Galactic geometry and sublight travel
Lots to think about based on No Exit, but let's start by looking at one of the minor, but scientifically important revelations. The Final Five went from the 13th colony to the 12 colonies in a sublight, relativistic (meaning near the speed of light) spacecraft, first retracing their steps to Kobol, and it took about 2,000 years.
This explains their absence from the scene for so long, but it raises a lot of questions.
Anders says the 13th colony never had FTL ships. These may have been invented on Kobol after losing contact with the 13th colony.
We now know that the path of 13th Colony -> Algae Planet -> Kobol -> Colonies is under 2,000 light years.
Since Starbuck was able to take a Cylon raider and jump Kobol -> Colonies in one jump, and this is 10 times the maximum 30 light year "red line" of the colonial FTL, this distance is in the range of 300 light years.
But we also know that there was a round trip from Kobol -> 13th Colony, since the story of the landing and early days of the 13th Colony made it into the sacred scrolls the tribes took with them from Kobol 2,000 years ago. And the 13th tribe left the Algae planet 3,000 years ago. That's a problem as it states that Algae Planet -> 13th Colony -> Kobol, at sublight speed, is well under 1,000 years, making that at most a 500 light year trip. Probably much less.
So of course this doesn't add up, unless the Final Five sublight ship is not very relativistic, and they just lived on it for many centuries. Which they can do, as they are machines. Or perhaps they just had really bad luck on the trip, and took a lot of wrong turns, so that a trip of a few hundred light years as the space crow flies took 2,000 years.
But then we add the Ionian Nebula. That's 13,000 light years from the Algae Planet. Completely impossible to visit it with sublight ships. So very odd that it is the "signpost" on the way from the Algae Planet to the 13th colony, which are only a few hundred ly apart. Very odd as a choice for a location that the Final Five will wake up. Very odd place to do the strange fleet vs. Cylons confrontation including power loss, visions and return of Starbuck.
This now requires that this "signpost" is a 13,000 ly detour, both ways! It means the fleet spent 3 months trekking out to this nebula, and then another 2 months trekking back with the Demetrius on a parallel course, also trekking back 13,000 light years. Hard to imagine this is even in the range of the Demetrius without a fuel ship.
Worse, at the end of this 13,000 ly trek back, they set a rendezvous point that happens to be near real-Earth. That's OK, Starbuck got compulsions and visions about that zone, they could pick it.
Yet they set this rendezvous point so precisely that after the 13,000 ly journey -- 430 colonial jumps -- the Demetrius and base star end up right in the middle of the fleet. That doesn't make a lot of sense.
The lack of FTL does help explain how the 13th colony could have forgotten the way back to Kobol, and Kobol could have forgotten the way to the colony. It also explains how Kobol could have forgotten the location of real Earth.
If the 12 tribes didn't have FTL, they would have taken a few hundred years for their trip. I guess that's workable. We aren't told what they know of this. If so, it makes the 12 tribes a lot smarter than we thought, developing FTL when the others could not do so.
One interesting thought: Perhaps Kobol developed FTL right around the time of the exodus and the war at the 13th colony. That could suggest the 13th colony was destroyed by an FTL fleet from Kobol with a grudge, who now had an easy way to get whatever revenge they wanted without needing to take a multi-century trip. (However in this case the Final Five would not want to rush off to Kobol to warn the 12 tribes of the dangers of keeping AIs as slaves. Since they lived on an all-Cylon planet, where does this lesson suddenly come from?)
Where is "The Colony"
Cavil refers to the fact that the others "don't know about the colony" where Ellen has "all her equipment." Where is that? We suspect it has this beach that young boy John played on, so that's not the 13th colony, though this could refer to one of the 12 colonies. But they would not have left their equipment back on the 13th colony, they had to take it with them to cut their deal with the centurions.
Most likely it's just a nearby planet.
Others suggest it's the real Earth, now deserted, and this is how they will be led there. This makes sense, but since Cavil knows where this is he would not have risked using it as his ambush site. He doesn't want to tell them about it. And that's still pretty far away, about 6 Cylon jumps.