Sky's Up July-September 2017 - Page 42

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