Course: AST401

Instructor: Bahcall

S 2018

### Description of Course Goals and Curriculum

This course serves as an introduction to cosmology, which is the study of the physical structure of our Universe at the largest scales, including its origin, evolution, and eventual fate. Cosmology is one of the main branches of astrophysics and is a topic of robust research in the Astrophysics and Physics Departments. Although the course is labeled as a 400-level course, the curriculum is more like that of a survey course and is easily accessible to sophomores and even freshmen. The course is broadly split into two components. The first half of the semester covers topics in observational cosmology, such as galaxy structure and classification, methods of cosmological measurement, and galactic clusters. The second half of the semester covers topics in theoretical cosmology, such as the Friedmann Equation, the Cosmic Microwave Background, and Big Bang Nucleosynthesis. The ultimate goal of this course is to provide students with the necessary background knowledge about fundamental concepts in cosmology so that they can go on to take more advanced courses on cosmology or even conduct cosmology research in the future.### Learning From Classroom Instruction

There are 2 lectures per week, each lasting 80 minutes. Because most students in the class will never have heard about any of the topics before, it is important to attend lecture. The purpose of lecture is mainly to introduce new concepts and connect those concepts with previously taught concepts. Overall, the lectures are more conceptual than computational, with only a small amount of time spent on actual derivation of equations. Therefore, especially because you will not have seen many of the topics before, it is easy to get lost in class. That being said, however, the textbook used for this class (*Introduction to Cosmology*by Barbara Ryden) is a very good reference for clearing up concepts not fully covered or explained in lecture. Therefore, if you happen to miss lecture or not understand some concept, finding the relevant section covered in the textbook and reading it will be fairly helpful for catching up. Furthermore, Prof. Bahcall is an invaluable resource. She is extremely accessible and does not even have set office hours because her door is open pretty much any time of the day. If you have trouble understanding the lecture and the textbook does not help, Prof. Bahcall will always be there to provide help and slowly step through the concepts with you until you understand.

### Learning For and From Assignments

There are 6 problem sets given in this course, 3 before the midterm break and 3 after. They are due biweekly and usually consist of 70% computational questions about the concepts taught in the past 2 weeks, and 30% conceptual questions requiring short answer responses. The main purpose of the problem sets is to make sure you understand how to apply the more abstract, conceptual ideas learned in lecture to actual, concrete problems. This is extremely important because at the end of the day, the exams will test you on your ability to apply the theoretical concepts and facts you have learned to actual problems. Therefore, it is essential that you understand how to do every single problem on the problem sets, including understanding the lines of reasoning used and derivations of relevant equations. That being said, it is also very helpful to work in groups for the problem sets, as this will allow you to learn from others and see how your classmates approach the problems. In previous years, the class usually has formed a GroupMe chat to facilitate this. Regarding assessments, there are 2 exams in this class: an in-class midterm exam and a final exam. The key to preparing for the exams and doing well on them is to understand the problems on the psets, because the majority of the questions on the exams are based off the same concepts tested in the psets. Furthermore, past exams are not released, so you cannot study from those. The makeup of the exams is roughly 70% computational and 30% conceptual short response. In the days before the exam, you should pull out the psets that you've done and rework the problems (on your own) to make sure you know how to do them. Making a cheat sheet with relevant concepts and formulas on it is also helpful to study from. That being said, it is imperative that you don't just understand the pset problems and concepts at surface-level, because some of the questions on the exam will require you to apply your understanding of the ideas learned to novel situations that you will not have seen before. Therefore, don't be afraid to ask questions in class or in office hours to clear up anything you may not understand about a particular concept! You'll be thanking yourself later on the exam.### External Resources

Because this course has a pretty fantastic support system, with Prof. Bahcall, the textbook, and your fellow peers, I find that there are not that many external resources necessary for success in this course. However, I think that elementary explanations of many of the concepts covered can be easily found online through Google or Wikipedia, if you want to read a different take on the material presented. Overall though, your best external resource will be knowing how to utilize the resources you already have in-class. Therefore, take advantage of them - go to office hours, form a study group with peers, and stay attentive in lecture.### What Students Should Know About This Course For Purposes Of Course Selection

This course is among a set of courses that are considered core requirements for the Astrophysics major. Further, the course is cross-listed with the Physics Department and counts as a departmental for both departments. Therefore, the class is mainly made up of Astrophysics majors and several Physics majors, with a few other majors from mainly STEM fields who are taking it out of interest. One important thing to note is that even though the course is labeled as a 400-level course, it is definitely not at the level of a 400-level course; many sophomores and even freshmen take the course. It is definitely one of the more easy and straightforward STEM classes at Princeton and works great as a departmental if you are an Astrophysics or Physics major. There is not much math or physics background necessary for the course besides an understanding of basic derivatives and integral calculus, and an understanding of Newtonian mechanics. Therefore, I highly encourage Astro and Physics majors, and anyone with an interest in learning more about our Universe and its origins/eventual fate to take this course.Cosmology