by

Kenneth Fuller

This activity will help a
student of any age develop a clear comprehension of the distinction
between the rotation of a planet and its revolution, and their
relationship to days and years. Also, it will clarify the
complex
explanation of why the time it takes for a planet to rotate once on its
axis is not the same as the length of one day (from noon to noon) on
that planet. ( see myths )

Needed: A circle drawn on the play ground is preferred, if necessary a circle in the classroom will have to do.

Select a reference direction, it may be a direction like north, but preferably toward a fence or wall.

Procedure:

1. Place a student in the center of the circle to play the part of the star. (Sun is the name of a star)

2. Place one student (or more) on the circle (orbit) to play the part of a planet (Earth is the name of a planet), to simplify our example we will use only one, but many can participate at the same time.

3. Have the student on the circle face in the reference direction to begin. For convenience, this should be the place on the circle where the reference direction is also directly facing the student in the center (this is "noon" of day zero), unless of course if you have more than one student on the circle at the same time.

4. Have the student on the circle turn (rotate) counterclockwise one complete rotation (until facing the reference direction again), at the same time moving (revolving) counterclockwise one quarter of the way around the circle. (See the diagram below.)

5. Have the student count one on the left hand, for one rotation.

6. The student continues rotating and revolving along the second quarter of the circle until facing directly at the student in the center ("noon" of day 1).

7. Have the student count one on the right hand, for one day.

8. The student continues rotating and revolving all the way to the starting position, counting rotations and days along the way.

9. The student records the total numbers of rotations and of days in one revolution.

Once students understand how the activity works, several at a time can be spread around the circle rotating and revolving together. Be sure that each and every student has a turn being a planet. When it is clear that they understand that 4 rotations per revolution make 3 days per revolution (year), continue.

10. Have them try zero rotations, always facing the reference direction while revolving around the circle.

11. Have them try one rotation, always facing the student in the center while revolving around the circle.

12. If time and interest permit, let them try other numbers of rotations per rotation.

It would be a bit much to try 366.25 rotations per revolution, But students should now be able to explain why it makes 365.25 days per year.

And they should be able to explain why the average length of a day on Earth is 24 hours when one rotation takes only 23 hours and 56 minutes.

(See the law of planetary days and years. )