As of ABEM version 0.172, the unique 'Nebula' system of vanilla SR2 is not so unique. Each nebula type has its own color and characteristics, and I felt I should explain them here. (That, and I sincerely doubt Alar would let me explain that in the patch notes - besides, this lets me use images. :D)

ABEM currently has 8 nebula types, plus an 'Empty Space' system, each of which is going to get its own section in the guide:

Type 1 Nebula
Sicutmarian Nebula
Mutara Nebula
Tachyon Nebula
Pretiosian Nebula
Radioactive Nebula
Metreon Nebula
Metaphasic Nebula

NOTE: Any references to 'normal asteroids' (or simply 'asteroids') in the below guide are not necessarily 'normal' compared to (most?) vanilla asteroids. Like Ore asteroids, they can contain 500-10000 Ore each. However, unlike Ore asteroids (if I understand that bit of the code correctly), they will also contain at least one resource.

NOTE #2: The default sight range, according to Lucas, is 1500 units. Keep that in mind when looking at the sight range reductions.

NOTE #3: ABEM 0.4.0 no longer uses the default range of 1500 units. Until 0.4.0 exits beta, keep this in mind:

- The 'seeable range' modification of 0.4.0 nebulae is equivalent to the sight range modification of pre-0.4.0 nebulae. Because of this, seeable ranges didn't matter prior to 0.4.0.

- An object's 'seeable range' is how far it can be seen from by other objects. Objects inside a nebula cannot be seen by objects outside of the nebula unless the objects outside the nebula can be seen by the ones inside. Or so it used to be. (Now, if your pre-nebula sensor range exceeds 1500 units, you will be able to see out-of-nebula objects before they can even hypothetically see you. This is because we can't set seeable or sight ranges on a case-to-case basis like that.)

NOTE #4: In ABEM 0.4.0, all sight modifiers from nebulae and Empty Space have a 'priority' of 200. This means that they multiply all other sight modifiers with priorities 0-199 by whatever number is in their multiplier.

So, let's go on with the guide, shall we?

This here is empty space. From the in-game localization:

Slight gravitational anomalies caused by subspace eddies in this sector have pulled in a variety of interesting objects into an otherwise featureless region of space.

Some interesting side-effects of the subspace anomalies are that shields are formed a bit more effectively, and the gravitational anomalies they create are attracted to massive objects. This manifests itself as a 5% boost to shield regeneration and a 25% boost to sensor range.

So, what this means is that if your ship has a base regeneration of 100 shield HP per second, it will regenerate 105 shield HP in these systems. Furthermore, if your ship's base sight range and sight modifiers in the 0-199 priority range add up to 1000 units, then these systems will increase the ship's sight range by 250 units. Let's look at the contents, though.

Empty Space spawns with 1 to 4 randomly determined anomalies (debris fields), 0 to 2 random artifacts (including, to my mild annoyance, protoplanets xD), 0 to 2 normal asteroids, and 0 to 2 random creep camps. (Which, if I'm not mistaken, tend to belong to the Thereus and Kyllaros classes. Nice loot in the latter.)

That's pretty much it, though; in most games, once you're done looking for goodies, you'll just want to stuff an Outpost in systems like that for the sake of trade routes, and forget you even found it.

The Type 1 Nebula, or 'Interstellar Gas Cloud', as the status calls it, is a fabulously unremarkable place.

Description:

A fairly unimpressive nebula. Some day it might give birth to a star, but right now it's just messing with the fleet's sensors.

There may, however, be lots of interesting objects within.

Like Empty Space, this place is the sort of place you just explore, stuff an Outpost in, and forget about. It contains 1-7 anomalies, 0-4 artifacts, 0-4 asteroids and 0-2 creep camps. It also reduces seeable range to 500 units and sensor range by 66%.

The cerulean (sort of - I was aiming for it, but whether I got close enough is anyone's guess) Sicutmarian Nebula is a haven for shieldless sublight fleets in distress. Why? The description says it all:

Nebulae like these wreak havoc upon most combat systems, making them a safe haven for ships in need of repairs.

Disables shields, cloaking, FTL and weapons systems. Does not disable Boarding Parties or any form of planet killer.

So, so much as scraping the edge of this nebula will set your shields to 0, forcing you to regenerate them again. Cloaking isn't going to work, so a stealth ship still has to escape to the edge of the nebula before becoming invisible - but why would it get into that sort of situation to begin with? FTL doesn't work, so the weapon-disabling effect won't let you sit there charging your FTL drives with impunity. It may also slow legitimate travel down if you do your hyperspace/fling navigation wrong.

If someone decides to hole in inside the Sicutmarian Nebula, your best bet is to get tons of Boarding Parties, Buster Machines, Superlasers or Graviton Condensers to flush them out. Alternatively, using Go Down Fighting or Self-Destruct Devices could cause some serious damage to non-planet objects. However, even if nobody's hiding there, there's some interesting stuff inside:

2-5 anomalies
3-7 artifacts
0-4 asteroids

This nebula reduces seeable range to 1000 units, and reduces sight range by 33%.

Not quite as interesting as in the movie, but just as hazardous, the Mutara-class nebula has a way of messing with stuff.

Of all the nebulae in the galaxy, these are the hardest to fight in. Electrical discharges and massive clouds of highly charged particles render shields completely useless, and sensors don't fare much better.

However, they also make an excellent hiding place, and sometimes you can find valuable items within, perhaps even relics of battles long over...

This pink cloud of electric mayhem disables shields in the same way a Sicutmarian Nebula does; the slightest contact forces you to charge them from scratch. However, to make matters worse, objects within can only be seen from a distance of 100 units, and your sensor range is reduced to a mere fifteenth (1/15) of its usual value, making it incredibly easy to not notice your opponent until it's too late. And end up like the Reliant.

Mutara-class nebulae contain 1-4 anomalies, 0-2 artifacts, 0-2 asteroids, and 0-2 creep camps.

This blue Tachyon Nebula makes an excellent spot for a Fling Beacon or a staging area for intergalactic hyperspace jumps.

This nebula contains an unusual amount of tachyons which can be harnessed as a substitute for FTL crystals. Sensors are somewhat impaired, though.

FTL jumps out of the nebula are free.

So, this is the first nebula that has some real, permanent gameplay value. This is the sort of place you want near your core shipyards; putting down a Gate here is a good idea.

Tachyon nebulae also contain 0-5 anomalies, 1-4 artifacts, 1-3 asteroids and 0-3 creep camps. Additionally, seeable range is reduced to 750 units, and sensor range is halved.

The light pink (I was aiming for a golden color, but missed it by a mile each time I tried, so...) Pretiosian Nebula is a very precious (pun intended, though not necessarily obvious) nebula.

The exceptional amount of gold, as well as other rare metals and moderate concentrations of Ore in this nebula give it its mild color. Mining these resources from the asteroids within could provide a massive economic bonus to the owner.

So, what does this mean? Pretiosian nebulae contain 2-5 asteroids containing either Native Gold or Rare Metals, in addition to 250-3000 units of Ore.

They also contain 2-5 anomalies, 0-3 artifacts, 0-3 normal asteroids, and 1-3 creep camps, and have a fairly low impact on sensors - seeable range within is 1000 units, and sensor range is reduced by 33%.

Sickly, greenish nebulae like this Radioactive Nebula above are a ship captain's worst nightmare. Here's why:

High quantities of radioactive materials in this nebula cause significant damage to living tissue amd drastically decrease sensor range. Control computers are also damaged, with the exception of Remnant ship computers; if not evacuated within 5 minutes, control of the object will be lost.

Shields delay control loss, but take 30 (plus 0.1% of capacity) damage per second.

Nebulae such as this contain at least one asteroid rich in Uranium, with a low concentration of Ore.

So, in a nutshell: Non-Remnant objects of any kind can't stay inside the nebula for more than 5 minutes. Sure, you can use shields, but unless you have quite a bit of regeneration on them to counteract the radiation, you'll only slow the process down - plus it only works for ships.

There is a bright side to this dreadful place, though. They contain 3-7 anomalies, 1-3 artifacts, 2-5 normal asteroids, 0-3 creep camps and 1-3 valuable Radioactive (no, the game doesn't call them that, I just made that up to differentiate it from 'normal' asteroids) asteroids. Sensor range is reduced to 20%, though, and seeable range is a mere 300 units, so it'll be a long search...

Radioactive asteroids all contain Uranium, and can also have 0-1000 Ore. That's at least one free (Labor not included :P) level 2 resource right there, if you can tow the stuff out of the nebula.

(If you lose an asteroid mine, orbital or ship in there, don't fret - you can still tow it out of the nebula and use a Boarding Party on it. Keep in mind that ships rendered inert by Radioactive nebulae don't lose their boarding defense, so you may need to work harder to get those. For anything else, your Boarding Party needs to have at least 101 Boarding Strength to retake the object.)

As of version 0.180, the newly added Ulthaar race can take control of Remnant fleets. These fleets can stay in Radioactive nebulae indefinitely, and can even be gifted to allies. Similarly, reconstructed Ixions from pickups or anomalies will also be immune to the nebula, as will the Revenant and Guardian. (Shield damage will still apply, though.)

Version 0.3.0 adds the Progenitor Control Computer to the Progenitor tech tree. In addition to being a more powerful version of the regular Control Computer, this expensive endgame component renders any ship it's on immune to the radiation much like a Remnant ship.

This reddish cloud is called a Metreon Nebula. Unfortunately, we're not skilled enough to let you perform the Riker Maneuver just yet, but here's what it does:

Exceptional concentrations of metreon gas in nebulae like this one have a highly damaging effect on starship hulls. Shields slow the process down, but unless the shield generator is a powerful one, the ship will invariably have to leave to avoid destruction.

Deals 25 (plus 0.1% of the ship's maximum hull) damage per second. Shields delay hull damage, but suffer 125 damage per second, in addition to 0.1% of shield capacity.

This is generally a place you want to avoid like the plague. You can't even put an Outpost in it (well, in the late game, you could use a ship encircled in Nanite Armor to counteract the gas damage, and shields might stop it too) so it's a major navigational hazard.

Metreon nebulae do contain useful stuff, though, as usual. 2-5 anomalies, 0-3 artifacts and 0-1 asteroids await those brave (or foolish) enough to linger within this volatile cloud of death. They also limit seeable range to 750 units, and halve your sensor range.

A healthy green cloud like this one is called a Metaphasic Nebula. A fairly safe place to be, unlike some other nebulae, and perhaps just slightly valuable for shield users:

A high concentration of metaphasic particles in this nebula increases shield regeneration rates by as much as 25%, but sensors are slightly impaired.

There are probably some interesting objects within the nebula itself, if they have not been found by other empires already.

Indeed, it's just a buffed version of the Empty Space shield regenerator. At a hypothetical base regeneration rate of 100, Metaphasic nebulae will add 25 regeneration. Enough said.

They do, however, contain 1-6 anomalies, 1-4 artifacts, 0-7 asteroids, and 0-3 creep camps, with a seeable range of 1000 units. Sensor range is reduced by 33%.

So, the Metaphasic Nebula concludes this guide. Time for the credits:

- Blind Mind Studios for making a great game, and particularly (in this case, that is) for making the nebula system. Also, the gameplay of the Type 1 Nebula.

- Star Trek Armada and Armada 2 for just about every nebula in the list, and (with the exception of Tachyon, which was a decoration in STA) most of their functionality.

- Memory Beta contributors for actually letting me know about said nebulae.

- Star Trek: Wrath of Khan for the Mutara-class nebula and its functionality.

- Alarcarr for spearheading the Alternate Balance Expansion Mod; I would probably have never managed to get myself to make all this stuff if it weren't for the encouragement of the 'teamwork' aspect of the mod's development. (In other words, I'm only good at making myself make stuff when it's for others. :D)

- GGLucas and Thy Reaper (yes, they count as 'Blind Mind Studios', but who cares? :P) for helping me get on my feet through the past five months.

- A good friend who shall remain anonymous (unless he says otherwise) for telling me this game even existed.