the star trails are stacked. each shot was 4 minutes with one second in between. If you take more than one second, you get a visible break in the streak of light. That explains the small breaks (i don't necessarily mind them.) Getting a proper foreground exposure, then changing all your settings in one second to get a proper background exposure for the next 20 shots is tricky, so that happens. If you're referring to the stars in general, I suppose it has to do with where the star is in relation to Polaris. The further away it is, the wider the arc it makes in rotation around the star.

about 4 or 5 hours from start to finish. it took about 8 attempts to get the foreground lighting how I wanted it because it was all done with a flashlight and colored gels.