By Stacy Palen

You may have noticed that, by now, we have acquired quite an enormous catalog of materials for teaching astronomy. There are so many different pieces, in fact, that even I sometimes find them overwhelming or forget that I did something! I find it useful, then, to pick a couple of topics to focus on each semester. For each one, I put together a series of materials that aims to touch on all the bases for students as they approach the topic. These materials must be intentional, transparent, flexible, coherent, and equitable. In other words, they have to meet the needs of students where they are—not where I wish they were—and help bring students towards mastery, no matter what background they may have.

This semester, I was thinking about parallax. When I meet with students in the classroom environment, I often revisit this concept several times during the semester, giving them a nudge to remember how we measure distance, so that when we arrive at the distance ladder later, they haven’t forgotten this fundamental rung. But in the online environment, I find this sort of “callback” to be much more difficult to arrange. So from the very large catalog of items relating to parallax, I have pulled together six pieces that introduce and teach the concept, assess and refine student understanding, and then ask students to take their knowledge further.

First, in my introductory video for the chapter about stellar properties (Chapter 10 in Understanding Our Universe), I ask students to do the same classroom demo that I ordinarily do: sticking their thumb in front of their face, moving it forward and back, and blinking one eye and then the other. This gives them an intuition for how parallax works and also gives them a way to test their comprehension later; if their answers imply that the object will appear to move more when it is farther away, I can ask them to remember “the thing with your thumb.” My kinesthetic learners really appreciate this.

Next, I ask students to read the chapter, paying close attention to the parallax figure. I do this in my introductory video, and then I have SmartWork questions attached to this concept in their homework to give them a further nudge to do the necessary work of reading the chapter. Some students learn really well in the traditional format of reading and answering questions.

The “Astronomy in Action” video is also in SmartWork—with questions—and shows this concept from a different perspective. Students who learn best by watching demonstrations find this video really helpful. It also helps them with a course-long project of learning how to switch perspectives from the “inside looking out” to the “outside looking in.”

At the end of the week, students do the Learning Astronomy by Doing Astronomy exercise about parallax (Activity 19 in the Second Edition). I have a very short (3 minute) video for each activity, which some students watch. In this video, I recall the thumb exercise and remind them to think about whether more distant objects move more or less. The activity itself also ties back to the demonstration that asks students to use their thumbs and also reminds them of the figure from either Understanding Our Universe or 21^st Century Astronomy.

The following week, I have a follow-up question about the image of Alpha Centauri in Chapter 10. I ask students whether this distance could be measured by parallax and how they would know. There are a couple of ways to answer this question, depending on how well they understand the concept. I’m always impressed by the students who explain that since this is the closest star, and we can measure the parallax for many stars, then of course we can measure the parallax for Alpha Centauri. Other students calculate the parallax angle and compare it to the smallest measurable parallax, while others look it up on the Internet. In any case, I get a sense of how they are thinking about the topic.

Finally, each week, we have a discussion question in Canvas, which is open-ended and speculative. I call them “What If?” questions. The parallax-related discussion question is about measuring the distance to stars that appear to be associated with one another in the sky. I’m asking students to take the concept just a little further by having them think about how knowing the distance helps us figure out how stars are distributed in three dimensions. For some students, this speculative discussion is the best thing that happens to them all week, and they get super into it. Others, naturally, post a sort-of-related answer that they didn’t think hard about. That’s fine, because one of the other things that I’ve asked them to do might be more their “thing.”

Surprisingly, even though there are already six different pieces to this instructional map, I have left out some other things that I could have done—for example, I have a news article about parallax that I could have asked students to read. But I don’t feel compelled to have them do every single thing they could do. Instead, I try to pull together a set of materials that gives them different ways to attack the concept, test their understanding, and then further refine and extend their knowledge.

Do I think this hard about how I assemble the teaching materials for every topic? Not yet...but I’m getting there. I find it really fun to think about how to put different pieces together to build a module that has maximum impact; it’s kind of like playing with Legos, but for teachers!