Philosophy on Learning
In addition to research, I am devoted to being a learner-centered instructor. In
all of my classes, I focus on creating an active learning environment,
and I try to make use of new techniques, including peer instruction, flipped classrooms, and in-class activities.
I am incuding many of the materials I developed for my classes here for use by anyone in the astronomical teaching community. Please just if you have questions!
Astronomy 301: Introduction to AstronomyThis course is our 101-level non-science major astronomy survey course. This course covers all areas of astronomy, from Ancient Greece, to the Solar System, to distant galaxies and the Big Bang. Starting in 2017 I taught this course in a flipped manner, where students watch short lecture-style videos at home, and much of the in-class portion consists of active learning. You can see an example syllabus here. I would be glad to provide all of my lecture materials upon . The majority of in-class activities I use in this course come from the Lecture Tutorials for Introductory Astronomy book developed by the Center for Astronomy Education. I have also developed some of my own activities detailed here:
1) Astrophysical Scales: Students work in groups through three progressive activities, studying the relative “emptiness” of the space between objects in our Solar System, between stars in our Galaxy, and between galaxies in the Universe. In each activity, we set a scale that the objects in question are the size of 12 inch paper plates which I provide. Students first predict what the scaled separation should be, and then they calculate it. Students are extremely surprised to find out that on this scale, the Moon-Earth separation and the separation between the Milky Way and our nearest large galaxy was only ~20 feet, while the separation between the Sun and the nearest star was ~4000 miles! This surprise gives them an excellent intuitive sense of the scales of objects in the universe right at the beginning of the class.
2) Phases of Venus: The first few times I taught this course, I discussed in my lecture how Galileo was able to use his telescopic observations of the changing phases of Venus as strong evidence for a Sun-centered model of the Solar System. However, students often had a hard time retaining this knowledge, so I developed this activity where students first examine an Earth-centered model, and draw what the phases would be, and find that Venus should only ever appear new or crescent. They then explore a Sun-centered model, and are able to discover for themselves that only in a Sun-centered model could one expect to see all phases (new to full and back), which is exactly what Galileo saw!
3) Dark Matter: In this activity, students have three images and corresponding captions which are some of the strongest pieces of evidence we have that dark matter exists (though I do not tell them that at the outset). I use the "jigsaw expert" method, where students first start with just one of the images, and individually study it. After a few minutes, I ask them to form a group of 2-3 students all with the same image, and to discuss what they think the image is showing. After ~five minutes, we declare that the students are “experts” on their image. They then form new groups of three, each with a different image. They share their expert knowledge, and try to deduce what physical effect the images are highlighting. We discuss as a class, and often some groups are able to deduce that some sort of ``missing gravity'' must be present.
4) Photometric Redshifts: This activity involves my own research topic of galaxy evolution. In class I first discussed the technique of photometric redshifts (approximating distances with imaging rather than more time-intensive spectroscopy). This worksheet lets them try their hand at it, using real images of distant galaxies on the first page, coupled with the filter transmission curves on the second page.
Astronomy 358: Galaxies and the UniverseThis course is our upper division course focused on the Milky Way and other galaxies near and far, aimed at physics and astronomy majors. While I teach this course more traditionally (i.e, we do the lectures in class), I strive to make it as active as possible. There are few activities available for this level of class, so I have developed several of my own which I share here. You can also see a recent syllabus for this course here.
1) Distance to Andromeda: I developed this activity as a first-day tone-setter for this course, where students duplicate the measurement originally made by Edwin Hubble in the 1920’s. Students first use the same table of Cepheids with measured periods and absolute magnitudes to derive their own period-luminosity relation. Each group then has a different set of M31 Cepheids (tarball here) with measured periods and apparent magnitudes. They use their derived P-L relation to convert the periods to absolute magnitudes, which they can then use to measure the distance.
2) Stellar Populations: This activity gives students hands on knowledge of how the light from individual stars combine to create the integrated spectrum from a galaxy. Students first calculate how many stars we would expect at each mass assuming a Salpeter initial mass function. After they calculate the number, they use transparencies which have stellar spectra printed on them, and then scale the spectra vertically for each star, and roughly add them together. They then experiment around with how color can tell you the age of a galaxy by progressively removing less and less massive stars. Although this is simplified over a true population (in that we use just one model per spectral type, e.g., O5, B5, etc., and we do not consider evolved stars), this activity allows students to gain intuition for how galaxy colors depend on the stellar population age.
3) Photometric Redshifts: In a more advanced version of what I do in my introdoctory class, here I give students an envelope with several galaxies imaged in Hubble filters, and ask them to sort them by redshift. The images are real, and each group has a different set, so this leads to quite lively discussions. The sets of images and the filter curves for the filters used are available in a tarball here.
4) Lyman Alpha Emission: This activity was created in tandem with Aaron Smith (then a PhD student at UT) to allow students to understand the resonant scattering properties of Lyman-alpha photons. Students assume all photons begin at the resonant frequency, and are first asked to predict what the profile of the line will be after scattering through the gas. They then simulate the scattering of individual photons in one dimension, using game-board spinners to simulate the random spatial and spectral diffusion of single photons as they propogate through a uniform slab of hydrogen gas. The spinner images are at the bottom of page two.
We used a "core-skipping" simplification, where anytime a photons is in the line core, we move it outside the core (this saves time, else an entire class period may be taken up by following just one photon!). When a photon has a frequency outside of the line core, the scattered frequency is given by Equation 1, which includes a Gaussian random number obtained via the Gaussian spinner. After they have the new frequency, they use the tables on page 6 to obtain the frequency-dependant distance traveled by the photon during that step (these values come from complicated Monte Carlo radiative transfer simulations, so they are provided to the students -- the main point they should understand is that when the line is close to the core, the distance moved is small, and vice versa). They then use the uniform spinner to obtain a sign, to decide whether the photon travels forwards or backwards. They record the new values in the table on page 4, and repeat the process, until the photon escapes (achieves z > 1).
Before beginning, we walked through together the example on page 3, and then did a trial photon using the table on page 4. Several dozen photons are needed to see the correct double-peaked distribution, so in practice I divded the class up into several groups, and had each group simulated as many photons as they could in ~an hour (bnetween 5-10 photons per group). We then combined all the results in a hand-drawn histogram on the board, and discussed the results, in particular comparing to their initial guesses. Images and videos of this activity being done can be seen here.