# Stellar Mapping and Coordinates [closed]

Why are the Galactic Coordinates not aligned so that the Axes go through the Long Bar Y-axis aligned to it's longer side, positive with Sol, and the X-axis align to the center of the short length with Sol being in the negative? Z should obviously be on the galactic plane where it generally is I think...

I'm curious about whether there is a reason we shouldn't align it like this? It seems to make the most sense to me where as the current system, while I understand it, to me is just to Earth-centric, especially when we have something that stands out so much on the galactic scale you could use to figure out where you are with where as Where Sol is being 0,0,0 isn't really helpful to anyone unless you're already on Earth ^.^

The other part of my question is less "real" and more of a "I would like to know if there are any problems with doing this that I am unaware of" thing...

There are 3 question areas...

1
I use a unit I call a Lida, It is 24 terameters long and roughly equivalent to a Light Day. On this map distances will be measured in Lida, more specifically, KiloLida.
1 Sector = $$20 kL^3$$
1 Block = $$200 kL^3$$
1 Grid = $$2,000 kL^3$$
1 Octant = $$20,000 kL^3$$

Each of the bigger areas contains 1000 of the next smaller unit down and can easily be referenced by 3 digits. So if I said Grid 346 that would reference the Grid in that Octant where each of those digits are xyz starting from the Galactic Center. Lower numbers are always closer, higher are always further from the Galactic Center.

Why not use parsecs and light years? They're really not practical to use. Likewise, AU are weird, and other units you either end up with very long numbers or poor conversions. Also with this unit, I find it very easy to work out distance and time in my head. The answer is 1.07% off, but that's not really an issue when you're not trying to be 100% precise.

Why use 20kL rather than 10kL or 1kL not many stars in that volume from what I looked at before so it makes sense to use that as division and it also divides up nice to the higher divisions.

2
I use another unit.

1 brut = $$1*10^{19} kg$$

The largest reason I'm using this is that scientific notation doesn't work in emergencies or common parlance so it makes sense to me to have a larger base unit when dealing with these larger scales. $$1*10^{19} kg$$, if I remember right (cuz I came up with this a few years ago and haven't used it since), comes from when the reference point numbers on the wiki for scale started getting fishy looking to me. Not a hard science thing, but seemed like a good place to have something like this.

3
This is the way I label Stars, planets, moons, etc... because it makes sense. I keep saying that, but you know, it's true ^.^

SO I - Star (or black hole)
SO II - Spheroid
Brown Dwarf (Star?)
Gaseous Spheroid - 12,000+ km radius and above (Most of its size is from gases)
Terrestrial Spheroid - 1,500 to 12,000 km radius (Has a rocky mantle)
Icey Spheroid - 200m to 1,500 km radius (Has an ice-water mantle)
SO III - Debris
Asteroid - Comprised mainly of rock
Comet - comprised mainly of ice-water

Child Star (?) - SO I that orbits a SO I
Planet - SO II that orbits a SO I
Moon - SO II that orbits a SO II
?? (currently also called a moon it seems) - SO III that orbits a SO II

SO means Stellar Object. both SO and Spheroid are kinda bad names considering nothing but stars are Stellar and stars are Spheroids, but whatever, I think it gets the point across. Though I wish I could think up something better.

Anyways, do any of these 3 things create problems that I don't know about or that could cause a problem that I possibly can't see due to being a pleb in these matters?

• Please split this up into separate questions. In particular, your first question is relatively self-contained and astronomy-related, while the others aren't really appropriate for this forum. – Peter Erwin Sep 3 '16 at 10:54
• @PeterErwin That's ridiculous. These are astronomy questions. In particular the metrics and labeling of astronomy for mapping. The application of the knowledge may not be for astronomical purposes, but the questions relate directly to astronomy. – Durakken Sep 3 '16 at 12:07
• worldbuilding.stackexchange.com may be a better place to ask about new units and naming schemes. – Mike G Sep 3 '16 at 14:27
• @MikeG I am asking astronomy people if there will be any problem using these units for astronomy rather than whatever the standard is. Why would ask a more generalized place a more specific knowledge question. That makes no sense. – Durakken Sep 3 '16 at 14:30
• Well, of course their is a problem, the problem is that you are not using the standard. Its not a major problem it just means that you'll have to convert everything before talking to other people. Your units don't change anything fundamental, they just make communication harder. If it's your story: go ahead. If you want to do astronomy, stick to m, AU, ly and parsec, which all have useful purpose. And stick to star, brown dwarf, planet, asteroid instead of SOI. – James K Sep 3 '16 at 18:51

The reason why we centre our galactic coordinates on the sun is that is where we are.

What actually is the purpose of a coordinate system‽ I'd like to be able to point to a body and say that it is at coordinates X, Y, Z (with uncertainties in each direction)

Now we know the direction of the centre of the galaxy, but we don't know it's distance with accuracy. If we were to use the location of the centre of the galaxy for the galactic coordinates we could not give accurate coordinates for any of the local stellar objects.

If we had a warp drive and could travel halfway across the galaxy before lunch then it might make sense to use a different set of coordinates. However, as things stand there is nothing wrong with being Earth centric.

I have mentioned the remainder of the question in comments.

• Is the accuracy really that bad? Any map has high levels of inaccuracy. For planets it's due to deformations caused by sphere to rectangle. With galactic maps I would think there will always be similarly high inaccuracy due to the movement of stars being a bit more rapid than we think. If the positions were static then most stars would have to be updated a minimum of every 21 years, but that's a lot easier imo than having 400 billion numbers that you have to convert to each other to communicate once we get anything interstellar. – Durakken Sep 3 '16 at 22:08

The Galactic coordinate system was established back in the 1950s, before most people had any idea there was a bar in the Galaxy. And, as James K pointed out, it's a 2D coordinate system for describing the positions of things as seen from the Earth. You can describe the positions on the sky (2D coordinates) of just about everything, so you can give them reasonably accurate Galactic coordinates; we only know the distances to a few things, so trying to come up with with 3D positions is difficult at best, and impossible for lots of things.

To make things worse, the orientation of the bar is still a bit uncertain; different studies still disagree on its position angle at the level of 5 to 10 degrees (occasionally more). So while you could argue that a bar-relative 3D coordinate system might make sense for a galaxy-spanning civilization, it's way too early to try using something like that for contemporary astronomy.

• You mean degrees along the horizontal plane of the galaxy, not above or below the plane right? – Durakken Sep 3 '16 at 21:55
• Yes. To put it another way, if you look down on the galaxy from above and call the line between the Sun and the center of the galaxy 12 o'clock, is the bar at 0:50 (25 degrees) or 1:30 (45 degrees)? There are arguments for both, though I think the balance of the evidence favors something closer to 25 degrees. – Peter Erwin Sep 4 '16 at 14:32