Astronomy 355 (Spring, 2012)

Order of Magnitude Problems in Astrophysics

General Information: Enrico Fermi once asked “How many piano tuners are there in Chicago?”   This is an example of a “Fermi problem”,  namely, a problem that can be solved using estimation and approximation.  Formal education in physics and astronomy is strongly skewed toward problems with exact solutions, while actual research always requires approximations and estimates, especially in the early stages of any project (these are the famous “back of the envelope calculations”).   Students are often not exposed to such approximation methods until they actually begin to undertake research, so the goal of this course will be to develop intuition and facility with such calculations.

Time and Place: The class meets every Monday at 12:10.  We will meet in the “help desk” room, 6322 Stevenson.  There will be no class on Martin Luther King Day (Jan. 16).

Instructor: Professor Robert Scherrer

Office:  6301 and 6601

Phone:  2-2828 and 3-6419


Email is normally the easiest way to reach me.

Office hours:  Mondays, 11:00 – 12:00.  However, as the Chair, I am normally here all of the time.  Feel free to stop by whenever you like, even if the door is shut.  If you need to make an appointment, contact Don Pickert.

Grades: Grades will be based on attendance and participation.  You will be allowed one unexcused absence during the semester without affecting your grade.  Please email me for excused absences (illness, school-related travel, etc.)

Organization of the course: Most weeks, we will divide into small groups.  A problem will be assigned, and each group will be asked to develop a solution.  We will then present and discuss our solutions.  We will not be consulting internet resources during the solution of the problem (although we will sometimes do this after solving a problem).  Also, calculators should not normally be necessary, since our goal will be order-of-magnitude estimates.

We will spend a small portion of the semester examining approximation methods in more elaborate calculations, e.g., how to determine what factors are relevant in a calculation and what can be ignored, and dimensional analysis.  For these cases, we will occasionally revert to a lecture format.