Get up off the plane of the ecliptic by a couple of million miles. Look back at the Sun and watch the Earth's orbit in time-lapse for a few centuries. The orbit is an ellipse tilted at 23.5 degrees from the ecliptic. Hold station with the Sun as it rotates about the galactic center.
Question: Does that tilted ellipse -- Earth's orbit -- precess? Over millions of years, does the long axis rotate with the Sun's rotation in the galaxy? Or does it stay fixed in some larger frame of reference, such as the Local Group of galaxies? Or does it exhibit some more complex and subtle motion?
Does the long axis nutate?
Does the angle of the orbit to the ecliptic change in any periodic way?
Why? What are the forces in play?