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Haverford College
Departments of Physics and Astronomy
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Astronomy 205a - Introduction to Astrophysics I

Instructor: Professor Beth Willman
Office: Strawbridge Observatory, 896-1201 (office hours to be announced)


Foundations of Astrophysics (2nd edition) by Ryden and Peterson. This book will also be used in Astronomy 206. This textbook, and some other supplementary textbooks, are held on reserve in the South wall of the Astronomy library.


1 year of calculus, 1 year of college physics. See instructor if you have any questions.

Course Description:

Astronomy 205a is the first half of a two-semester sequence (Astro 205a and Astro 206b) required for astronomy and astrophysics majors. The first semester is devoted to the study of stars (~2/3) and of the planets of our solar system (~1/3). Both of these topics involve important physical concepts and so relevant topics in physics will be introduced. This is the “physics” in “astrophysics.” Together with Astro 206b (Galactic and extragalactic astronomy, and cosmology), this course will provide a broad introduction to astronomy and astrophysics and serves as a prerequisite for the study of advanced topics. Another goal of Astro 205a is to provide an introduction to observational astronomy, through the completion of three observational projects. These will require some additional instruction in the use of telescopes during the first few weeks of class (see below).

Assignments, Quizzes, and Exams:

Homework sets are due roughly every two weeks and are turned in at the beginning of class. Collaboration on most homework problems is allowed and encouraged, although some problems will be set aside for individual work. You should treat your homework assignments as if you have written work due each week in class, rather than leaving them to the last minute. The expectation for homework, and other written work, is that I can understand exactly what you’re calculating and why without looking at the question you were asked. A lot of learning takes place in the process of doing science, not in simply getting a numerical answer as quickly as possible - written work will be evaluated as such.

There will be unscheduled in-class quizzes roughly once a week. These will be graded in class. There will be two exams, a midterm and a final. These exams are not cumulative and will each be roughly the same length. ~40% homework and quizzes, ~35% exams, ~15% observing assignments, ~10% participation. 10% credit will be lost each day that any assignment is late, up to 50% off. After ten days late, an assignment will earn no credit.

Workshops and Observing Assignments:

There will be 1 hour per week of workshops held outside of class during the first few weeks of classes, both day time and night time. These workshops will cover use of the 12” telescope and the Solar telescope. I will schedule these during the first week of class based on your availability.

Three observing projects will be assigned during the term, 2 using the 12’’ telescope and one using the Solar telescope. The first project will begin the second week of class. Students will work in teams of two or three at the telescope. After being checked out on the telescope, students are allowed to sign up for independent use of the telescope as long as they are accompanied by another qualified observer. WARNING: The weather is a formidable foe. Even though the actual number of hours you spend observing will be few, you will have to be "on call" for much of the semester. You must be willing to give observing top priority on clear evenings.

I. Observing with the 12” Schmidt-Cassegrain Telescope: You will observe a variety of astronomical objects during the semester and submit a brief (one or two sentence) description of each of your observations.

II. Sun: A solar telescope will be used to measure solar limb darkening. An analysis of this data will enable you to deduce the temperature gradient at the surface of the sun (photosphere). In addition, observations of the apparent movement of sunspots will be used to determine the sun’s rotation rate.

III. Stellar Photometry: B and V band photoelectric photometry will be used to measure the light curve of a Cepheid variable. An analysis of this data will enable you to estimate the luminosity, surface temperature, and radius of the star as well as the distance to it.


Class attendance is mandatory. A significant amount of learning will take place in the classroom from the discussions and collaborative exercises that you will engage in. All of us have things to teach and to learn from each other, so we all miss out when one student is absent. That said - if you are sick, please rest instead of coming to class. An unexcused absence will result in direct deduction from your participation grade.

Tentative Course Outline:

Week of Topic Reading
Sept. 2 Radiation Spectra and Telescopes Chapters 5 & 6
Sept. 9 The Sun Chapters 5 & 7
Sept. 16 Stars Chapters 13 & 14
Sept. 23 Stars and Binary Systems Chapters 13 & 14
Sept. 30 Stellar Structure Chapters 14 & 15
Oct.  7 Stellar Structure Chapter 15
Oct.  14 Fall Break ---------------------
Oct.  21 Star Formation and Evolution Chapters 17
Oct.  28 Stellar Evolution and Degenerate Stars Chapters 17 & 18
Nov. 4 Degenerate Stars Chapter 18
Nov. 11 Solar System Chapter 8
Nov. 18 Earth and Moon Chapter 9
Nov. 25 The Planets Chapter 10
Dec. 2 Small Bodies in the Solar System Chapters 11
Dec. 9 Formation of the Solar System and Exoplanets Chapter 12