I have recently learned that the polar axis of Earth moves in a complex fashion. There are both precession and nutation. I have learned that Earth's obliquity varies between 22.1 and 24.5 degrees on a 41,000-year cycle. My questions are:
What accounts for the change of obliquity in the range of 22.1 to 24.5 degrees besides nutation, which I assume is a relatively high-frequency process consisted of many terms (like a Fourier expansion series)?
Do the ecliptic or the invariant plane of the solar system rotate with respect to the distant stars, and if so, are they responsible for the variation of Earth's obliquity?
Lastly, how should we understand the period of 41,000 years. The wiki says something I found confusing.
This cycle is a combination of precession and the largest term in the motion of the ecliptic