By Tabitha Buehler (University of Utah)

I consider my introductory astronomy class (The Universe) at the University of Utah to be an active-learning class. To me, this means that my students don’t sit and passively listen to a lecture for the entire class period—I sprinkle in activities that engage their senses besides hearing among short bits of lecture. Alongside others, these activities include two-minute writing reflections, think-pair-share clicker questions, group worksheet activities, and get-up-out-of-your-chair-and-do-something activities. My students and I particularly enjoy the latter type, and I try to incorporate them when I feel that we have the time. Two of these activities are what I would call explorations—one of which examines the Earth-Moon distance, and the other the H-R Diagram.

Earth-Moon Distance Exploration

I like to both begin and end the semester of my class with the theme, so eloquently stated by Douglas Adams, that “space is big.” In class, we discuss unfathomably large (and, sometimes, small) sizes and distances that it really gets near impossible to have a feel for the true scale of things. This first-day-of-class activity is an attempt to begin to impress upon students the scale of astronomical sizes and distances.

Supplies needed:

• Cutouts of the Earth and Moon, size-scaled; 1 of each per group

Intended Learning Outcome:

• Relate the size of the Earth, the size of the Moon, and the Earth-Moon distance

I divide my class into groups of four and give each group a cutout of the Earth and a cutout of the Moon. I ask them to do this activity without looking anything up online. I tell my students that the sizes of the Earth and Moon are at the correct scale with respect to each other. I give the groups about three minutes to guesstimate how far apart they think the pair of worlds is with respect to their sizes and to place them at appropriate distances apart somewhere in the classroom. I get a wide range of distance estimates, and, after the students look around the room at the guesses of all of the groups, they are curious to know the answer! I then reveal that the Moon is about 30 Earth-diameters away from the Earth and ask for a volunteer group to set their Earth and Moon at this distance for everyone to see. Most students are surprised at how far apart the Earth and the Moon are.

For remote instruction during the COVID-19 pandemic, I adapted this activity in such a way that it would also be useful to an instructor who wanted to devote less time to it or did not have a large enough space for it. For the adaptation, I created a multiple-choice question that could be used as a think-pair-share activity or could still be discussed and answered by a four-person group. The question asks, “Which of the following images (Figure 1, Figure 2, Figure 3, and Figure 4) best represents the Earth-Moon distance?”

H-R Diagram Exploration

My motivation behind creating this activity was to allow students to discover the elegance of the H-R diagram. This was partly because I wasn’t detecting the same level of excitement from my students that I feel (and try to share) when we would discuss the H-R diagram.

Supplies needed:

• Whiteboard space for each group
• At least one whiteboard marker for each group
• A table that lists stars, sizes (small, medium, large), solar luminosities, and surface temperatures
• Cutouts of circles of different sizes and colors to match the stars in the table; 1 set for each group
• Scotch tape for each group

Intended Learning Outcomes:

• Find the position of a star on the H-R diagram based on its luminosity and surface temperature
• Identify trends in stellar characteristics among a group of stars plotted on an H-R diagram

I have done this activity twice so far, and both times I did it before we had an in-class discussion of the H-R diagram. My students were supposed to have read about the H-R diagram before coming to class that day, but it might be interesting to do this activity before they even do the reading. Either way, it sounded like it was still new enough to my students that they still experienced a nice level of exploration.

I divide my class into groups of four and give them the supplies they will need. I show them this blank plot of an H-R diagram and ask them to recreate it on their whiteboards. I give them about 15 minutes to do this, and, after, I prompt them to use the scotch tape to plot the circles they are given on the H-R diagram based on the stars in the table. When they are done plotting, I ask them to discuss with their groups to see if they can spot any trends in their diagrams. I ask for volunteers to share the trends that they find with the class.

In the two times that I’ve done this activity, I actually observed some enthusiasm regarding these trends, as my students discovered them for themselves! We then commenced a discussion of luminosity, surface temperature, size, main-sequence mass, and (briefly) evolutionary trends in the diagram. I do not discuss cluster ages until a little later in the semester, after we have gone through stellar evolution in more detail. For my next use of this activity, I intend to add a follow-up assessment that would include multiple-choice, think-pair-share questions regarding stellar characteristics on the H-R diagram.

I also adapted this activity during the COVID-19 pandemic, in which I put each student group into a Zoom breakout room and had them share a Zoom whiteboard. They worked together to recreate the blank H-R diagram plot and drew their own colored circles on the plot to represent the stars in the table.

My students have responded positively to both of these activities, and I am eager to more thoroughly assess the intended learning outcomes of the second activity, in particular, for future semesters. I hope you and your students enjoy these active-learning explorations as well!