### by Daniel Perley, Astronomy

#### Teaching Effectiveness Award Essay, 2006

Astronomers are confronted by a pair of obstacles when studying the universe: things are far away, and they take a long time to happen. These facts present no less a challenge when teaching students about astronomy in the classroom. Crunching down 1070 cubic miles of space and 14 billion years of cosmic history into a room forty feet on a side in a one-hour lesson is no small task.

Our solar system is certainly much smaller than the universe as a whole, but no less of a challenge to visualize. At the start of one semester last year, I asked students to produce, using a table of facts and figures, a scale-model diagram of the solar system. I was exasperated to see each group placing all the planets in a perfect line, with their radii so huge they practically touched despite my cautionary notes on orbital positions and the planets’ true sizes.

This illustrates the major challenge in picturing the solar system: in accurately presenting one scale, one must necessarily misrepresent another to correctly diagram the solar system, the planets would vanish into specks. Even worse, however, is that diagrams and scale models of this sort are necessarily static. The planets don’t just hover in space in a line but actually move, following the mathematical laws of Newton and Kepler that form the bedrock of any astronomy class.

It is tempting in such cases to forget the subtleties and call it a victory if students remember the order of the planets and know that they all orbit the sun in (almost) circles in (almost) the same plane. However, the details can become essential: not just the mathematics of orbits, but also subjects as diverse as seasons on Mars, the classification of Pluto, the detection of extrasolar planets, and many other topics all require a fairly sophisticated picture of the structure of the solar system to fully grasp.

In this case, words and diagrams were the problem, and no amount of them would solve it. My solution, instead, was to produce for my students an animated simulation of the motion of the planets around the sun, and display it on one wall using an LCD projector. I allowed students to run the laptop’s controls, giving them the opportunity to zoom in (to see the size of a planet) and then zoom out again (to see the whole, moving system) in one, continuous comparison, or to change the viewing angle of the camera. Furthermore, students could physically see the planets in motion in their orbits, from Mercury through Pluto.

Once students appreciate these basics, it is a small step to begin to understand the subtleties. See how Mercury is racing around the Sun frantically while Neptune barely budges? That’s a consequence of Kepler’s third law — something the students could (and did) easily show quantitatively by timing the length of each planet’s orbital period, then comparing to their distance from the Sun as measured by a meter stick and a scale bar. Many other orbital laws could be dealt with in an equally visual, direct manner. Even though the section allowed only 50 minutes for the whole activity, the amount of material I was able to present with this one simulation was remarkable.

I set out to gauge the effectiveness of this exercise (and several others) at the end of the semester by having my students fill out a short survey, rating each activity on a scale of 1 to 5 based on whether it was interesting and whether it was useful. Students gave the orbital demo very high marks: an average 4.1 on the interesting scale, the second most-popular activity all semester in that category, and a 4.3 in usefulness, ranked third. Clearly, students not only found the activity useful for studying for their upcoming midterms, but also found it held their attention, and remembered it many months after the fact. The lessons of this were clear: the challenge, now, is to find ways to incorporate more dynamic computer activities into topics beyond our own solar system, to the rest of the universe.