Astro Nomenclature

Last modified date

Space is flat. It’s flat in the sense that all star systems lay on an X-Y plane where Z = 0. This is highly unrealistic, but for the sort of tabletop game that WorldGen is designed to support it keeps things simple.

What follows is a quick description of how stars, planets and other things are located and named by WorldGen when it’s creating star systems. Much is borrowed from Traveller, partly because it works for a tabletop RPG and also its what inspired much of the work on this software.

So space is flat and two-dimensional (at least at the galactic scale). It is divided into sectors, each being 32 parsecs wide and 40 parsecs tall, and each parsec being a hex numbered 01..32 (X) and 01..40 (Y).

A numbering scheme of 00-31 and 00-39 would have been so much more convenient, especially for trans-sector movement, but I’m sticking with the Traveller norms. 0101 is top left, 3240 is bottom right.

Naming Sectors

Each sector can be identified by one of three ways. The first is by official name, which is guaranteed to be unique. This might be “The Islands”, “Core” or “Deep Rift”. Not all sectors have a name though – those which have been explored, surveyed and populated will do, but beyond the edges of chartered space lay countless unnamed sectors.

Core sector is 0,0, at the centre of everything (at least officially). Positive Y is towards the galactic rim (“Rimwards”), and negative Y is towards the galactic core (“Corewards”). If “Coreward” is at the top, then positive X is to the right (“Trailing”), whilst negative X is to the left (“Spinwards”).

The X,Y coordinate of a sector provides a simple way of locating it in space, as shown in the following diagram.

There is a third way though, which is also based on the coordinate, but easier to say but harder to intuitively map to a location. Sector 0,0 is numbered “Sector 1”, and the sector immediately Coreward (0,-1) of that is “Sector 2”. Other sectors are then numbered spiralling out clockwise, so +1,-1 is “Sector 3” and 0,+1 is “Sector 6”. The higher the number, the further away you are from the core of chartered space.

This feels more like SciFi shows where regions of space tend to get referred to as “Sector 12” or “Quadrant 37” in conversation.

Sectors also have sub sectors, just like in Traveller, and can either be named or identified by a letter A to P. Each sub-sector is 8 by 10 parsecs, named A..D along the coreward side, then E-H, I-L and finally M-P.

Star Systems

Individual star systems are known by their sector and XXYY coordinate, so Core 0537 or Core 1203. They will generally also have a name, which is how the system will normally be referenced. All major objects within the system will be named after the system.

The naming system assumes perfect knowledge. Unlike ‘real’ astronomical naming, where objects are numbered in order of discovery, WorldGen numbers things according to physical properties.

This is where we really begin to add to what Traveller does, since Traveller tends to only detail one world per star system.


If the system has a single star, then it is simply named for the system. The system Torex will have a star called Torex.

Multi-star systems use a Greek suffix to denote individual stars. The first star is Alpha, then Beta, Gamma etc. So if Torex was a binary system, it would consist of Torex Alpha and Torex Beta. Alpha would normally be the primary, or most massive, star.

Note that a single star system does not name its only star Alpha, it is simply named after the system without any suffix.


Planets are named for the star they orbit, and numbered in order of increasing distance from that star. So, Torex I and Torex II, or Torex Alpha I, Torex Alpha II etc. This makes it obvious where a planet is in relation to the rest of the system, and is also feels similar to conventions already used in SciFi.

In some situations, where there is a close binary with planets orbiting the centre of gravity of both stars, the planets are named after the largest star.


Moons around planets have a lower case letter, so Torex Alpha II/b would be the second moon of Torex Alpha II. ‘a’ is the closest moon to the planet, ‘b’ the second closest etc. The moon suffix is separated from the planet name with a ‘/’.

It would be possible to run out of letters if there are more than 26 moons around a planet. This is unlikely (Jupiter and Saturn have dozens of moons, but WorldGen only lists major moons), but in the off-chance it happens the 27th moon would be aa, then ab,, ba etc.

Circumstellar Belts

Objects of the Circumstellar class are named Belt A, Belt B etc, and are interspersed amongst the planets. So our own solar system would have the following naming:

  • Sol I – Mercury
  • Sol II – Venus
  • Sol III – Earth (along with Sol III/a)
  • Sol Belt A – Asteroid Belt
  • Sol IV – Mars
  • Sol V – Jupiter
  • Sol VI – Saturn
  • Sol VII – Uranus
  • Sol VIII – Neptune
  • Sol Belt B – Kuiper Belt

Belt A would be what we consider to be the asteroid belt, and Belt B would be the Kuiper belt. For belts, the letter is always a capital.

What about poor Pluto? Or Vesta or Ceres? Major planetoids of belts are giving a lowercase roman numeral suffix, naming them as i, ii, iii etc from the innermost to the outermost, separated with a hyphen.

  • Sol Belt A
  • Sol Belt A-i – Vesta
  • Sol Belt A-ii – Ceres
  • Sol Beta B-i – Pluto

This is where perfect knowledge comes in useful – we know a new world won’t suddenly be discovered so won’t have to slot one in.

Planetary Rings

Planetary rings use an /rX suffix, such as Lorbin V/r1, which would be the first ring around the 3rd planet of the Lorbin system.

This is a ring of icy fragments that surround Lorbin V. The ring is 29 thousand kilometres in width, and the majority of the fragments are less than a metre across, with a large fraction being just a few centimetres. They are mostly pure water-ice.

A description of the ring around Lorbin V.

Planetary rings don’t have planetoids like asteroid belts do – any major worlds will be considered moons of the planet the ring orbits. A complex ring system may have multiple rings, with moons in between each.

Other Objects

Currently there is no naming scheme for other object types, such as comets or minor asteroids not considered part of a belt, mostly because WorldGen doesn’t yet support them. A Small Body object can be a planet, with a full planetary designation, but that may not be suitable in all cases.

Not all objects orbit a star. Rogue planets will exist by themselves, and how I’ll name those I haven’t decided yet. They may simply get a coordinate designation. If there are multiple ones in a hex, then how they are numbered may be from the centre of the hex. Since rogue planets aren’t supported yet though, it’s not something that’s been fully decided.

Samuel Penn