Homework
Purpose of Homeworks (In Order of Importance)
They are an extension of instruction: they represent applications of principles covered in class to astrophysical systems.
They offer practice in solving problems. As such they constitute preparation for exams.
They earn you credit towards the final grade for the course (25% of the grade depends on the homeworks).
General Rules and Regulations
To receive credit for a homework, it must be turned in on time. There are no extensions to the homework deadline, since solutions are distributed at the deadline, nor can homeworks be made up.
While working on homeworks you can exchange ideas with your classmates (brainstorm/strategize). However, you should figure out the details and write out the solutions on your own. See also the section of the syllabus on assessed work.
In some assignments that involve writing code to analyze data and make plots you will be asked to work with a partner. For those assignments turn in only one set of solutions per team (both partners will get the same score).
Specific Instructions on Homework and Exam Solutions and Presentation
To get full credit for your solutions to homework and exam problems, you must follow the instructions below.
Always solve problems algebraically (without inserting numbers) to the maximum extent possible. Derive final formulae and insert numbers only at the very end. There are many good reasons for doing so:
It is very instructive and it allows you you to see how different physical effects come into play in the problem (this is a major goal of this course).
It reduces number crunching (which is more prone to error and more difficult to check).
It increases the probability of earning partial credit, if you do not solve the problem correctly, because it makes the method easier to follow.
Carry the units around in all your numerical calculations. They provide a sanity check and can help you spot mistakes. And do not forget to attach units on your final answers. Use appropriate and sensible units in your answers. For example, express long time scales in years instead of seconds and large masses in solar masses instead of grams.
Always present the solutions to integrals and differential equations that you encounter. If you do not know how to solve them, you can look up the solution and reproduce it; do not just quote an answer. The only exception are integrals that are discussed and solved in class and/or whose solutions are included in the formula sheet or in the problem itself.
Use the data (physical and astronomical constants) from the data sheets in the course packet. These are in the units and conventions followed in this course. They are also at the appropriate precision.
Whenever you draw information from the course packet, give a precise citation, including figure or table number and page. For example, do not say "according to the course packet, the core of this star is convective;" instead say "according to figure 36 on page 29 of the course packet , the core of this star is convective."
Your solutions should be complete, clear, well organized, and neat:
Write neatly and spread out the text and equations.
Write text to explain your logic and the steps of the calculation.
Show all the details of your work. Do not skip any steps.
Use proper, conventional scientific notation.
You are likely to loose points if your solutions are difficult to understand, if they are missing essential elements or steps, if they do not follow the instructions given (in the syllabus and problem), or if the answers are not expressed in the appropriate form, format, or convention. It always pays to read the problem carefully and follow the instructions therein.
Some Advice
Start working on assignments early! Some of the problems require a lot of thought and/or consultation with the instructor (by design). Be ready to come to office hours with your questions. If you wait until the day before the assignment is due you will not have enough time to do a good job and you may miss the chance to go to office hours.
Study the lecture material carefully before attempting the problems. Attempting the homework problems "cold" is inefficient and defeats the purpose of the homeworks.
Read questions carefully and understand what you are asked to do. Then, answer the questions completely (do not leave parts out).
Think critically about the answers you get at every step and ask yourselves if they make sense. This is a very important part of the exercise because (a) it helps you catch mistakes that are sometimes subtle and (b) it makes you take a step back and look at the solution critically and test your general understanding of what is going on.
When carrying out numerical calculations keep at least 4 significant figures until you get a final answer. This improves the accuracy of your calculation and protects from round-off errors and other numerical traps. Truncate the number at the end so that you do not give a false sense of precision.
In the same spirit as above, do not convert decimals into fractions because it misleads the reader about the precision. For example, if you get a numerical answer that is very close to 3.5, do not write it as 7/2. This is particularly important for exponents.
It is extremely useful to do the problems, even if you miss the deadline because of reasons listed in the first section of this handout.
When you get the official solutions for the homeworks, study them carefully even if you got the answer right. They may show you a different way of approaching the problem that what you came up with and they may add to your understanding of the physical system that is the topic of the problem.