The “prime meridian” is the line through the black holes at the centers of the Milky Way and Andromeda, and the “equator” is the galactic plane.
this post was submitted on 23 Sep 2024
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If they’re intergalactic explorers, why would they care about the plane of our ordinary galaxy?
Why would they choose those 2 galaxies for a meridian?
Galactic coordinates are easy. OP asked about inter galactic.
If they’re intergalactic explorers, why would they care about the plane of our ordinary galaxy?
Because it's a convenient navigational system. If everything outside your home is arbitrary, may as well keep using landmarks you're familiar with.
LOL it took almost 200 years for humans to agree to use Greenwich as the prime meridian of Earth.
What makes you think intergalactic travelers will adopt our galaxy as the point of reference?
For the same reason GMT became the standard: Somebody has to make the clocks. Space is pretty big, but if I had to bet money, I would wager that the first intergalactic travelers would start here, where the people are, and they would start with here as their point of reference.
Why would you assume humans are the first intergalactic travelers? The universe is 14 billion years old.
Because as big as space is, time is bigger. Humans have existed for only the most recent nanosecond, and we're only just figuring out how to leave this rock. We're either going to figure out intergalactic space travel, or we might just obliterate ourselves and kill all life on the planet.
Crossing paths with another intergalactic species would be like if two different people each threw a grain of sand into the air in any desert or beach on earth at some point in the last 10,000 years, and the two grains of sand collide.
If we do find intelligent life out there, it will probably be because we have developed some intergalactic broadcast signal, and whatever comes for us might share their star maps or they might just be looking for a snack. Either way, it would take them thousands of years to hear our signal and get to us.
The post says I'm the boss, so as a human I'm going to pick my own home galaxy as the reference. Alien species would have their own coordinate systems but it's not that hard to convert between them, or to specify which reference you're using. We'll already be converting between planetary/system/galactic/intergalactic coordinate systems all the time so it's not much harder to account for a few more.
?
you orient yourself based on the galaxy you're in.
if you went to a new planet and picked up a compass would you expect it to point to your home planets North? No...
We will make them, through the might of the Helldivers.
Up. North on a map is always up.
You're in a random spot somewhere in the universe. Where's "up"?
👆🏻
Over there.
Opposite from the enemy's gate.
Jump. The direction you fall is down. Up is the other way.
Within the Milky Way a polar (cylindrical) coordinate system makes more sense than Cartesian - there's an axis of rotation to define the center and 'up/down' directions. Zero degrees is arbitrary but a line from the galactic center to Sol, projected onto the galactic plane, would be an obvious choice as a sort of galactic prime meridian. 'North' and 'south' don't really map to a roughly disc shaped galaxy - you'd use distance from center, angle, and 'elevation'.
On an intergalactic scale, the center of our own galaxy is probably still the obvious choice for a center point. We could use the same axis and meridian - I don't think the rotation of our galaxy matters on any human timescale, and on the time scales where it does matter, everything is moving relative to each other so coordinates already aren't 'fixed'. I'd use a spherical coordinate system instead of cylindrical for intergalactic coordinates, since things are not roughly in a plane anymore.
If you want a fixed coordinate you'd have to include a time dimension, and as the zero point for time I propose the Unix epoch. Not because it makes any sense but because it's extremely funny to imagine computer systems in the year 10000 still relying on that legacy decision. Though special relativity makes 'point in time' rather complex as well - I don't know enough to know what you'd actually need to make that work.
Of course we already have such coordinate systems for astronomy if you want to know the 'real' answer, one of them is pretty close to what I just came up with: https://en.wikipedia.org/wiki/Astronomical_coordinate_systems
Your polar coordinate system still needs an “angle 0” which is somewhat analogous to “North”.
The sun would be the most obvious choice for such a reference point, though it'd be amusing to make it Greenwich and therefore make everyone deal with Earth's rotation and orbit if they want extremely precise calculations (though I expect there wouldn't really be a practical difference on that scale).
Somewhat but not exactly. You can only go north or south until you hit the poles, but you can travel forever at angle zero starting from the center point. I guess you could call towards the center point "North" and away from it "south", so the galactic center is the North Pole but there is no equivalent South Pole. But angle zero is more analogous to the prime meridian - it's a line that goes north-south but there are an infinite number of such lines, and we could have called any of them zero.
SagA*
It's as good a place as any other.
This.
If you're wondering why, this is the centre of our Galaxy. Of course if you're planning on intergalactic travel, you might have some issues, but before you get too worried about it, exploring the current galaxy is going to take a while.
Edit: The link to the super massive black hole at the centre of our galaxy wasn't working.
SagA* is as good as any other galactic center for intergalactic north too. There's really no reason to pick a different one.
The link worked for me
Yeah, in the unedited version of my reply, the asterisk wasn't detected as part of the URL which lands you at Sag A, not Sag A*.
Larry Niven kind of works out this naming in several of his novels. I don't remember all the specifics, and he also used a similar scheme to describe travel in ring world, but it's close enough. First, don't bother with calling it north, that is just confusing. In the reference frame of yourself or the map you're drawing in a spinning galaxy, you've got spinward (in relation to the galactic spin) and anti-spinward, in (toward galactic center) and out, and then normal (orthogonal) to those dimensions, which you could call up and down depending on your preference. I'd probably call spinward, inward, and up positive.
If you need a reference (north) for a galactic map, it's really unlikely you'll want to use anything like grid coordinates. You can use the same ideas from the local map. You'd probably want an origin at the gravity center of the galaxy and pick another object as a reference point from which to zero angular measurements around the disc. That other object could be another galaxy (if you want to measure galactic spin itself) or something distinct and obvious in our own galaxy (if you want to navigate within the galaxy). Most civilizations would probably just use a line between their home system and galactic center as their prime meridian. Up and down should be orthogonal to spin again. If you're home planet had a magnetic pole roughly pointing out of the galactic disc (like ours), you'd probably choose your "north" pole's side up.
Well, let’s just try where a compass points to in space?
I just looked on a compass (I'm in space, currently).
It's pointing north.
Then that’s settled: we’re back to a geocentric model.
I‘m in space too, btw. Wanna grab a coffee?
Oh god yes, I need another coffee. Thanks for reminding me.
The rotation axis of the Milky Way. It seems more reliable for me than to pick two astronomical objects, as their direction might change over time. Plus it makes intuitive sense considering how we did it for Earth.
Pointing at the north pole of Earth. You didn't stipulate any other spacefaring species, so it's not like there'd be competing standards.
It would point toward the galactic plane/center of the system.
Tons of space video games do this and it actually helps orient yourself really well.
I think you would pick a north depending on your place of origin. Probably from either their own planet or, more likely, their own galaxy.
But when you get to another galaxy you'd probably have to pick again. Galaxies aren't all oriented the same way but they do roughly spin at the same speed. So, just like earth, from a certain point of view everything spins around the north south axle. But that does not have to line up to your home galaxy. And even if they did, it might spin the other way around. Much like venus spins in the opposite direction of the rest of the planets in our solar system.
What I'm trying to say is that using a universal North is completely impractical for intergalactic space travel. So you'd probably use a local system. And where that's not possible, you'd probably use your point of origin for orientation.
North is the right hand rule to galactic spin.
The location of our solar system. Everything would be in relation to where our solar system is in relation to where you are.
I'd use Earth.
Easy, the sun is the bright spot and anything else is too far away to even begin to think about exploring, so the Sun is a good point of reference for early explorers. Once you journey further than our solar system, you'd need another point of reference and it would most likely be the solar system as a whole.
I would just spin a quantum gyro, and let it decide...
The Hercules Corona-Borealis Great Wall.
We could keep using Polaris or find some really far galaxy or star as the north.
North, duh
M87