I populated them with some of the more powerful Inevitables from 3rd edition (The ones that governed the universal law of time, and the ones that governed the universal law of "the gods are sacred", though I ignored that flavor and just casted them as governing planar boundries. Also they were created by Dragons.) Here's what they look like:
What other places are you referring to, though? The Astral Sea is the same as the Astral Plane used to be, with the exception that the more elemental of the old Outer Planes no longer reside in them. However this doesn't need to change the "orbit" of the planes, as you can consider that the "orbit" is just a metaphor for the approaching and receding influence of the plane, regardless of its actual metaphysical position.
The Elemental Chaos and the Abyss are both new to Eberron, but I actually like their new place. I believe their current 4e position was even based upon Keith Baker's conversion notes of Paizo's Savage Coast Adventure Path, where he placed the Abyss at the "bottom" of Khyber.
I always liked the idea that the deeper into Khyber you went, the less like a "normal" Underdark it was and the more alien/strange it became. Now it's cannon. The deepest tunnels and cave networks gradually give way until you're in the Elemental Chaos (which now houses the elemental planes like Fernia and Risa), and as you keep going further into the Chaos, you eventually reach the Abyss.
Essentially, "Khyber" no longer just refers to the Underdark, but also the Elemental Chaos and the Abyss, all reachable in theory by descending into the depths below Eberron.
Personally I like them to be as literal as they are, lumps of rock orbiting the sky. They might be various kinds of rock or have something special about them (great gouts cut into them, larger or smaller than normal etc etc), but they're still rock.
What's important (at least in my setting) is that they are a physical manifestation of the orrery format of Eberron's planes. For a seer or Planeswalker, knowing where the planes are is as simple as looking up to the sky. Where is Risia or Fernia today, what's Shavarath doing right now? You can look up and see where they are in correlation. The moons are also tied to the seasons and dragonmarks. In my campaign powerful eldritch device and potent Dragonmark keyed magical items can only be constructed in the month that corresponds to that mark. And since every Month is denoted by which Moon is in ascendance (brighter and more powerful) in the sky, people have another reason to chart and note the orbits of Eberron's 12 and 1 moons.
It adds a certain sense of urgency and impetus when you've only got one full month (28 days) to piece together and complete a ritual to craft something truly powerful.
Just my two cents worth.
I don't think he was talking about tying an eldritch device to a dragonmark. I think he was saying that, in his games, he ties the construction of 1) eldritch devices and 2) potent Dragonmark keyed magical items to the Moons, because each Moon has an associated plane (For interacting with eldritch devices) and an associated dragonmark (for dragonmark focus items). But there's not any actual correlation beween eldritch devices and dragonmarks.
That being said, "eldritch devices" are not all doomsday machines. The Creation Forges that House Cannith used to create the Warforged are classified as "eldritch devices", and they were all dragonmark focus items, enhancing and empowering the Mark of Making of Cannith dragonmarked heirs.
So while I don't think PJammaGod meant to imply there was a connection, by cannon there is support for the idea.
Also, while an Eldritch Device that enhances dragonmarked powers to create Earthquakes wouldn't make sense for the Mark of Detection, I'm already getting ideas about Aberrant Marks empowering such machines.
Yikes, well we know where you sunk all your psychic skill points into Avon :P .
Speaking of Aberrant marks, an odd thought occurs to me. While the Aberrant marks themselves have no traditional connecion to the moons unlike say the normal marks, there is a thought about how they could tie in thematicaly with their powers. For example an aberrant theme tied to fire or frost obviously links in with Risia and Fernia. Your element Eldritch Device for earthquakes doesn't really tie with the Mark of Detection. But mayhap it could have an eldritch connection to Zarantyr, which is often associated with unbridled and wild energy. And more importantly you'd want Vult (the moon which ties in with stability) to be waning.
Now just find someone whom might just be the reincarntion of Halas Tarkanan (btw I such a fanboy of this guy) and bammo, revenge for all those centuries of persecution.
I knew there was a reason why Earthquakes immediately made me think of Aberrant Marks.
Yes AvonRekaes, that was why the War of the Mark was started, to take out the aberrants who had immensely powerful marks like Lord Tarkanan, who could start earthquakes, and the Lady of the Plague, whose powers were never mentioned, but its pretty obvious what the general theme of her powers were.
I'm running a game in 3.5 and I was wondering what skill people think should be used to answer questions about the moons. To know what phase they're in at a given time, or where they might be in the night sky?
I can see Knowledge (arcana) given that the motions of the sky are often a big part of mystic practices.
I can see Knowledge (the planes) given that Eberrons moons have been tied to the motion of the planes in many theories about the cosmology.
I can also see Knowledge (nature) because, well, just maybe the moons are perfectly normal moons with cycles that affect the world naturally.
Connor: Yes I know about the War of the Mark and how abberant marks used to be more dangerous. I just forgot that Tarkanan's was tied to seismic activity. It's not as if his name is as helpful in indicating his power's theme as his consort's.