This site was restructured in July 2001, so if you were referred here by another website, they probably have not updated their links. If you are a student in Prof. Strobel's class, the lecture or assignment document you are looking for may not yet be available. Quizes and exams are uploaded the morning of the due date.
Lecture slides are uploaded at some time after they are presented in the day sections.
Go to the Astronomy Notes homepage to find a index of the site. Each chapter of the online textbook has a more detailed index to help you quickly find the information you want.