Ionian Nebula
The Ionian nebula is approximately 13,000 light years distant from the algae planet. It encompasses a star system with at least two planets.
In their search for the Eye of Jupiter's function and symbolism, Lieutenant Felix Gaeta discovers that a nova occurred in the Ionian system which was seen 4,000 years ago, around the time the 13th tribe left Kobol. The nova left behind a gas cloud, known to the Colonials as the Ionian nebula (Rapture).
As Gaius Baltar's trial starts, the Fleet has almost reached the nebula and hopes to find its next clue to the location of Earth (Crossroads, Part I). When Baltar is acquitted of his crimes on New Caprica, Admiral Adama and the four other captains are released from their duty as judges and are free to finally make the jump to the nebula. When the fleet jumps into the nebula it is stricken with an abrupt power outage, every ship in the fleet looses power all at once. As the ships drift dead in space and without DRADIS four Cylon Basestars also jump into the nebula and begin launching Raiders. When power is finally restored to Galactica they discover the Basestars, however the fleet, having had to completely restart all their systems, is unable to jump away in time. Galatica launches all it's Vipers and Raptors to intercept the Raiders and Admiral Adama authorizes the use of nuclear weapons against the Baseships.
During the battle, Lee Adama picks up an "Unknown" contact on DRADIS and breaks off to intercept it. The unknown bogey leads him on a chase through the dust clouds of the nebula and after outmaneuvering Adama's Viper pulls up along side him. Much to Lee's surprise the "Unknown" contact is actually the supposedly dead Captain Kara "Starbuck" Thrace" piloting an unusually pristine Viper Mk. II. Thrace claims to have been to Earth and that she is going to lead the fleet there. The outcome of the battle however, is yet to be determined (Crossroads, Part II).