202. Planetary Scale

     Everything in a writer’s life is grist for the mill. For a science fiction writer that includes science itself and, in my case, the teaching of science.
     Here is some more teacher geek. In a book on teaching middle school astronomy, this would be an appendix.

When I was in my early teens and discovered the local library, it not only gave me science fiction, but science as well. I remember the dozen or so books on popular astronomy. I particularly remember How to Build a Telescope, which aroused my lust then dumped me when I found out I didn’t have enough money to but the mirror blanks.

The single issue that most challenged the writers of those books was how to convey the scale of things. Now, if you are under forty, you will have to project your mind back to the days when print technology did not include glossy paper and color photography. Visualize a few grainy black and white photos, a few drawings, and lots and lots of words. Like, “If the distance from the Sun to the Earth were equal to the thickness of a sheet of paper, then the distance to Alpha Centauri . . . “

I grew up figuring out that kind of analogy, but if I gave such a book to one of my modern students, their eyes would glaze over and the wheels would stop turning. The children of Sesame Street have to be shown.

Would you like a simple example? Did you know that a softball is moon-size in comparison to a 12 inch classroom globe of the Earth? And if you hold the softball 30 feet away from the globe, it will be proportional in distance as well as size.

For the rest of the solar system, you can’t show both proportional size and proportional distance in a classroom. You can buy a poster with the proportional sizes, but the planets are all on top of each other. If you make a chart of proportional distances, the individual planets will be too small to see.

You can do both, however, if you are willing to take the exercise outside.

We are about to make a model of the solar system. If you want to get out your calculator, be my guest, but I’ve already done the math and I’m willing to share. The scale I used was one to one billion. It would be easier in metrics, but we will eventually be using a local road map for this, so the good ole American system will have to do.

The chart below is in miles and double-steps. That’s because we want your students to get into the act and count the distance to the planets. A double step is normal walking, counting every time your left foot hits the ground, one-and-two-and-three-and . . .

Your sun will be about five feet in diameter. I looked for years for a balloon that size and never found one, so each year I made a new five foot diameter circle of paper and taped it to the outside wall of my classroom. The distances you need are:

Mercury        38 double steps
Venus            71 double steps
Earth             99 double steps
Mars            150 double steps
Jupiter         513 double steps or 0.5 miles
Saturn                                           0.9 miles
Uranus                                         1.7 miles
Neptune                                       2.7 miles
Pluto                                            3.5 miles

You can skip Pluto if you want, but when I first started doing this, it was still a planet.

Give some of your students models of the planets (we’ll talk about sizes below) and take off with the whole class, counting double steps. At 38, leave the student with the Mercury model and continue with the rest of the class. Et cetera.

My double steps go through Jupiter because our playground allowed us to get almost that far. When we reached the boundary fence, I would tell them, “Jupiter is just beyond that house.” Then I would reel off where Saturn through Pluto would be found. My recital would mean nothing to you; you need to make up your own. Find a large scale local map, measure out distances from your classroom, and memorize them. (For us, Pluto was in the next village.)

None of this would be worthwhile without models to show how small our planets are in comparison to the space they inhabit. I made Mercury, Venus, Earth, Mars, and Pluto out of  beads or glass headed pins, stuck into dowels. Be sure to paint the dowels orange for when Johnny loses one in the long grass. The rest of the planets were made of rubber balls found after multiple trips to toy stores, and painted with artists’ acrylics.

You need these sizes, and this time I’m going metric because it’s way easier.

Mercury       5 mm
Venus        12 mm
Earth         13 mm
Mars           7 mm
Jupiter     143 mm
Saturn     121 mm
Uranus      52 mm
Neptune    50 mm
Pluto            3 mm

Feel free to pass this on to anyone who might want to make this model.

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