International Space Station Recently, I have been going out to observe the ISS when it is within sight of my location.  I have noticed that the ISS, based on the time that I have to observe the space station during any given transit, moves at a fairly constant speed across the sky, depending on the degree of elevation and maybe some other factors related to the seeing conditions.

My question relates to the different course the space station takes when traversing over my location. There may be as long as several weeks when the ISS is not within viewing parameters for my location. Why does the course across the sky vary from time to time?
I recommend you to take a look at Wikipedia about the ISS's orbit: Wikiepdia - ISS: Orbit

There is also a very interesting video that I think will answer to your question: ISS Orbit animation