Alright so I have a planet where the locals are about seventeenth century level of technology, meaning sailing ships and single shot black powder weapons are the standard and there is plenty of ocean to sail across.

Also, this planet has a very visible ring.

Now it is my understanding that navigation on a ringed planet would be slightly easier since it serves as a massive billboard saying “here is the equator” and you can adjust everything accordingly. But I am more curious to learn about the exact mechanics beyond, “here is my compass, that way is north, the ring is behind me so I need a minor coarse correction.” How would something like a sextant be used on a world like this?

So, how do you use Age of Sail tools to navigate on the open ocean on a ringed planet?

Edit: a lot of people keep suggesting a similar question but this is different, I am interested in the how I already know it’s possible I am interested in the how, please stop suggesting How to navigate a ringed planet at night? it doesn’t answer the question.

  • 1
    $\begingroup$ Does this answer your question? How to navigate a ringed planet at night? $\endgroup$
    – sphennings
    Dec 18, 2020 at 1:10
  • $\begingroup$ Not really, that was stuff I was already aware of, I was more interested in the tools of sailing navigation and how they would be different from 17th-century earth. $\endgroup$ Dec 18, 2020 at 1:22
  • $\begingroup$ I think that observed angle between the ring edge and horizon would be translated to latitude. $\endgroup$
    – Alexander
    Dec 18, 2020 at 1:36
  • $\begingroup$ The ring gives you your latitude. Big deal. Latitude has never been a problem, they knew how to measure it since the antiquity. And of course they would need instruments to measure angles: human eyes are not really made to tell the difference between 44° 45′ and 45° 15′ -- and the difference is twenty (nautical) miles! To put it simply: the ring does not help navigation any more than the stars already do. $\endgroup$
    – AlexP
    Dec 18, 2020 at 1:57
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    $\begingroup$ @cowlinator fyi the North Star doesn't help those of us in the southern hemisphere. We can still use a combination of stars to determine south, though. $\endgroup$ Dec 18, 2020 at 2:11

2 Answers 2


The ring would assist in navigation at least as much as the stars do. Not only do you have a metaphorical "north/south star" (which would be the apex of the ring), but both the altitude angle and the apparent thickness of the rings would tell you your latitude.

The ring would probably be visible both day and night, and even when you can't actually see the ring apex due to cloud cover or the planet's umbra, you could probably estimate the location of the apex just by filling in the gap in the arc.

In the case where you happen to have a visible feature in the ring (like maybe a shepherd moon), you could also use a calendar and clock to determine your longitude. In the rare case where that feature happens to be at the exact altitude of geo-stationary orbit, you wouldn't even need to know the date/time.

Using a sextant to measure the ring altitude angle or geo-stationary moon would give you a much more accurate measurement of your position, so using a sextant for navigation would be invaluable.


Almost exactly the same as on Earth.

All the ring really gives you is the location of the equator (it could conceivably be some other spot; the point is that it's a fixed point). Using a sextant, they can get their latitude from this. While it will be faster (and possibly more accurate) than latitude readings on earth, the technique will be substantially the same.

Also, unless the ring happens to have some very visible "landmarks", it won't be useful for calculating longitude; they'll still need quadrants, sextants, and some very good clocks.


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