Paper Plate Education
"Serving the Universe on a Paper Plate"

Activity: Paper Moons II

The following text was excerpted from GLPA Proceedings, 1993, p. 79; used with permission:

Abstract: A "Hands-on" experience using 2 common materials—(1) Paper plate (2) Football field. The experience addresses a common misconception about the motion of the moon—that the moon "loops" around the earth—when in fact the path of the moon is always concave to the sun! At a distance of 100 yds—goal line to goal line--the plate is about the radius of the moon's orbit, and the width of the field represents about 30o or 1 month.

SPICA Activity:

The Paper Plate meets the Football Field or How the Moon Really Moves!!

1. Have students draw a line representing the motion of the Earth during a time period of 30 days. (Should be an arc similar to 1/12 of a circle.)

2. Have students draw a line representing the motion of the moon during that same period. (Note: If the arcs look similar then there is no need for this lesson!)

3. Most students will make a loop for the moon around the earth during the 30 day period. The misconception is due to out-of-scale drawings textbooks use. To improve students' understanding, make a scale model of the motion.

4. Take students to a local football field. At the center of one goal line place a basketball to represent the Sun. At the other goal line lay a string for the path of the Earth. The ends of the arc should be about 3 yds from the goal line.

5. Take a cheap, handy, 9" paper plate. It is best if each student has one and does the exercise for Hands-On learning. Have the student draw a heavy dot, smaller than the letter 'O' on one side of the plate, and across from it place a small dot (1/4 the size of the big dot). The big one is to represent the Earth and the small one the moon. Keeping the Earth dot on the string, move it along making the moon dot "go around the earth" one time as you cross the football field.

6. Have each student make a drawing of what they have traced on the ground onto a notebook size paper for evaluation .

Extension: Start everyone with the moon toward the Sun and have them mark the phase or draw what the moon will look like at different points across the football field.

Extension: Give students the data and have them construct their own model to scale. Find the slight errors in the model described. Talk about 5 degrees above or below the surface of the field. CAUTION: Do not have the students dig up the field to show this!! Coaches do have more power than science teachers!!!

Extension: Expand the model by making the paper plate the Earth, cut out another plate for the moon, figure out how far away the sun would be at this scale, and do the orbital motion across the long part of the field from goal line to goal line. HINT: About 33 plate diameters to the moon, 400 times that to the Sun

Extension: Barycenter will be a little over 1/3 the way from the edge of the plate to the center of the plate. It is the point that orbits the Sun, with the moon and rest of the earth swinging around the barycenter.

Reference: The Astronomical Companion by Guy Ottewell.

Contributed by Wayne James.

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