Lecture: Celestial Coordinate Systems

I just watched the short video lecture Melodie posted on celestial coordinate systems. In it, I learned a new way to think of the zenith: as a vector antiparallel to the gravity force vector. This new interpretation made so much more sense than my previous understanding of the zenith as a line pointing overhead, and I was able to visualize it a lot easier. One thing that wasn't as clear was how exactly the stars' location relative to an observer changed throughout the year. A picture or diagram of a particular star from an observer's viewpoint throughout the year would have been helpful.