I was recently looking though some files on my computer and came across a useful graphic that explains the semi-arc method of primary directions. I must have downloaded this file from the internet some years ago but I don’t remember the source. If any reader recognizes it, please let me know. Here is the image:
The was another image illustrating the difference between a solar and a sidereal day, but I found the source for it at http://csep10.phys.utk.edu/astr161/lect/time/timekeeping.html
This image is from a well-done astronomy course from the University of Tennessee.