October 5: Retrograde Motion Activity

At the end of the last class, I showed the class retrograde motion using the software (Stellarium), but I did not explain how it happened. I was hoping a few students might think about it outside of class, and perhaps search online for an explanation (there was no indication that anybody actually did this). The idea for this class was to have the students act out the motion of the planets (in groups of four) so that they could directly see how the heliocentric model explains this phenomenon. I assumed it would be obvious to all the students that the geocentric model couldn’t easily explain retrograde motion, and for the most part I still feel this assumption was okay.

The main problem with the activity was that I simply did not spend enough time troubleshooting the writeup. I used way too much text to describe the activity and had no pictures. Some of the descriptions were vague as well. It seemed that most groups gave up trying to understand the activity fairly quickly, and called for my help instead of rereading. I point this out not to criticize them, but as something to keep in mind in the future when planning this sort of activity. Initially, I tried to help groups one at a time, hoping that some would get it on their own and that once I explained it to a group, more questions wouldn’t arise for a while. After getting through three groups it was clear that this strategy was a losing one. At the teacher's suggestion, I gathered the whole class in one spot, picked a few volunteers, and walked everybody through the activity together. This worked fairly well, but I think many got bored and/or weren’t paying attention. After asking for questions, all returned to their groups to try a second time. Most groups got it this time, with a little more encouragement. We went inside and spent the remaining time, about 15 minutes, discussing what happened. I wrote some discussion questions on the board for the students to copy down, but did not have a lot of time to take questions or clarify.

A few changes would make this activity go much smoother. Mostly, rewriting the assignment for clarity, and adding pictures. Better terms should be used for describing positioning and the directions to face. More emphasis on walking around the person acting as the sun, keeping the distance the same by using the rope. Smaller steps should be used so that data points are not so spread out. More thought should be put into the discussion questions, perhaps. Given more time the groups should act out the geocentric model as well so that they can compare the two systems. In the end the activity required twice as much time as planned for. Next time I will start with the demonstration!