# A Model of the Earth and Moon

It is really hard to get an idea of how large outer space is. Our planet is really a tiny ball in a huge universe. The ESP Web site has a page on making models of the Solar System. This time, lets make a scale model of just the earth and moon.

How Big Are They?
If you look up how big the earth is, you will find that the diameter of the earth is about 12,756 km. That means that if you could measure from one side of the earth, right through the center to the other side, it would be 12,756 km. If you did the same thing for the moon, the measurement would be 3476 km.

If you know how to do long division, you could divide the diameter of the earth by the diameter of the moon to find how their sizes compare. The answer is about 3.7. That means the diameter of the earth is almost 4 times the diameter of the moon. If you have a globe at school or at home, measure its diameter. A model of the moon to go with the globe would have to be ¼ the size of the globe.

How Big Should the Model Parts Be?
That would mean a nine inch diameter globe would need a moon that was about 2 ¼ inches across, a little smaller than a tennis ball. An eight inch diameter globe would need about a 2 inch diameter moon. A twelve inch globe would need about a 3 inch moon, about the size of a baseball (hardball). If you have some clay, you could make a ball the right size for your globe. If not, maybe you could crumple up some paper and wrap it with masking tape to make the right size model of a moon for your globe.

How Far Apart Are The Earth and Moon?
How far from the globe should you put your moon model? The real moon is about 384,000 km from the earth. How does that compare to the size of the earth?

You can find the circumference of your globe by wrapping a piece of string around it once and measuring the length of the string. If you did that with the real earth, the measurement is about 40,090 km. How does the measurement around the earth, its circumference, compare with the distance to the moon? With long division, we can find out.

How Far Apart Should Your Model Parts Be?
If you divide the distance to the moon, 384,000 km by the measurement around the earth, 40,090 km, you get about 9.5 times. The distance from the earth to the moon is about the same as 9 and ½ times around the earth. So, if you could wrap a piece of string 9 and ½ times around your globe, that would be how far away your moon model should be from your globe. Try it. Does this look like a long distance to you? Are you surprised?

Finish The Model
Now put your moon and earth model together by putting the globe and the right sized moon 9 and ½ earth circumferences apart. Are you surprised at the way the model looks?

Visit our Web page on the moon for help in learning more about our closest neighbor in space.