Navigation without a fixed Northern point

[Mithril Maiden]

I don't have a map of the world yet, but this question does not require a map to answer. The world is shaped like a big disk that is concave on each side (like you took two very shallow bowls and put them together). Areas closest to the rim are coldest, areas closest to the centers of the surface are warmest. So, not exactly realistic geology. One side of the disk is Thyressa, the other Thoros. At the moment, we are not worrying about Thoros right now, only Thyressa. Navigators need to be able to get from one area of Thyressa to another area of Thyressa. The center of the surface of Thyressa is South, the rim is North, clockwise is East, and counter-clockwise is West. A compass will point to the exact center of Thyressa's surface with one side, and the other in a straight line to the rim. Because the rim wraps around the entire disk that is the world, where in the rim the compass points to is dependent on the navigator's East/West orientation. There is no fixed Northern point, only a fixed Southern point. My problem is that I have no idea what that does to navigation. If we draw latitude and longitude lines all around the disk, with latitude being drawn as circles radiating out from the center and longitude as straight lines going from one end of the rim to the center, can a navigator figure out where they are with a map and compass? I honestly have no idea. I've never had to navigate by map and compass in the real world, much less some place with different rules.

[Hai-Etlik]

With just a compass, you can't figure out latitude and longitude which is why maps intended for navigation using only a compass such as portolans don't generally have latitude and longitude graticules. Compass based navigation becomes less practical as you get closer to the pole.

Determining latitude (on a globe) requires a star chart or almanac and a tool for measuring angle like a theodolite or sextant. How that would work on your world would be complicated and would depend on how the world and various celestial bodies move relative to one another.

Determining longitude (on a globe) reliably not only requires the tools for latitude, but also a very accurate portable clock like a marine chronometer. Again, dealing with your world will be complicated and depend on details of distances and movements of celestial bodies.

[Wingshaw]

If I'm not mistaken, the scenario you describe is essentially the same as anyone standing on or near the south pole. South is a fixed point, but North is, for all intents and purposes, unfixed (i.e. all directions lead North; and, obviously, the opposite is true for the north pole). If you were then to have a map of Antarctica/South Pole, it would look like a disc with south in the centre, and north on the rim--exactly what you described. If this assessment is correct, one question you can try asking is: how do polar explorers navigate?

THW

[Mithril Maiden]

If this assessment is correct, one question you can try asking is: how do polar explorers navigate?

Thank you. That's a really good idea.


Based on conversations elsewhere, I started making up an astronomical system. This is what I decided: The sun and moon are stationary and exactly opposite of each other, Edit: Better idea. The sun is above Thyressa and is stationary, and the world tilts up and down as it spins like a top, so that any specific area of the world will be high relative to the sun as dawn breaks (meaning sun is low in the sky), low relative to the sun near noon (so sun is high in the sky), and back to higher relative to the sun as the afternoon turns into evening. So, the sun will move in an arc from East to West, but areas closer to the center of Thyressa have a noticeably smaller and shallower arc and the sun seems to be moving slower, and such areas receive much more direct sunlight. At night, the sun transforms into the moon, and the same cycle happens, though the moon changes shape through the month. Because the sun is above Thyressa, the central areas are warmer and the areas near the rim are colder. Of course, in order for that to keep the rim cold, the disk that is the world has to actually be bigger in terms of diameter than the sun/moon (Sun is spherical, moon starts as a sphere and contracts into a tiny crescent, then expands back outwards. This process can tell you the time of month accurately. The world has twelve months of thirty days long, and each season is exactly three months long.). I imagine that, given the distance, the sun is maybe half the diameter of the world. There are constellations, which do not move (though the world does, so they should appear to move across the sky). Seasons are caused by the fact that the world moves vertically up and down relative to the sun/moon throughout the year, getting colder as it gets further away, and at any given point in time the entirety of Thyressa is in the same season (The world has no orbit, and neither do the sun or moon. I'm going for a full blown fantasy planet, and the climatology and geology alone violate several scientific laws. Might as well violate some Astronomical laws, too.).

Is that any help to navigation? I'm beginning to think celestial bodies are probably the most reliable method.

[Wingshaw]

That sounds like a detailed and well-worked out solar system, there. I haven't tried working out the physics-based problems yet, so I can't say how/if it is scientifically probable, and what consequences come from it.

Regarding your question about navigation, I am a big believer in inventing something in-world to assist (and avoiding 'Magic did it! Ta-dah!'). You could, for example, use
--magnetic fields (i.e. the centre of your planet is magnetic, while the edges are not, and so compasses can be used; or vice versa);
--animal migration patterns;
--strange natural phenomena (eg. aurora borealis points towards north/rim);
--ocean currents (I imagine water would flow in a generally centrifugal pattern, with the current weakest in the south, and strongest on the rim; thus the strength of currents can help navigation);
--or something a little more outlandish (stones that change colour depending on proximity to north/south due to chemical composition; rays of light that flash across the sky, and can be explained by the peculiarities of the planet's atmosphere; gravitational 'hotspots' caused by minerals in the ground--you could conceivably use this idea to have more or less than the four cardinal directions of Earth).

Basically, the idea is to be inventive, but trying to keep things rooted in scientific plausibility. I think it is the best kind of worldbuilding.

Hope that is helpful.

THW

[Ascension]

An interesting thought experiment to say the least. Having a magnetic pole would be one part of the equation, as you have to have a starting point, and yes the constellations would be the second part. Just like old times here on earth. The function really remains the same despite the planet being inverse of what earth is - an inverted sphere would be sort of like an hourglass or, as you say, two bowls stuck together on the flat side (I think). If the magnetic pole is the center, then all compasses point south (or would that actually be north and the rim be south, I dunno, but food for thought) and combined with a sextant you should be able to find your way around. The thing I'm wondering is how you get from one side of the world to the other side... pass through the neck like sands of the hourglass? You wouldn't be able to "climb" up over the rim then climb back down the outside, although that would make for an interesting sort of Limbo-type place where everything is gray and dead. Then you'd have to climb back up the rim and descend back into the "valley" of the other hemisphere. A long trek so you'd have to pack a lot of food. Maybe that's the underwold and you could kill and eat monsters for sustenance.

[MrJokee]

I don't know what everyone wrote but this is how Earth navigation works. There are two types. Absolute and Relative. Relative is a landmark navigation and as such not very useful to you if you're looking to set up a system of navigation, not unlike the systems used on Earth.

Absolute navigation uses a grid system using Lat and Long.

Latitude are lines that trend East to West to measure North to South position. They are parallel and measured 0-90 degrees on an arc. This can be helpful to you because you could say that the center is your 90 and rim is your 0 and measure from there.

Some form of actual science your people can do is creating an analema. It's a diagram that shows the position of sun on the sky at any day of the year for specific latitude. With a diagram like that you can figure out your sub-solar point, that is the highest point the sun reaches on its journey. That highest point for Earth are the tropics of Capricorn and Cancer, and the time of the year it happens on Earth being December 21, the Winter Solstice, and June 21, the Summer Solstice. These should be otherwise helpful to you because it is something people kept track of historically to know the coming and going of seasons and such.

Anyway. Longitude is an altogether different story. On Earth, Longitude was created by measuring time between different points. Every meridian is exactly 15 degrees wide, trending North to South, measuring East to West. The way that is created is that you take a watch and you record time in point of origin at noon. Then, when you reach your location, you observe noon and record the time it shows on the watch. The difference gives you the longitude where 1 hour equals to 15 degrees.

On Earth the lines converge at the poles and their maximum spread is at the equator. This can play in your favor, you could say the center of your world is the pole, rim is the equator and create a sort of clock looking thing.

Also, not sure how you have it set up, but I hope your world is not rotating because that would mean that anything close to the rim would spin at much faster rates than the things close to the center, effectively creating a sort of artificial gravity, but thats a different story and not important.

Brief:

I think your best bet is to set up a navigation system where the center if your world is a "pole" and the rim is your "equator." Then set up some important lines to simulate latitude, using the position of the sun. Then create a clock like navigation for longitude.

Hope this helps. It's basically 2 weeks of college map use course I just explained in few sentences.

[waldronate]

I often wonder why folks set up physically implausible (or impossible) worlds and then attempt to use standard physics for things like navigation. If you can have one point of attraction for each of two (or more) types of compass, then navigation becomes a simple triangulation affair. Assume that there are two type of compass (red and blue, for example), with their respective "poles" fairly far apart on the bowl. For any pair of directional readings not on a line between the poles, there are two points on the world that match that position. More types of stations gives better results. A similar scheme could be used for things that provide a distance from a point as long as you have three or more of them and some way to measure them.

As a minor thought problem, if the world is concave as you've said, shouldn't most land be visible from most places (especially at sea)? The hot real estate for gods would then be along the rim, and I expect that their brilliantly-illuminated palaces would be the fixed points needed for navigation in a simple scheme like that described above, but without need for special compasses, just good eyesight or telescopes. Even without any obvious markers along the rim, wouldn't it be possible to see some sort of major landmark from most places (allowing for atmospheric effects, of course)?

[Deadshade]

I often wonder why folks set up physically implausible (or impossible) worlds and then attempt to use standard physics for things like navigation. If you can have one point of attraction for each of two (or more) types of compass, then navigation becomes a simple triangulation affair.)

This.
There is only one privileged direction - centerwards. Because of the rotational symmetry, every direction rimwards is equivalent. So it is impossible to navigate unless, like Waldronate said, there are visible rim landmarks or sun or stars. I any of these are available then navigating is indeed just a simple triangulation because what one needs is just a second fixed direction that breaks the rotational symmetry.