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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.

Jacob Badger
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    Does this answer your question? How to navigate a ringed planet at night? – sphennings Dec 18 '20 at 01:10
  • 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. – Jacob Badger Dec 18 '20 at 01:22
  • I think that observed angle between the ring edge and horizon would be translated to latitude. – Alexander Dec 18 '20 at 01:36
  • 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. – AlexP Dec 18 '20 at 01:57
  • @AlexP, Earth is lucky enough to have a North Star. Imagine if we didn't. You'd definitely have to know the exact day, then do a complex calculation based on some known moving star(s). But if you have a ring, it's easy. – cowlinator Dec 18 '20 at 02:05
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    @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. – KerrAvon2055 Dec 18 '20 at 02:11
  • @KerrAvon2055, right, hence the ring is easier. You don't require much training or math skills to navigate a ringed world. – cowlinator Dec 18 '20 at 02:12
  • @cowlinator: The North Star does not sit exactly over the North Pole; it is about 1° away in the 21st century, and it was way farther away in the antiquity. You cannot rely on it to measure latitude, or to find true north; it is not used for this purpose by mariners, and never was. (As far as the mariners in the antiquity were concerned, the North Pole was devoid of stars... Our North Star was some 10° away from the Pole around 1 CE, and some 15° away around the date of the Battle of Salamina.) – AlexP Dec 18 '20 at 02:20
  • @cowlinator: And you absolutely do not need to know the day or to make any complex calculations. Just observe the culmination of any bright star, say for example Sirius; and the sun at noon will give you true north. Pytheas of Massalia knew how to do it in the 4th century BCE... – AlexP Dec 18 '20 at 02:24
  • @AlexP, I see. The point is that a ring would not necessarily make navigation more possible, just that it would make navigation easier. – cowlinator Dec 18 '20 at 02:25
  • First clarification that is required. Is your planet's ring aroun the PLANET's rotational equator, or aligned with the planet's ORBIT, or aligned with a MOON's orbit? All three of these are possiblilties. Saturn has TWO ring systems, one around its equator, one aligned with its orbit around the Sun. – PcMan Dec 18 '20 at 12:25
  • @PcMan equator. While the planet has moons, the ring isn’t aligned to their orbits. – Jacob Badger Dec 18 '20 at 18:29

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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.

cowlinator
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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.

In Hoc Signo
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