Estimation of distance between earth and the moon

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Home : 2002 : January : 11

Estimation of distance between earth and the moon
By Lori 2

I like to have my students estimate the distance from the earth to the moon with this visual representation. Using scale models provides an opportunity to put meaning to astronomical units.

Supplies:

12 inch globe
23
feet of string
tennis ball
scissors
transparent tape
calculator and reference materials, if desired
I do this with older students so they have to do some calculations.
Procedure:
Place or hold the globe in a corner of the room.
Tell students that if the earth was the size of the globe, the moon would be the size of the tennis ball. Ask them to think about how far

apart the moon and earth would be if they were really this size.

Ask a student to place the tennis ball noon at a distance from the globe that represents how far apart the moon and earth are. Or have students stand where they estimate the scale distance.

Tape the end of the string to the equator of the globe. Wrap the string around the globe 3 times. Give students the opportunity to change their estimates of distance. Wrap 3 more times (total of 6 so far). Give students another opportunity to change their estimate. Continue wrapping string around the globe. The string should wrap around the globe a total of 9.5 times. (Note: the distance between the earth and moon is apx. 238,606 miles or 384,000km. The earth's circumference is apx 24,855 miles or 40,000km)

Unwrap the string (keeping the end taped to the Earth's equator) and extend it outward to each person to judge the accuracy of their estimate.

Discuss how estimates could have been modified more accurately. The reason why the string is wrapped around the globe 9.5 times is because we have used the circumference of the Earth to represent our base line distance to the moon. I ask my students to divide the distance between the earth and moon by the circumference of the earth and see how accurate our method of estimation was.

Higher level thinking for older students: How many earth diameters could fit between the earth and moon and why? (answer 24,855 miles (earth's cicumference) divided by 3.14159 (pi) + 7,912 miles (earth's diameter) then 238,606 miles (the distance from earth to the moon) divided by 7.912 miles (diamter of the earth) = 30 earth diamters to go from earth to the moon.

Create a larger model of the distance from earth to the moon. Remember, the diameter of your moon should be 1/4 the diameter of your earth.