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My question arises from how to treat navigation within an unknown star system, based on what is in that star system. System North and South can be easy to determine - just observe the directions in which the planets rotate, and use convention - our own solar system - as a guide.

But how do you determine the zero point in terms of rotational/angular distance along the plane of the solar system? My first thought was to use the core of the galaxy as the “zero degree mark”, but some solar systems can have either their North or South “poles” pointing directly at the galactic core. You can’t always assume a solar system will be somewhat edge-facing the galactic core. So without a workaround for edge cases (har, har), this wouldn’t be appropriate in 100% of all cases.

And unlike our own solar system, the constellations would be somewhat to radically different in this new solar system, so you would be unable to use the constellations as a positioning system for where the planets and other ships are currently located.

So I am curious if there is a sol-independent, constellation-independent way of GPS-ing an entire solar system just based off of what it is in it. I am looking for a way that any sentient visiting a brand-new system could quickly set up a way of referencing distances and positions within that solar system in ways that anyone else using the same set of system-independent rules can come to the same determination without having to communicate with each other ahead of time.

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  • $\begingroup$ Hello, René, welcome to Worldbuilding. When you have a moment, please take our tour and read through the first two bullets of our help center to better understand the site. Can you clarify what you're asking? Planetary distances suggests you're only trying to map the solar system (polar coordinates with the star as the zero point). But you talk like you're trying to map the solar system in terms of its placement in the galaxy, which is a much, much more complex question (and might have a duplicate on the site already). $\endgroup$
    – JBH
    Dec 10, 2020 at 4:19
  • $\begingroup$ Polar coordinates with the star at its zero point is one solution, but only a partial one. Because without some sort of reference from outside the system, how can two independent visitors achieve the same reference system without communicating? There has to be some way of figuring out a “angle zero” against which other objects in the solar system can be measured against the plane of the system. $\endgroup$
    – René Kåbis
    Dec 10, 2020 at 4:26
  • $\begingroup$ Ah... I see your point. How do you define "zero degrees" around the rotational axis of the sun? If you think about it, it doesn't matter if the two visitors don't have the same zero-point because it's trivial math to work it out based on where all the planets are at a specified time. Ship A, "We declare the line through planet #6 to be zero at T=+25s." Ship B, "OK..." Everybody knows where all the planets are (well... theoretically). $\endgroup$
    – JBH
    Dec 10, 2020 at 17:58

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Remember that stars rotate too. Assume that the star's axis determines the 0⁰ orbital plane, then work your way around that. Once you've determined the plane, longitude 0 is the closest one to the core if the star is tilted up to some arbitrary angle relative to the galaxy. Above that angle, use another well known galaxy as reference instead.

That is precise even if a star has no planets, or if for whatever reason they are not mostly neatly in a narrow range of angles such as our own system.

If you have more than one star in the system, either use the most massive one, or set a base plane from the median of their rotation planes.

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Set up relative to the galactic barycentre.

Why? In order to synchronise universal time, you need to convert solar system coordinate time to galaxy coordinate time - that requires calculating exact orbits of the sun around the galaxy centre in order to correct for relativity.

Since you are going to the trouble of syncing your clocks to the correct local time zone anyway, and that requires calculating the orbit exactly, you might as well inherit the orientation of the galaxy barycentre while you're doing this maths.

Solar system may have multiple planes, or none, they may have no planets. They may have counter rotation or multiple suns. No rule will work for all, so just inherit the galactic standard as your base orientation.

That galactic standard may be arbitrary, but at least its consistent.

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And unlike our own solar system, the constellations would be somewhat to radically different in this new solar system, so you would be unable to use the constellations as a positioning system for where the planets and other ships are currently located.

Distant stars are going to be arranged differently, and instead of the big dipper one might have the not so big dumpling steamer, but they won't move, so they can act as point of reference for your movements. Just pick an association of stars which stands out and use it as reference for the 0 together with the central star.

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    $\begingroup$ How can this be determined identically between two system visitors without communicating? Galactic core is one universal metric that can be used in any star system in any galaxy to determine a “zero degree start point” along the orbital plane, but the system's poles could be pointing directly at the galactic core, preventing any angle-in-plane of measurement from being determined.. $\endgroup$
    – René Kåbis
    Dec 10, 2020 at 4:29
  • $\begingroup$ @RenéKåbis, reference frames are a matter of convention. If you don't communicate the convention you won't agree on it. $\endgroup$
    – L.Dutch ♦
    Dec 10, 2020 at 4:32
  • $\begingroup$ But convention can exist regardless of the solar system. Two visitors need not to have ever spoken to each other before and yet still have the shared convention to agree on that system of navigation without needing to hash it out beforehand. THAT is what I am looking for - a convention that will work regardless of the solar system, or what other stars are in its sky. I am looking for the common elements that will allow me to determine an “angle zero” regardless of the solar system I am in, and to have others that work from the same convention come up with the same measurements automatically. $\endgroup$
    – René Kåbis
    Dec 10, 2020 at 4:36
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"Based on what is in the star system":

Pick a center (e.g. the sun) and a plane of reference (e.g. a planet's orbital plane) as ecliptic, choose north and south as you see fit and a few reference stars whose positions are known. Sun's center and planet's orbit can be observed while "dropping in", if the spaceship dropping in has an own navigational reference. But they got there, so they do, and they have some stars for reference they can simply keep using. Then do a little trigonometry, divide the plane and a circle perpendicular into parts (360, because it is divisible by oh so many divisors), that is how we too navigate since centuries and it works anywhere, in any solar system, and only needs exact time and a measuring equipment for angles to determine a position.

Multi-star systems are more complicated, but can be handled as well, depending on the setting and stability.

https://en.wikipedia.org/wiki/Celestial_coordinate_system

GPS is completely arbitrary and has no meaning in a solar system. Its coordinates are based on a reference ellipsoid for a given planet, not for a solar system. GPS coordinates are tranformed back and forth between cartesian (which is good for computers) and anything human readable or whatever fits a given use case. They can build an own GPS once they have a grasp of the globe and a herd of satellites around it.

A (proposed) navigation method for deep space are pulsars, galactic "light houses" with a fixed "signal" (just like our light houses !). I leave this link here for reference:

https://www.nasa.gov/mission_pages/station/research/news/future-space-travelers-may-follow-cosmic-lighthouses-sextant-results

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A discussion that came up in another forum may be of use to you.

The use of directionals in a space-faring race. This essentially describes a universal stacked system of direction defining based upon the behaviour of the relevant body (a planet, a star system, an astral system / galaxy).

This system will instantly give your spacefarers the basic "gridwork" upon which to establish the various local reference points. All they have to do is plug in the values for each planet such as it's location, orbital east direction and velocity become more known than they already were.

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