the bundle of string from your pocket, and say "I measured this string to be the correct distance.   Let's see how long it is."  It's a great effect if you just drop this mass of string on the floor - look for bulging eyes in the cadets!

9. Tape one end of the string to the basketball, and then start slowly walking out the distance.  Look down at the floor as you go, and call out the names on the tape-marks on the floor, if you like...  "Cadet Jones said it was THIS far..." which usually gets a response like "Oh, MAN!" from each cadet as you pass their mark.

10. Once the string is drawn out taut, the tennis ball is called to the scene, and placed at the end of the string.

11. It's always great to call out the name of the person who provided the closest guess...

12. Make the announcement "If the Earth was the size of a basketball, and the Moon was the size of a tennis ball, they would be about this far apart.  Think about the Moon orbiting the Earth, and making one lap at this distance every month.  Now, look at how far this is, and picture the Apollo spacecraft making that trip - from the Earth to the Moon - hitting the tiny Moon - a moving target!"

13. If you wandered out into the hallway, you may now return to the classroom, carrying the Earth, Moon, and String.  (It's sometimes fun to leave the tape on the floor until after the meeting, so that cadets can show their parents how they did!)

14. Write down the statistics from the "Background" section above on a chalkboard or white board so that the cadets can see the numbers.

15. Introduce the concept of Pi - it should be familiar to the older students - to explain that the Earth is 8,000 miles in diameter, and 25,000 miles in circumference.  Explain these terms if you need to.  Proceed to the discussion section, quiz the cadets, and perform your dramatic exit.

Discussion

The Aerospace Education Officer should ask the following questions:

• How far away is the Moon?

  • 240,000 miles
    

• What is the approximate circumference of the Earth?

  • 25,000 miles
    

• What is the approximate diameter of the Earth?

  • 8,000 miles
    

• What is the approximate diameter of the Moon?

  • 2,000 miles, or 1/4 the size of the Earth
    

• From these answers, the AEO should ask, "Based on the correct answers to these questions, how many times will the string go around the Earth to equal the distance to the moon?"  (Solution: Divide 240,000 by 25,000 and get approximately 9.5!)  Stuff the tennis ball in your pocket, wrap the string around the basketball (nine and a half times) and walk out...

Adapted from: Aerospace 2000, Volume 1
Published by the Aerospace Education Training Directorate
National Headquarters, Civil Air Patrol.