Ay 102
Physics of The Interstellar Medium
(Spring Term 2017)

Left: The Large Magellenic Cloud.
Middle: The Outer Milky Way.
Right: The site of star formation near Lynds 1551.

Class Logistics ...... Policies ...... Syllabus ...... Resources ...... Problem Sets

Class Logistics

Professor: Lynne Hillenbrand (lah@astro)
Graduate Teaching Assistant: Kaew Tinyanont (st@astro)

Purpose: This is the advanced undergraduate "ism" class at Caltech. Our other junior/senior level course is "stars".
Armed with the knowledge from these two courses plus your additional physics background, you are equipped for our graduate classes.

Lectures: Mondays and Wednesdays 2:30-4:00

Problem Sets: To develop your understanding of course material, roughly weekly you will be asked to do analytic work and/or plot and analyze relevant formulae and/or data using your favorite coding language.
The last assignment will be an oral presentation during the last week of classes on an ISM topic of your choosing, guided by a recent research paper.

Exams: The mid-term assessment will be an evaluation of conceptual understanding rather than problem solving ability.
The final exam will be open note, closed book, and held during finals period. It will test both problem solving and conceptual understanding.


Problem sets are a critical means of learning the material, not just "busy work." Collaboration on problem sets is permitted in the conceptual phase of completing an assigment, though students are expected to work out the final solutions themselves. Several of the problem sets will require use of computers for calculations and plotting of results.
Exams are not collaborative but handwritten notes such as class notes may be permitted.

Grading will be based on the weekly assignments (~55%), the mid-term exam (~15%), and the final exam (~30%).

If you have either constructive feedback or complaints about this course, please come see me (or send an email). I am eager to know what is working vs not working for you in our mutual quest.


Ay 102 Syllabus and reading assignments

Beyond your course reading/studying and class attendance, a quick (daily) visit to the Astronomy Picture of the Day might broaden your astronomical horizons.



It is recommended that you review the relevant chapters in Carroll & Ostlie (Ay20 text) as a refresher on the basics.
Specifically, I suggest you go over the sections on opacity and radiative transfer (Chapter 9) and the interstellar medium and star formation (Chapter 12).

Texts that are appropriate for this upper level undergraduate course are the following.
Parallel reading assignments are given on the syllabus page.

These first two books both start out well, but then both get a little heavy on the atomic, molecular, and dust spectroscopy/chemistry,
which we will not cover in the full detail they are written about.

  • S. Kwok 2007, The Physics and Chemistry of the Interstellar Medium available from the publisher here.
  • A.G.G.M. Tielens 2005, The Physics and Chemistry of the Interstellar Medium available from the publisher here.

    A somewhat broader text is

  • M.A. Dopita & R.S. Sutherland 2005, Astrophysics of the Diffuse Universe
    (make sure you look at the 2005 "corrected third printing" or at minimum the 2003 "corrected second printing" and *not* the 2003 original, which has many deceptive errors)
    A suitable version is available from the publisher here.
    The notation used and many of the slides shown in lecture will come from this book.

    The above and a few other texts are on reserve for this course.
    In the past, location has been the astrophysics library but it may be that all Caltech course reserves are now in SFL.
    Note also that there is an e-book version of the Tielens text accessible.

    Other good references at this level are, listed in order of decreasing order of relevance, digestibility, and breadth:

  • J.E. Dyson & D.A. Williams 1997, The Physics of the Interstellar Medium
  • Maciel 2013, Astrophysics of the Interstellar Medium
  • B. Draine 2010, Physics of the Interstellar and Intergalactic Medium
  • D.E. Osterbrock & G.J. Ferland 2005, Astrophysics of Gaseous Nebulae and Active Galactic Nuclei
  • L. Spitzer 1978, Physical Processes in the Interstellar Medium
  • S.W. Stahler & F. Palla 2004, The Formation of Stars
  • D.C.B. Whittet 2002, Dust in the Galactic Environment
  • F. Shu, The Physics of Astrophysics. Volume I (Radiation) and Volume II (Gas Dynamics)
  • J. Binney & M. Merrifield 1998, Galactic Astronomy
  • G.B. Rybicki & A.P. Lightman 1979, Radiative Processes in Astrophysics
  • C.H. Townes & A.L. Schawlow, Microwave Spectroscopy

    Supplemental tutorial readings

    On-Line (arranged semi-topically)

  • Atomic and Molecular Orbitals visualization
  • Spectroscopic Notation tutorial and historical development
  • Atomic Data for nebular lines
  • Scattering by Dust basics
  • Lorentz Force basics
  • Scattering lecture slides (same physics we discussed, but focussed on terrestrial atmosphere, including rainbows!)

    Class slides

    Problem Sets

    Please please please get your sets in on time. It is easiest on everyone (the professor, the TA, and - especially - your fellow students) if all homeworks are turned in by the due date/time so that they can be graded together and turned back to you with solutions in a timely manner.

    Please write next to your name on submitted work how long it took *you* to do the set.

  • ps1 due 10 April

  • ps2 due 17 April

  • ps3 due 24 April

  • ps4 due 1 May

  • midterm assessment due 8 May

  • ps5 due 16 May

  • ps6 due 23 May FIXED problem #4 which had an issue with negative exponents appearing as positive ones due to a font issue - sorry!!

  • ps7 due 30 May this is the last problem set!

    Last Revised: 25 April 2017 by LAH