Ay 102
Physics of The Interstellar Medium
(Spring Term 2018)

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: Lee Rosenthal (lrosenth@caltech.edu)

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: MWF / 11am - 12n / Cahill 219

Problem Sets: 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.

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 (~60%), the mid-term assessment (<5%), and the final exam (~35%).

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.


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 highly 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.
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, and in an e-book version accessible from Caltech IPs 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 and from Caltech IPs 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. Note that Ay126, the graduate version of ISM/IGM, is also being taught this quarter, so might find additional relevant course reserves in that area as well.
    In the past, the reserve location has been the astrophysics library but it may be that all Caltech course reserves are now in SFL.

    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 (by S. Kulkarni) and historical development
  • Atomic Data for nebular lines
  • Scattering by Dust basics
  • Scattering lecture slides (same physics we discussed, but focussed on terrestrial atmosphere, including rainbows!)
  • Lorentz Force basics (relevant to Synchrotron radiation)

    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 11 April

  • ps2 due 18 April

  • ps3 due 25 April

  • ps4 due 2 May

  • midterm assessment due ASAP or by 9 May in class

  • ps5 due 9 May

  • ps6 due 16 May

  • ps7 due 23 May


  • ps8 due 6 Jun

    Last Revised: 22 May 2018 by LAH