This activity will help a
student of any age develop a clear comprehension of the complex
explanation of why the time it takes for a satellite (Moon) to revolve
once around its planet (Earth) is shorter than one lunar month (new
phase to new phase). Moon completes one revolution around its
orbit in about 27.3 days. Because Earth has traveled
approximately 30o around its orbit in the time it takes Moon
to go from new moon to new moon, Moon must revolve about 390o
to again be in the same direction from Earth as Sun. This
averages about 29.5 days.
Needed: A circle drawn on the play ground is preferred, if
necessary a circle in the classroom will have to do.
reference direction, it may be a direction like north, but preferably
toward a fence or wall.
A ball to represent a satellite.
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
if you have more than one student on the circle at the same time.
4. Have the student hold the "satellite" in front at
5. 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 around the circle.
(See the diagram below.)
6. Each time the student is facing in the reference direction
count one revolution (of the satellite).
7. Each time the student is facing toward the student in the
center count one "new phase" (end-beginning of a month).
8. Even if it is not practical to have the satellite revolve 13
times for each revolution around the planet, as with Earth and Moon, it
be clear that 13 revolutions will make 12 months.
9. Give each student an opportunity to play the planet.