Lunar and Planetary Institute

How Far is the Moon?

Students gain a better perspective on the relationship between the size and distance of the Moon.


The Activity

Show the students a basketball.  Tell the students that the basketball represents the Earth.  Ask them to compare the Earth to the Moon.

The Earth is 7921 miles wide, and the Moon is 2159 miles wide.

Now ask one student to hold the basketball and another to hold the tennis ball.  Ask the class how far apart the two balls should be to represent the actual distance of the Earth and Moon.  Take a variety of estimates.

Take out the string.  Have the students with the basketball and the tennis ball each take one end of the string and walk apart until the string is at its full length.  Share the answer: if the Earth was a basketball and the Moon was a tennis ball, they would be 23.5 feet apart.  The Moon orbits approximately 238,500 miles from Earth.  (It actually ranges from 225,600 miles to 251,800 miles.)

Does the answer surprise the students? 


Have the students try to imagine how small the Moon actually appears in the sky.  If they extended their arms and closed one eye, would they be able to cover the Moon up with one hand?  One finger?  (It would take less than the width of their smallest finger to cover up the Moon.)  Have them go outside and try it!