Adventures in Urban Stargazing

Over the last several years, I have achieved a major pedagogical goal of mine: teaching natural science classes. This is obviously a pretty unusual opportunity for someone with a theology PhD, which is only possible because of the distinctive methodology of the Shimer Great Books School. Our discussion-centered pedagogy makes the course materials, not the professor, the center of authority, and our generalist approach means that, at least in principle, everything we read or investigate should be accessible in some way to any curious person willing to put in a little work. Hence we not only ask all our students to take courses in every discipline — even the dreaded math and science — but we expect professors to be able to teach across disciplines. The requirement is to do two out of the Big Three (humanities, natural sciences, and social sciences), but the ideal would be to teach in all, indeed to teach every core course in our curriculum.

This approach means that our science courses are very different from a typical science course, which aims to bring students up to speed with the current understanding. We focus on classic texts and experiments that exemplify profound and decisive moments of discovery. Instead of giving our students an info dump about what scientists currently think, we want to give them an experience of how scientists formulate questions and seek their answers. Older examples are better not only because they tend to be simpler to replicate (since there is less built-up background knowledge to take into account), but also because they let us see how and why scientists get things wrong.

So far I have taught two natural sciences courses — a course on the history of chemistry called What is Matter? (the old Nat Sci 1 for Shimer fans) and a course on cosmology called The Shape of the World (a new course developed since we got to North Central, taking the cosmology and astronomy portions from IS5-6 and placing them at the beginning of the Nat Sci sequence to lay a foundation of the ancient vs. modern worldviews). I had taken the former class as a student with a more experienced professor, who also happened to be a professional chemist. It was a lot of fun to finally teach it on my own, but the cosmology course is more in my wheelhouse as a theologian, and I think I’ve had more success with it.

In both cases, my goal was to make sure they grasped a handful of very vivid, memorable points that would genuinely change the way they think about the world. In the chemistry course, the most memorable and mind-blowing fact is that there is no such thing as suction — there are just differences in air pressure. The causality is exactly the opposite of what we intuitively think. When we “suck in” air, we enlarge our lungs, which creates a zone with lower air pressure within our bodies (since the same amount of air is now occupying a larger space). Seeking equilibrium, the outside air pushes its way in. We think we’re actively “sucking” it, but we’re actually creating the conditions for it to “want” to enter our lungs. There were a lot more points (surrounding how fire works, for instance), but that was the one my students latched onto the most.

For the cosmology class, we want them to understand two very simple things. (Credit to my colleague Aron Dunlap, who offered the new cosmology course for the first two years and designed these exercises.) The first is that the height of the sun goes down over the course of the fall semester. To achieve this, we create a very simple astrolabe that allowed them to measure the angular height of the sun in the sky. Then I ask them to take at least 20 readings, at roughly the same location and time of day. Lo and behold, the number goes down, much faster than they would have thought.

The second is more complex: we want them to understand that the stars appear to rotate on a circular path in the night sky. That is, we don’t want them to just memorize that fact — we want them to see it. The way we do this is by having them do observations of the night sky, separated by at least a month. We ask them to make sketches of what they see in the sky, and to identify any constellations they see (hopefully using a paper chart rather than an app, which makes it more laborious and memorable). They really struggle with this, because basically none of them have ever looked up at the night sky in any serious way. But that’s good, because once they get their observations down on paper, it’s pretty hard-won knowledge. That sets them up for the second observation, where they will have some familiarity with the basic shape of things and will therefore immediately notice that much has changed.

When I did this exercise last year (my first time teaching the class), the students were all pretty excited about it. Many reported they had never looked at the stars before and they found the experience quite moving. (When I told Prof. Dunlap about this, he quipped: “Wait till they get a load of the moral law within them!”) Still, I felt there was room for improvement. They understood that they moved, but not really how. The circular pattern that was so foundational for ancient Western cosmologies was lost on them.

Part of the problem was that I personally had so little familiarity with the night sky. I live just south of downtown Chicago, the greatest source of light pollution for hundreds of miles around. I once took the dog out after sunset and noticed to my surprise that I could see stars in a southerly direction — but not to the north, which was toward downtown. Since moving to a new apartment with a more expansive view, I have had a lot of fun tracking the phases and movements of the moon — including this morning’s Hunter’s Moon, which I saw by sheer happenstance — but limited success tracking the stars. I can see a handful of stars out of my west-facing window, but the constellations are not as familiar and the movement is not as clear. If only I could see stars to the north!

Fast forward to a few weeks ago, when I was having truly terrible insomnia. At 1 am, I decided to go out to the living room to avoid disturbing My Esteemed Partner. Unable to sleep, I thought I would at least take advantage of being awake at the darkest part of the night to check out the stars. Looking to the west, I could indeed see more stars, though they still didn’t resolve themselves into any legible shapes. Then I tried looking north and — I saw some! In fact, I could see the Big Dipper, which let me verify that I’d found the North Star (pretty obvious from the street grid in any case). I could also see Cassiopeia’s W shape, but only if I really craned my neck.

Two hours later, still awake, I decided I might as well check in on the stars — and lo and behold, things had moved! Cassiopeia was now hidden by my ceiling, and the Big Dipper had visibly moved higher in the sky. This was the first time that I personally had tracked the movement of constellations in the sky, and I could see that, as the theory would predict, they did appear to rotate around a central axis marked by the North Star. More specifically, they appear to move 15° per hour (for 360° over a 24-hour day), and that figure made sense to me for the two-hour movement I had tracked.

Now that I knew where to look, I realized that I didn’t need to wait until the ungodly hours. On a clear night, I could see stars a couple hours after sunset. Right now, when I go to bed, Cassiopeia is clearly visible in the eastern sky, and the Big Dipper is not visible (though a star tracking app verifies that it’s above the horizon in the west. On days when I happen to wake up before sunrise — 8 hours later, hence 1/3 of the circle — I see that Cassiopeia is high in the western sky. Intuitively, it looks to me like it has moved 1/3 of the way. In fact, telling My Esteemed Partner about it, I pointed to both locations and she agreed that the angle of my arm appeared to be about 1/3 of a circle. Meanwhile, the Big Dipper is clearly visible in the western sky, at what I would characterize as a medium height. Again, based on where the app places the Big Dipper when I go to bed, this intuitively seems like 1/3 of a circle.

So I’ve seen it, at least on a nightly basis. And now that I’ve got the bug, I will presumably notice the similar changes that take place over the course of a year (when the stars also appear to rotate, albeit at a much slower pace). The key here is that I only needed two constellations: the Big Dipper and Cassiopeia. Any schoolchild knows the Big Dipper, and Cassiopeia is easy to identify once you’ve seen it. It seems more fun to know more constellations, but for this basic experience, you just need the two — more might even be distracting. Both are close enough to the North Star to be visible all year round, and they are also close enough for their movement to be vividly apparent (it’s on the other side!).

If you memorized all the constellations, you’d probably forget them over time and the experience of viewing the night sky would be one of frustration and disappointment. But once you get this, you’ll never forget it. And it’s not just some arbitrary point: when you grasp this motion, you grasp the seemingly perfect circular pattern that so fascinated the ancients — and convinced the ancient Greeks, at least, that the stars pointed to the existence of an eternal and unchanging realm beyond our everyday experience. In other words, you will have experienced a very basic fact about the structure of the world, to which great thinkers have been responding since time immemorial. Not bad, I’d say.

5 thoughts on “Adventures in Urban Stargazing

  1. Thanks for this – “no such thing as suction” was an eye-opener for me. I brought a telescope in my youth that has been underutilized and this past year I joined my local astronomy club which has taught me how to polar align my scope. Previously I would point my scope at a star and have to constantly twiddle two knobs to keep the object in view. After polar alignment, I work with the rotation of the night sky only needing to turn one knob to track the star across the night sky. This post has inspired me to purchase a simple astrolabe of my own.

  2. When you write about teaching I get jealous of your students…to be in class…and jealous of you…for teaching. I love teaching, but the great books thing pulls so hard on my heart.

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