Scale Model of the Earth-Moon System

In order to make them fit onto a page, diagrams often depict the Earth and Moon as being very close together. To help my students see the correct size and distance relationship, I tape a scale model of the two onto a wall in my classroom.

1. Using construction paper, draw a circle that with a radius of 5 cm. Cut the circle out. This will represent the Earth.

2. Draw another circle with a radius of 1.35 cm, and cut it out also. This will represent the moon.

3. Tape the two circles to the wall, positioning them 3 m apart. This "3 meters" represents the average distance between the Earth and Moon (230,000 miles). Point out that this distance can vary by as much as 31,000 miles, or 40 cm on the scale used for this model (20 cm closer, or 20 cm farther). The model should help students keep the Earth and Moon in perspective as you teach them about phenomena such as tides, phases, and missions to the moon.

As the Appollo missions left the Earth's orbit and headed to the Moon, their speed was about 24,000 miles per hour. The engines were off. By the time they reached a point 30,000 miles from the Moon (37 cm from the model Moon), they had slowed to 2,000 miles per hour. From that point on, they began to speed up once again. The reason for this is that, at first,the crafts were slowed by the pull of Earth's gravity. That point (30,000 miles from the Moon) is where the pull of the Earth and the Moon are equal. Once past that point, the crafts began to speed up once again because of the net force caused by Moon's gravity.

Another interesting exercise is to look at some distances compared to a standard globe (2 cm = 500 miles).

1. The Moon would be about 13.9 cm in diameter. . . about the size of a softball.

2. The Moon would be 15.44 m from the globe.

3. Geosynchronous satellites would orbit 143.4 cm above the globe's equator.

4. About 99% of the atmosphere is within 32 km of the Earth's surface. The atmosphere would only be .13 cm thick!

5. Mt. Everest would be .035 cm high. . . about one-third of a millimeter!

6. The space shuttle would orbit about 1.6 cm above the globe.