Physics 3250: An Introduction to Astrophysics....Spring 2020

NGC 6302, the "Butterfly" Nebula star cluster NGC 3603 in Carina   

(Left) NGC 6302, the "Butterfly" Nebula, a bi-polar expanding death shroud of a dead star (click to enlarge - white dwarf is the very dim dot at the geometric center), our Sun's fate 7 billion years hence. (Right) A large star cluster containing recently-formed very massive stars (or rather the massive stars are most luminous and so stand out), 20,000 ly away in the constellation of Carina. Both images were obtained by the Hubble Space Telescope. Our Sun formed within a cluster, albeit likely much smaller, 4.57 billion years ago.

Instructor: Kirk Korista
Office: 2226 Everett Tower
Office phone: (269) 387-4971
email: kirk 'dot' korista 'at' wmich 'dot' edu
Physics Department Office: 1120 Everett Tower
Physics Department phone: (269) 387-4940
Western Michigan University home page is here

  • The course textbook is An Introduction to Modern Astrophysics, 2nd Edition (2007) by Bradley Carroll & Dale Ostlie. If you have purchased the Pearson publisher version (all printings prior to October 2017), a list of corrections of typos in this version can be found hereImportant!  As of October 2017, the 2nd Edition of this this book is published by Cambridge University Press. Its webpage is found here (click on 'Resources' for some neat stuff, but none of it required in this course), and *most* of the errata (typos) in the Pearson version have been corrected in the Cambridge University Press version. You are responsible for those corrections relevant to the material covered in this course, including use of the updated physical constants. The pagination for both publisher versions of the 2nd Edition are identical - so no problems there. If you have any questions about possible errors or for any reason need help, please see me!

  • The course syllabus is here .

    The University statements on student rights and responsibilities. The Office of Student Conduct.

    A tentative listing of the Chapters to be covered (pay attention to possible changes):

    Unit 1 Measuring Stars: Read the Preface; Chapter 1 (read the very brief Section 1.4; other sections are optional background material, and not tested), Chapter 2 (all; in section 2.4, I am mainly interested that you understand the results of the virial theorem, e.g., Equations 2.46 and 2.47 and their applications), Chapter 3 (to p.75, then skim 3.6 - understand for reading context what is meant by a star's apparent magnitude and absolute magnitude (pp. 60-62), and a by star's "color" based on comparing the light that passes through two filters, but don't sweat the details), together with pp.231-235, Chapter 5 (all), Chapter 6 (skim for background information - no homework and not tested); Chapter 7 (Section 7.1 - an introduction, plus Sections 7.2 and 7.3 through p.189.  HW#3 has a sample problem on Visual Binary systems discussed in Section 7.2, and an extra credit problem on Spectroscopic Binary systems discussed in Section 7.3. You will not be examined on the details pertaining to Spectroscopic Binary systems, but you ought to be familiar with the basic idea of using the Doppler effect to acquire information about the orbit speeds, their ratio, and what that ratio tells us about the two stars' masses.).

    a) A few animations illustrating the motions of two bodies under a central force:

    This is an animation showing how the Sun and Jupiter (1047x less massive; not to scale) orbit their center of mass in 11.86 years. This "pivot point" always lies nearer to the more massive object. In reality, the Sun's motion is complicated by pull of the other planets, but most of the Sun's motion is due to the pull by Jupiter -- Jupiter's is both very massive (318x the mass of Earth) and relatively near (5.2 AU) to the Sun. (If interested in the details, see this illustrative tutorial; you won't be tested on these details.) The following are additional animations illustrating orbits of two masses around the center of mass: two equal masses (circular orbit), two equal masses (elliptical orbit; note the conservation of angular momentum in action - a bit subtle in this example), different but comparable masses, different and more disparate masses, and very different masses (the last 3 of these all have circular orbits). Note that both masses in each 2-body orbit example have the same orbital period. Which is more massive? Which has a greater orbital acceleration? greater orbit speed?  The conservation of linear momentum, m1v1 = m2v2, tells us that the ratio of masses is inversely related to the ratio of the orbit speeds. The ratio of the two masses also inversely related to the ratio of their distances from the center of mass. The textbook and the lectures will cover what you need to know about the 2-body problem for this class, but further details can be found at this Wikipedia link and additional links therefrom.

    b) You might find this simulation of an eclipsing binary system (binary stars that eclipse one another from our point of view) to be interesting. I won't be examining you on the particulars of eclipsing binary systems (discussed in Section 7.3). However, the methods by which we can measure various physical properties of stars (in particular, each of the two star's masses, radii, and the ratio of their surface temperatures) found in these special binary systems are so clever that I figured you might find them to be of interest.

    Unit 2 The Physics of Stellar Spectra: UPDATED Chapter 8 (all), Chapter 9 (most; in Section 9.5, you will not be examined on any of the details pertaining to the profiles (shapes) of spectral absorption lines or on the details pertaining to the primary measure of their strengths called "Equivalent Width" (e.g., the curve of growth concept). However, the twin concepts of the effects of the quantum mechanical probability for a specific interaction between matter and a photon and the factors (mainly T) that determine the number density or column density of absorbers present should be understood. I will not examine you on concepts related to radiation emerging from the star's surface except along the local normal (theta = 0) - so we are *probably* skipping the concept of "Limb Darkening". Do read the final section called Computer Modeling of Stellar Atmospheres). Read section 11.2 to the top of p.370 of Chapter 11 (especially those subsections that are obvious applications of those sections of Chapter 9 we discussed in class or covered in HW) alongside Chapter 9.  Ask yourself this question: why does a star's spectrum appear the way it does?  The 3 key major concepts are temperature, optical depth (and its relation to photon mean free path), and the quantum interaction between light and matter.  If you're comfortable discussing these and how they determine a star's spectrum, for a given set of elemental abundances, you should do well on the exam. And don't forget the most important diagram in all of astrophysics -- the HR diagram, and its backwards horizontal axis is the stellar effective surface temperature. I guess temperature is a key concept in this unit.

    Unit 3 Stars -- how they're built and how they work Chapter 10 (all, but just skim sections "The Mixing Length Theory..." and "Polytropic Models..." - you won't be held accountable for the details of these two topics). Pay closest attention to the readings associated with what we covered in class and in your HW.  Read section 11.1 of Chapter 11 along with Chapter 10 (especially those subsections that are obvious applications of Chapter 10). You will want to review the discussion of stellar continuous opacity on pp.244-251 in Chapter 9.   I would love to get to stellar evolution (birth, life, deaths of stars), but other than introductions these topics will need to wait for a future course. If you're interested in amazing new field of helioseismology and how we use it to plumb the physical conditions of the interior of our Sun (and now in nearby stars!), this is introduced in section 5 of Chapter 14. However, you won't be examined on helioseismology. 

    Some quotable quotes about science

    Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house. -Jules Henri Poincare is not a database of unconnected factoids but a set of methods designed to describe and interpret phenomena, past or present, aimed at building a testable body of knowledge open to rejection or confirmation. -Michael Shermer (Scientific American, September 2002)

    Like all sciences, astronomy advances most rapidly when confronted with exceptions to its theories... -from An Introduction to Modern Astrophysics (Bradley Carroll & Dale Ostlie)

    Science is a way of trying not fooling yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool. -Richard P. Feynman (Physics Nobel Laureate)

    What binds us to space-time is our rest mass, which prevents us from flying at the speed of light, when time stops and space loses meaning. In a world of light there are neither points nor moments of time; beings woven from light would live "nowhere" and "nowhen"; only poetry and mathematics are capable of speaking meaningfully about such things.  -Yuri Manin, professor of Mathematics at Northwestern University

    Recommended Reading for Fun

    If you really want to blow out your mind, read this book, Patterns in the Void...Why nothing is important, by astronomer Sten Odenwald. You might also be interested in reading some of his essays.

    I also give my highest recommendation to this book by physicist Brian Greene - The Fabric of the Cosmos: Space, Time, and the Texture of Reality. And for an excellently written, if a bit dated, grand overview of what we know about the cosmos, I recommend Timothy Ferris' The Whole Shebang - A State of the Universe Report.

    An article from the popular science magazine, Scientific American, discussing several common misconceptions of the Big Bang Theory. 

    An early video by the music group "Muse" (yeah, dating myself a little) has something to say about the true nature of gravity (if you ignore the flapping hair and shirt collar). I'm not joking; and given the titles of several of their hits, such as "Starlight", "Supermassive Black Hole", and "Neutron Star Collision", among others, one of the guys must have taken a course in astrophysics....

    What do the apparent "arrow of time" and entropy have to do with the origin of the universe? Sean Carroll's From Eternity to Here - The Origin of the Universe and the Arrow of Time addresses this at an understandable level. And this... The Big Picture - On the Origins of Life, Meaning, and the Universe about covers it, eh?

    This should be required reading for all budding scientists: The Importance of Stupidity in Scientific Research .
    Finally - you're in for a treat if you read Richard P. Feynman's QED: The Strange Theory of Light and Matter.
    Course Announcements (Pay attention for updates!)

    Computer stuff...
    (With the exception of the MS-Excel spreadsheet noted in bold immediately below, the following is optional. However, you are welcome to use the FORTRAN coding to create your own codes in C/C++ or MS Excel spreadsheets.)

    This MS-Excel spreadsheet (LTE-photosphere_I-contrib.xlsx) computes the emergent specific intensity from a stellar photosphere under simple assumptions.
  • This MS-Excel spreadsheet (orbital_vr-vtheta.xlsx) computes relative values of system orbit speed v, v(radial), and v(theta) as functions of theta for a user choice in orbit eccentricity e. A plot accompanies the tabulated results, and students can use this as a template for producing scientifically useful plots.
  • This MS-Excel spreadsheet (voigt_profile.xlsx) computes an absorption line profile (Voigt function) and absorption line curve of growth. Both sets of concepts are described in Chapter 9 of the textbook. Note -- this material is no longer covered in any detail in this couse.

    Instructions for executing the following Fortran programs; these programs might be useful on some of the homework assignments.
  • Compute your own simple elliptical orbit:  fortran code
  • Compute your own radial velocity plot vs. time for a binary system:  fortran code
  • Compute your own blackbody flux spectrum, in cgs units/Angstrom:  fortran code
  • Evaluate the blackbody flux at a particular wavelength, in cgs units/Angstrom:  fortran code
  • Compute Boltzmann relative level populations N2/N1, N3/N1, N3/N2, as well as N1/N(HI), N2/N(HI), and N3/N(HI) for H-like species:  fortran code
  • Compute ionization distributions from the Saha equation: fortran codes H(-,I,II), He(I,II,III), & Ca(I,II,III)
  • Compute the n = 2 population of H and the n = 3 population in He+, relative to the total H and Helium species: fortran code
  • Compute the emergent intensity (in cgs units/Angstrom) as a function of optical depth from a toy model photosphere of a star:  fortran code
  • Compute two very simple stellar structure models:  fortran code
  • Compute your own zero age main sequence star - a realistic, yet simplified, model using all of the physics of stars introduced in this course:  fortran code
  • Text (ascii) files containing the 2000 and 2004 Standard Solar Models: mass, density, temperature, pressure, etc as functions of the radial coordinate within the Sun. These were recent state of the art stellar interior models for our Sun.
  • A tabulation of Fundamental Physical Constants
  • Instructions for executing these Fortran programs, in case you missed the link above

    Other, completely optional, computer stuff of potential interest....

    A few cosmic web sites...

  • One of the absolute coolest astronomical images, ever (IMHO).
  • My personal page on the issue of light pollution
  • The Kalamazoo Astronomical Society (local amateur astronomy club) page is here.
  • Astronomy Picture of the Day; highly recommended - a new picture every day (since 1995).
  • What's the latest cosmic discovery by the super fantastic Hubble Space Telescope?
  • See the Earth having a bad day.
  • The new sciences of astrobiology (here is a link to graduate programs, and here is a blog "Life Unbounded") and astrochemistry (see also here; and here is a graduate program)- finding life's building blocks in the cosmos -- and maybe life itself, one day.
  • An editorial from the Kalamazoo Gazette March 12, 1998, illustrating a common misunderstanding of how science works (and a poor understanding of cosmology, which they criticize). Here is my response to that editorial,Viewpoint March 25, 1998.
  • An example of how ignorance and lack of critical thinking skills can have to read it to believe it.
  • Links to discussions of science, pseudoscience, and issues regarding science and faith...
  • You may have wondered about...the meaning of color in astronomical images; and links to discussions behind the nature of light and color.
  • A really nice description of the physics of the La Grange points of orbits, including a more detailed derivation - here. This is discussed in Chapter 18 of your textbook, and while we will not cover this specific material you might find it an interesting aside concerning binary star systems (which we will cover).

  • Your Chance to view through a telescope

  • Free Public Telescopic Observing Sessions of the night sky at the Kalamazoo Nature Center (usually beginning after twilight, if skies are clear; here is a map), sponsored by the Kalamazoo Astronomical Society (KAS),whose meetings (indoors, with cool presentations) are open to the public. Yours truely is a member and has given many presentations. Here is the scheduled list of telescopic observing session events (check the calendar year) and other important information.

  • For all observing sessions: dress appropriately; events are outdoors, and there are no restroom facilities. The KAS will supply the telescopes; all you need is a pair of eyes. However, if you have binoculars or your own telescope, feel free to bring it out. KAS members will also be happy to help you use your telescope. (Note: on occasion, the KNC staffs the gate and collects a fee per auto. If they aren't there to collect, then the event is free as the KAS intends.)

    The Orion Nebula starforming region
    Image Caption: The great Nebula in Orion. UV light of newly formed massive stars heats the skin of a giant molecular cloud to ~8000K - emission lines of hydrogen and other elements color the hot skin. You are peering into a cavern at the edge of the great cloud (some 1500 light years distant), carved out by strong UV radiation and gaseous winds of the newly formed stars (heavily over-exposed near the center of the image). Still-forming stars populate the cavern within gaseous "cocoons", while still others remained buried within the molecular cloud. The "smokey" looking gas is due to visible light absorption and scattering by embedded dust grains. (credit: European Southern Observatory and Igor Chekalin)

    Contemplate the beautiful universe...

    Here below, I've collected some of the latest images from our advanced telescopes (ground and space-based), plus a few animations and some really cool computer simulations to illustrate cosmic phenomena. These are for your casual use and perusal to help your appreciation of the cosmos - nothing below is required knowledge for this course. You'll note that I also include stuff about galaxies and cosmology. Some day, I hope to offer a second course in astrophysics covering those topics. Any how...

    ``Listening'' to the story of the cosmos

  • Telescopes

  • Star birth, life, & death

  • Our star: the Sun on the outside
  • Our star: the Sun on the inside
  • The spectra of stars
  • InterStellar Medium (ISM) and the birth of stars
  • We may get as far as the bizarre deaths of stars in this course - but feel free to sample more of our universe...
  • Star death
  • Star Clusters: an astronomer's laboratory
  • Some day, we may have a second course in Astrophysics that covers galaxies and cosmology - but feel free to continue touring the universe...I'll continue to dream....

    Galaxies and Cosmosolgy

  •  The Milky Way
  • Other Galaxies in the "local" universe
  •  Interacting or Colliding Galaxies:
  • Distant Galaxies and Cosmology

  • Kirk T. Korista
    Professor of Astronomy
    updated last:  7 January 2020
    Department of Physics
    Western Michigan University
    Kalamazoo, MI 49008-5252