# Do we know how much Saturn's rings move? **URL:** \ **Category:** Factual Questions\ **Created:** [August 2, 2025, 11:47pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638 "2025-08-02T23:47:07Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [August 2, 2025, 11:47pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/1 "2025-08-02T23:47:07Z")
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? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [August 3, 2025, 12:44am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/2 "2025-08-03T00:44:15Z")
Saturn’s rotational axis is apparently changing [(slowly)](https://phys-org.cdn.ampproject.org/v/s/phys.org/news/2021-01-saturn-tilt-moons.amp?) I would expect the ring orientation to be tightly coupled with the planet’s, but I could be wrong ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 3, 2025, 12:49am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/3 "2025-08-03T00:49:40Z")
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. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [August 3, 2025, 12:58am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/4 "2025-08-03T00:58:04Z")
Thanks - my intuition was that a planet’s tendency to make objects orbiting it orbit in its equatorial plane would be proportional to oblateness. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 3, 2025, 7:46pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/5 "2025-08-03T19:46:55Z")
And Saturn is the most oblate of the planets. Even aside from the rings, it’s oblate enough to be visible by eye in a photograph of the planet. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [August 3, 2025, 9:39pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/6 "2025-08-03T21:39:23Z")
Hey, cut the oblateness shaming! ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [August 3, 2025, 9:48pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/7 "2025-08-03T21:48:45Z")
> [@Chronos](#): > > And Saturn is the most oblate of the planets. Is that because of it’s extremely low density? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 3, 2025, 9:49pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/8 "2025-08-03T21:49:32Z")
And relatively rapid rotation. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [August 3, 2025, 10:00pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/9 "2025-08-03T22:00:33Z")
> [@Chronos](#): > > relatively rapid rotation. 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. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 3, 2025, 10:16pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/10 "2025-08-03T22:16:06Z")
You URL isn’t working and I was unsuccessful in locating a working reference. Here’s a different unofficial cite that has a bit of digested conclusions and cites some other more primary sources. > ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [August 3, 2025, 10:40pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/11 "2025-08-03T22:40:26Z")
Sorry about that - I tried to trim an excessively long URL on my phone and thought I had it right. Hope this one works > **[Saturn's tilt caused by its moons](https://phys.org/news/2021-01-saturn-tilt-moons.html)** > > Two scientists from CNRS and Sorbonne University working at the Institute of Celestial Mechanics and Ephemeris Calculation (Paris Observatory—PSL/CNRS) have just shown that the influence of Saturn's satellites can explain the tilt of the rotation... ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 3, 2025, 10:51pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/12 "2025-08-03T22:51:26Z")
Works great. Thanks. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 3, 2025, 10:55pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/13 "2025-08-03T22:55:06Z")
That’s the source I used for the “million” years, although their link didn’t work. This link does, though: > **[WGCCRE2015reprint.pdf](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/atoms/files/WGCCRE2015reprint.pdf)** > > 710.87 KB And specifically: [![Imgur](https://i.imgur.com/Wrq8LcJ.png "imgur.com") ](https://imgur.com/Wrq8LcJ) 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. ---
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [August 5, 2025, 8:34pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/14 "2025-08-05T20:34:38Z")
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. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 5, 2025, 9:15pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/15 "2025-08-05T21:15:07Z")
Good point. Probably more like \sqrt{(0.036 \cdot \cos{83.5})^2 +0.004^2} \approx 0.00571 \frac{deg}{century}. So 6.3M years. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [August 7, 2025, 1:21am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/16 "2025-08-07T01:21:46Z")
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? ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [August 7, 2025, 4:37am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/17 "2025-08-07T04:37:29Z")
Yes. > **[Shepherd moon](https://en.wikipedia.org/wiki/Shepherd_moon)** > > A shepherd moon is a small natural satellite that clears a gap in planetary ring material or keeps particles within a ring contained. The name is a result of their limiting the "herd" of the ring particles as a shepherd. > Due to their gravitational influence, shepherd moons deflect ring particles from their original orbits due to proximity or through orbital resonances. This can carve gaps in the ring system, such as the Encke Gap maintained by Saturn's moon Pan, or lead to the confining of narro... ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [August 7, 2025, 4:43am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/18 "2025-08-07T04:43:35Z")
How about moving around Saturn? I believe the rings are mostly bits of ice? If so, how long does it take a particular ice cube to orbit the planet? ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [August 7, 2025, 10:32pm UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/19 "2025-08-07T22:32:25Z")
[Answered here](https://astronomy.stackexchange.com/questions/25405/what-are-the-periods-of-saturns-rings). Varies, according to the distance of the ring. Between 5 hours and 500 days. (I presume that’s Earth days, rather than Saturn days.) ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [August 8, 2025, 2:20am UTC](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638/20 "2025-08-08T02:20:39Z")
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? [Next page](https://boards.straightdope.com/t/do-we-know-how-much-saturns-rings-move/1021638.md?page=2)