There are some aspects of teaching that don't scale very well to many people, though to be honest I doubt that more than twenty people would sign up. Among the issues are that most people have some confusion over some issues during a class, and the instructor and assistants are available to help make things clear.

For example, I can imagine that when we do the chapter about eclipsing binaries, that there will be several people who will not understand the relationship between the formulas and the physical reality. It only requires simple algebra, but some people have difficulty with formulas. It falls to the instructors to try and understand what the point of confusion is, and find a way to explain it again that makes more sense to this particular student. The more students, the more such issues per day have to be resolved. Too many students will make life not worth living for the instructor.

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Forming opinions as we speak