AST 121: The Discovery of Galaxies

In Fall 2010 I taught, for the first time, a new astronomy course called "The Discovery of Galaxies." This is a course intended for non-science majors. The course focuses on the historical development of idea about the place of our solar system within the larger universe of stars, galaxies, etc. We begin with the two sphere model of the Ancient Greeks in which the Earth was thought to sit at the center of a spherical surface, while the stars sat on this surface and rotated around the Earth once each day. We discussed ancient theories about the Milky Way and nebulae, then made our way through history examining important arguments as we went. We looked at various methods that were used to estimate the distances to stars, how the Copernican Revolution ultimately led to the conception that the Sun was one of an infinite number of stars in an endless universe, and how the invention of the telescope revealed the nature of the Milky Way and the nebulae.

Much of this first part of the course deals with very speculative attempts to understand the universe and our place in it. The middle section of the course introduces important new techniques that made stellar astronomy much more quantitative and reliable. The advent of photography, spectroscopy, and photometry radically changed the nature of astronomy and put the study of stars and nebulae in the forefront of the field. The creation of well-equipped and well-located new observatories led to tremendous advances, especially in the US.

The final part of the class dealt with the discoveries of the 20th century. These include Shapley's Big Galaxy, Hubble's discovery of Cepheid variables in the Andromeda Nebula (now the Andromeda Galaxy), the discovery of the expansion of the universe, and the eventual triumph of Big Bang cosmology.

Throughout the course the focus is on understanding the arguments used by astronomers to reach conclusions about the nature of the universe and our place within it. In many cases these arguments are faulty, or they were based on bad data, or they include hidden assumptions that turn out to be incorrect. This is part of the way science works - we slowly sift out the errors and try to keep the good stuff. My goal is to bring the excitement of real science to my students while at the same time giving them an honest view of what science is and how it works.

In order to best show my students how scientific theories are evaluated, and how theories and data are used in conjunction to reach conclusions about nature, I have the students spend their class time working through these arguments on their own. They work in small groups to complete worksheets that guide them through important arguments. In many cases they are assisted by working with computer simulations that I have created for this purpose. Anyone interested in my curricular materials can find more here:

Scale of the Universe Page

I have also written my own textbook for this course (the result of a year-long sabbatical), but the book has not yet been published.

I was generally satisfied with how the course went. I have not taught the course twice, and also taught an honors version of the course. Students seem pretty happy with the course, although they find it challenging. The mathematical level seems appropriate for my students (we use logarithms for the stellar magnitude scale, some trig for parallax, a fair bit of basic algebra, etc), but might be a little high for less selective schools (or a bit low if the audience is mostly science majors). I'm very happy with the way I am teaching the course. The activities are, I think, the most effective way for students to learn this material. They have to work through this stuff themselves. Group dynamics aren't always great, but when the groups are working well this teaching method is very effective.

For the future I would like to develop some large scale projects for the course, thus allowing me to move away from relying on exams for evaluating the students. I already have them do extensive essay writing. It makes the class grading-intensive, but I think the students get a lot out of it.

I'm hoping to publish some of the activities in The Physics Teacher in coming years, but anyone interested need not wait for that. Just look at the materials on the web site linked above.