the STEM zone
By Dr. Daniel Barth
Earth-Moon model has lots to teach
The first step to understanding a solar eclipse is
to understand the Earth-Moon system. Textbooks
and websites generally do a poor job of this; the
relative size of the Earth and Moon are often shown
incorrectly and the scale of the distance between
them is usually wildly off.
It is the distance between Earth and Moon that is
the hardest to show in a text, on a poster or on a
computer screen. The Moon is about 30 times farther
away than the Earth is wide – make your drawing
of the Earth and Moon small enough to show the
true distance between them and you cannot see any
features that you can recognize.
What you need: Our solution is to have the students
construct a model of a reasonable size,
• Paints and
one that will fit in a classroom, and then
brushes, or
let the children play with that model
to help them understand the relative
permanent
size – and distance – of the Earth and
markers
• Sidewalk chalk the Moon. You can make this model in
a couple of sizes, you can decide which
• 3-inch rubber
one is right for your classroom!
T-ball
The smaller version uses a rubber
• One standard
T-ball for the Earth and a standard glass
glass marble
marble for the Moon. This model uses
or .75-inch ball
7.5 ft of string to connect the Earth and
bearing
Moon together and the model will store
• Spool of strong nicely in a 1-g allon plastic storage bag.
This size is small enough that you can
twine or string
play with it in an empty room or even in
• Super glue or
a school hallway, the Moon’s orbit will
hot glue
be 15 feet wide.
• Flat blue spray
The larger version uses a school
paint
dodgeball (or a basketball) for the Earth
and a rubber T-ball for the Moon. This
larger version uses 30 feet of string to connect the
Earth and Moon and will store nicely in a plastic
grocery bag. The advantage of the larger size is not
only that it is more impressive to your students (the
Moon’s orbit is now 60-ft wide!), but the Moon
and Earth are now large enough to be painted
and decorated to make the model more realistic.
Playing with this model requires an empty cafeteria,
gymnasium or an open school yard.
This article will take you through making the
smaller model, but there is really no difference
42
COURTESY OF L. Eric Smith III
In the smaller version of the model, the Earth is represented by a
rubber T-ball. In step one of the process, a teacher or other adult
should cut a half-inch-deep X into the 3-inch teeball using a utility
knife.
between the two except for the balls that you use and
the length of string.
Materials involved in making the smaller model
include: classroom paints and brushes, markers
sidewalk chalk, a 3-inch rubber T-ball, a standard
glass marble or .75-inch ball bearing, a spool of
strong twine or string, strong glue or hot glue and
flat blue spray paint.
In this model, the larger T-ball will be our Earth and
the marble will be our Moon. Note that the 4:1 size
ratio between these balls reflects the true scale of the
size of the Earth and Moon in space! Because there
is cutting involved, adult supervision is necessary.
Sky ’ s
Up
To build the model:
1. A teacher or other adult should
cut off 8 feet of cord and tie a large
knot in one end of the cord. Use a
hobby knife or small kitchen knife to
cut an X about half an inch deep into
the rubber T-ball. Squirt a generous
amount of super glue into the X, then
use a screwdriver or popsicle stick
to force the knotted end of the string
into the ball.
If you are using hot glue, force the
string in first, then force the nozzle of
the hot glue gun into the hole and fill
with hot glue.
2. Go outside and use the blue spray
paint on the T-ball. Use several thin,
even coats – a heavy coat of paint
will not look good. Place the ball on
several large sheets of newspaper – a
garage is a good place for this. You
will have to spray one side, let it dry
thoroughly, then roll it over and spray
the other side. The final result will be
much nicer if you take your time with
this step.
3. Use a drop of super glue or hot
glue to attach your Moon marble to
the eraser end of a pencil.
4. Measure the cord and put a mark
7-feet, 6-inches from the T-ball. Tie
the pencil with the Moon marble
attached at this location to show how
far away the Moon is from our Earth.
Now that the model is built, it can be
decorated. Children can try to make
a “realistic” Earth if they wish with
all the continents, but they shouldn’t
worry if their “Earth” doesn’t look a
thing like our home planet. It won’t
change how the model works at all!
The little marble Moon can be
painted white if possible – a teacher
or adult can do this with spray paint.
Once the paint is dry, children can
decorate it with a marker and draw
craters on its surface.
Now that our model is built, we can
do several activities with it, most of
these require lots of space so it is
best to use a large open area such as a
playground or park.
Sky ’ s
Up
Left, if you are
using hot glue to
secure the twine
to your “Earth”,
insert the knot
into the X and
then have an
adult insert the
nozzle to fill the
space around
the knot. Below,
once your Earth-
Moon model is
complete you
can use it for
a number of
activities.
COURTESY OF L. Eric Smith III
COURTESY OF L. Eric Smith III
43