On Earth, the cardinal directions are straightforward. The arrow on a compass points to the nearest magnetic pole. You can then use it to travel anywhere on Earth.
In space, the idea of anything being “central” enough to be used as a “North” (since the universe has no center) or being fixated enough to not somehow pose issues is more convoluted.
If you were a pioneer of space exploration, what would your “North” be?
Cosmic background radiation provides a stable frame of reference for setting up a coordinate system. If the explorers have a main HQ base, it can be set as the origin (0,0,0). The location of an object in space can be communicated using a tuple like (10km, 30°, 30°), representing the radius (distance to the object), polar angle (angle between the positive z-axis and the line connecting the origin to the point), and azimuthal angle (angle between the positive x-axis and the line connecting the origin to the point on the xy-plane).
Alternatively, if only a general region is needed, grid coordinates can be used with any useful unit of measurement for the distance between grid lines.
You would likely start from the center of your galaxy, then pick a culturally relevant star near the outskirts, in our case Sol, and call that, well, something (Solbound?) Then work your right angles from there. You could pick other cultural stars in the other directions too.
Most galaxies are pretty flat, so you’d probably have to reference a conveniently positioned other galaxy for your up and down.
I don’t think it really makes sense to have a north as such. The only potentially exception I can think of is more of a definition of ‘up’ rather than north and pertains to hemispheres of bodies.
Earth-bound cardinals are basically 2 dimensional vectors. Not really helpful in intergalactic space.
Center of gravity of the galactic cluster/supercluster
The Emperor’s psychic beacon, of course.
The Astronomican.
The Emperor Protects.
If we’re talking intergalactic navigation, I’d use QSO J0529-4351 as north.
It has the highest chance of being visible from wherever we want to go.
I was going to suggest the Great Attractor or the Shapley Supercluster, but I think your suggestion is better. It’s more point-like and since it’s farther away (well outside of the reachable universe) it results in a more uniform set of directions over long distances.
Of course, cultural influence will be big. If these explorers are Terragen then most likely the Milky Way’s north/south direction will be pretty deeply ingrained in their coordinate systems. They might keep on using that, since it’s not like manual astrolabe-style navigation will ever be relevant at that level of technology.
We could assign it to any point within a recognizable region in the Cosmic Microwave Background, which would probably be the most universally-applicable reference available. One just needs to be able to filter out the noise from surrounding celestial bodies. The CMB does slowly change over time, but so too does the position of stars within galaxies and galaxies relative to one another.
Might be a bit simple but why not the “North Star” (Polaris)? Navigation could work via analysis of stars positions relative to eachother/positions of constellations relative to the ship. You could justify it in-universe as being a nod to how early mariners used these same stars to navigate Earth’s oceans.
Earth, obviously. Or rather, where we think we left it…
By the time intergalactic navigation is relevant we’ll have likely dismantled Earth. The vast majority of it is just sitting there generating gravity, a huge waste of its potential.
Collapse imminent in minus 3 minutes. Please vacate floor -14839.