Why isn't Sag A* on the Prime Meridian?

Coordinates of Sol: 0 / 0 / 0

Coordinates of Sag A*: 25.21875 / -20.90625 / 25899.96875

This is weird. AFAIK, Sag A* is the exact centre of the galaxy, and the "prime meridian" should run from Sol to it, by definition. It's not unreasonable for Sag A* to have a nonzero "height" coordinate, as there's no reason to assume that Sol is exactly on the galactic plane (and indeed these coordinates imply that Sol is somewhat "up", hence a negative coordinate for Sag A*). But that first coordinate should be zero.

There's an old sci-fi trope, "Counter-Earth", a planet on the opposite side of the Sun from Earth, forever hidden behind it. It's fallen out of use as modern spaceprobes would have found it. But the principle could be scaled up to the galaxy, with a "Counter-Sol" on the far side of Sag A*. About the only clue we've been given for the possible location of Raxxla is a comment that "I suppose we'd better put it somewhere obvious", and while the galaxy is vast, there are only a limited number of "obvious" places, and the Counter-Sol position would be one. It would even be possible to construct an in-game rationale, an experimental hyperdrive which teleports a ship to the opposite side of Sag A*'s gravity well.

But because of Sag A*'s offset, the opposite side of it would have coordinates 50.4375 / -41.8125 / 51,799.9375 - which is just over 50ly east of the galactic meridian. There's no star at those coordinates, but Drooteou PW-I a36-4 is close, at 51.5625 / -40.53125 / 51800.53125.

EDSM lists this as Derthek's Folly (also known as 'Counter Point'). The description reads:

Discovered circa 3302...

Point at which an intrepid explorer reached in a venture to locate a solar system on the far side of the galaxy that is the physically located antithesis of Sol. The system discovered turned out to be an unremarkable brown dwarf system with seven dead worlds, and one moon.

Update: 3304

It is now believed that the nearby star system of Luna's Shadow is the more appropriate location of Sol's antithesis as it lays on the zero meridian and is almost exactly the same distance from Sag-A* as Sol is.

Derthek's Folly will remain on the map for historical purposes only as it was the first genuine attempt to locate Sol's antithesis back during the era of pre-engineered jump ranges and limited route-plotting capabilities. CMDR Derthek's intrepid journey here will rightly be remembered. - Erimus Kamzel.

But as far as I can see, Derthek was correct, due to the offset of Sag A*, and the displacement of the prime meridian. I have a Carrier there now, and it is a sadly uninteresting T-class dwarf orbited by iceballs, mostly with helium atmospheres. And the area has been explored. At least I made a quick billion on a slight detour to Gru Pri LZ-D d13-6 (I dropped off 5,000t of tritium to a Carrier buying at 200k/t, and then left, he might be wondering where it came from).

Still, I'll check out a few other mirror-Bubble systems while I'm out here. Presumably I'd get them by looking up their coordinates on EDSM and subtracting them from 50.4375 / -41.8125 / 51,799.9375 - so Counter-Shinrarta-Dezhra would be around -5.28125 / -59.40625 / 51,772.78125. There's no close match, but I checked out several nearby systems (nothing noteworthy found, but I was the first to scan most of them).

Smootoae QY-S d3-202 is the system described by EDSM as "Situated on the galactic prime meridian, and 1 LY above the galactic plane z-line, some 25,898 LYs from Sagittarius A* on the far side of the galaxy, this system is the physically located antithesis of Sol". However, even if we use the galactic prime meridian, this takes no account of Sol's elevation above the galactic plane. Incidentally, astronomers agree that Sol is "above" the galactic plane, but are unsure by how much (estimated between 75ly and 101ly, rather than ED's 20.9ly).

But it's likely that if Raxxla is out here somewhere, it would be the nearest Earthlike world rather than an exact match: why set up a base on a barren iceball if there's an ELW somewhere nearby? And this is likely to apply to any other "obvious" locations too (Frontier did this with Explorers Anchorage, using the nearest ELW to Sag A*). So I'll look around for ELW's (yes I know I'm unlikely to find anything of interest..). The area around "Derthek's Folly" is explored, but I'm working outwards and now finding untagged systems (no ELW's yet though). I'll leave my Carrier parked at Derthek's Folly for awhile, and I've opened up docking permissions and services in case anyone is in the neigbourhood.
 
If Raxxla is in game (I don't for one second believe it is btw), then its likely to be in the bubble, since it dates to an era when 7 LYs was the maximum jump range ships could do. That's a point that raxxla hunters always seem to forget when exploring deep space for it.

"Frontier did this with Explorers Anchorage, using the nearest ELW to Sag A*" Additionally that's not strictly true. Frontier had nothing to do where the Explorers Anchorage was going to be built, that location was chosen by the organizes of Distant Worlds 2, Erimus Kamzel (who wrote the actual CG), and Dr. Kaii. I don't think there's any info saying what raxxla actually is, and I doubt it'll be an ELW, nor something Frontier will put at a location near Sagittarius A* and especially not one on the opposite side of the galaxy to Sol. Those locations would have been unreachable prior to the new FSD tech of the early 3300's anyway.

Of course, this is assuming Frontier stay true to the lore of the 1984 Elite novella (which at this point is anyone's guess!).
 
A meridian is a line*, and you need at least two separate points to define a line.
By definition, Sol is where we start tracing the prime meridian, and the OP is obviously (and understandably) baffled by the fact that the chosen prime meridian does not use the centre of the galaxy as the other reference.

* using line loosely here, since Sol and Sag A are not on the same plane, meridian plane (perpendicular to the galactic plane) is more correct, and that line is wholly contained in such plane.
 
Well the game has its own grid overlay on the map, with Sol at 0.0.0. I don't know why it doesn't align with Sag-A*, but I don't think that offset is a clue into where a possible raxxla location will be. Its more likely a case of Frontier being a bit sloppy when creating the overlay more than anything else imo.
 
If Raxxla is in game (I don't for one second believe it is btw), then its likely to be in the bubble, since it dates to an era when 7 LYs was the maximum jump range ships could do. That's a point that raxxla hunters always seem to forget when exploring deep space for it.
That's assuming that it's not - whatever it is - either small enough to be portable, or capable of moving under its own power. Where it was when it was originally discovered may have nothing to do with where it is now.
 
...Well, I got first-discovered on quite a lot of waterworlds and a few ammonia worlds, but I did also stumble across an ELW.

But I wasn't the first to find it. And I then found the system in EDSM:
Smootoae VE-R d4-134 (Shadow Earth)


Shadow Earth is an ELW that is situated 51,819 LYs along the zero meridian line from Sol, and 25,919 LYs from Sagittarius A*. It is thought to currently be the closest Earth-Like World discovered to the physical antithesis of Sol on the far side of the galaxy.

It's still to the east of the meridian, and actually somewhat closer to Derthek's Folly than to the meridian. So actually a better match than the meridian would indicate. Coordinates are 38.96875 / -24.90625 / 51819.53125, so just under 39ly off the meridian. Distance from Derthek's Folly is 27.64ly.
 
AFAIK, Sag A* is the exact centre of the galaxy...
Unfortunately, you are mis-informed. In the real-world MIlky Way galaxy, Sag A* is not in the exact centre of the galaxy. It's several hundred lightyears away.

A galaxy is a somewhat nebulous, fuzzy object; finding its centre requires finding it's edges, and finding the edge of a galaxy is like trying to measure the diameter of an atom, a task Isaac Asimov once described as "like trying to measure the diameter of an extremely over-ripe orange using an extremely sharp pair of calipers". However, our best estimate of the galactic barycentre is that it's several hundred light-years away from Sag A.

You might ask, "but if Sag A is the thing the whole galaxy is orbiting around, shouldn't it be in the centre, like the Sun is in the centre of the solar system?". Again, this is a mis-construction based on a flawed analogy. The sun contains 99.8% of the mass of the solar system; the gravitational median point of the solar system must, therefore, be pretty close to the centre of the Sun. By comparison, although Sag A* is extremely massive at 4.1 million Suns, it's still only a tiny fraction (0.0000001%) of the estimated total mass of the entire galaxy.

If you had the magical ability to teleport Sag A* out of the galaxy entirely, the galaxy wouldn't suddenly fly apart (like the planets would if you teleported the Sun away). Apart from the thousand cubic light-years in Sag A*'s immediate vicinity, the rest of the galaxy wouldn't even notice that Sag A* was gone. It would keep happily orbiting around itself.

As such, there is no gravitational force that is keeping Sag A* in the centre; it's free to drift about wherever it pleases. And right now, it's pleased to be several hundred light-years away from the estimated centre.

So the real question is, "Why is Sag A* in the ED universe only 25 light-years away from the centre, when it should be further?"
 
Why isn't ED's Sagittarius A* on the prime meridian? Because Elite's galaxy isn't built around Sagittarius A* the system, so to speak. You can even call it Stuemeae AA-A g0: the galaxy map search will understand. I wouldn't read too much into that though. Read up a bit on how Elite generates the galaxy, and note that its structure doesn't depend on any one system, so to speak.
In my opinion, if you're looking for the R-word, I don't think you'll find any clues in the Stellar Forge.
 
In the real-world MIlky Way galaxy, Sag A* is not in the exact centre of the galaxy. It's several hundred lightyears away.
Where did you get that number from? Wiki reports Sag A* is "almost exactly at the galactic rotational center." That's subjective, and there's more error in galactic positions than people commonly think, but still.

However, the definition provided by @Ski'Thor sheds some light, if I understand it correctly. The coordinate system is heliocentric, but it does not rotate with time. Hence as the sun moves, the coordinate system translates. "Since as defined the galactic coordinate system does not rotate with time, Sgr A* is actually decreasing in longitude at the rate of galactic rotation at the sun, Ω, approximately 5.7 milliarcseconds per year (see Oort constants)."

Edit: More directly: "the galactic coordinates of Sgr A* are latitude +0° 07′ 12″ south, longitude 0° 04′ 06″" in J2000.
 
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Correct...
The galactic coordinate system was introduced in 1958.
Some years later it was discovered, that the Prime Meridian is off about 0.07°. However, the system has no been changed.
Since Elite Dangerous is very science focused / based, they adopted the today's coordination system ;)
 
Correct...
The galactic coordinate system was introduced in 1958.
Some years later it was discovered, that the Prime Meridian is off about 0.07°. However, the system has no been changed.
Since Elite Dangerous is very science focused / based, they adopted the today's coordination system ;)
Erm, no, they didn't. The galactic coordinate system is a spherical coordinate system, Elite's coordinate systems (both internal and displayed) are Cartesian coordinate systems. It has less to do with terrestrial "convenience" and more with the task of procedurally generating a galaxy.

Plus even if Frontier went with generating the galaxy in a spherical coordinate system, the displayed coordinates would have to be converted to x, y, z anyway, since looking at spherical coordinates on the galaxy map would be less intuitive for players.
 
Well, the 1958 system had an error estimate for Sag A*'s direction of +/- 0.1 deg. It was later refined to be closer to +0.07 deg.

I don't think spherical/rectangular has anything to do with it, they are both representing positions in 3-space, and if you are ignoring error bars in positions then either representation is equivalent. I also don't think the procedural generation has anything to do with it, there are a number of hand placed systems and the supermassive black hole at the near the center of the galaxy is a prime candidate for that.

I think the answer here is that the coordinate system is off because the direction estimate was off when the system was defined. As for how closely the galactic barycenter coincides with Sag A*, I haven't found any actual numbers with error estimates.
 
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