Not talking about their changing appearance due to Earth’s and Saturn’s motions – I mean their orientation, relative to distant stars. Have we detected any motion in the plane of the rings? For that matter, how big would a change have to be to have been detected?
Meeus gives formulas for the rings’ orientation over time, but they’re relative to the changing ecliptic and equinox. He doesn’t say whether the orientation changes relative to fixed stars, or whether we know if it does. Does Saturn’s axis precess like Earth’s, and its rings with it?
The rings are tightly coupled to Saturn’s axis due to the gravitational influence of the equatorial bulge (i.e., Saturn is oblate because it rotates around its axis). Saturn does precess but it takes around a million years (as compared to Earth’s 26,000 years).
The moons disturb the rings slightly but not enough to change the overall orientation.
This is the most important factor in its oblateness. Its day is only about 10 and a half hours, second fastest of all the planets. Only Jupiter has a shorter day (just under 10 hours) and it’s visibly oblate too.
Compare that to the Earth, which has the shortest day among the terrestrial planets. The Earth is somewhat oblate, but to the human eye, it looks perfectly round.
That’s the source I used for the “million” years, although their link didn’t work. This link does, though:
And specifically:
α0 is essentially the longitude (on Saturn) of the Solar System’s north. And you can see that the time factor is 0.036T, where T is in centuries. And the whole thing is in degrees. So to go all the way around takes (360 / 0.036 * 100) = 1000000 years.
Or maybe 3000000 years. Apparently the alpha-zero and delta-zero are the plain old right ascension and declination on Earth’s celestial sphere. Presumably Saturn’s axis isn’t precessing around Earth’s axis – more likely around a line perpendicular to the solar system? So the per-century precession must be a third of the per-century change in right ascension, or less.
Didn’t astronomers with NASA also point to tiny moonlets that “shepherded” the rings, creating the gaps and keeping the material in the rings from wandering and dissipating?
That’s an amazing range! And I find it hard to image the ice zipping around a huge planet in just a few hours. If someone managed to position himself directly in the fastest ring, would it feel like being sandblasted? Or are the ice bits actually far enough apart you’d barely be hit by any of them?
