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 purpose and symbolism, Lieutenant Felix Gaeta discovers that a nova occurred in the Ionian system which would have been observed 4,000 years ago on ancient Kobol, around the time of the Thirteenth Tribe's exodus. The timing of the nova with the Thirteenth Tribe's journey and its resemblance to the algae planet system's nova suggests to Gaeta that the Tribe's next marker is the Ionian Nebula (Rapture). Galactica and her Fleet begin the journey to this next waypoint to Earth.

As Gaius Baltar's trial begins, the Fleet has almost reached the nebula, despite some fuel processing problems and labor unrest, and the loss of pilot Kara Thrace.

The Fleet is stricken with an abrupt power outage as they enter the nebula, every ship affected simultaneously. With the Fleet helplessly adrift and without DRADIS, four Cylon baseships also enter the nebula and launch Raiders. Galactica detects the baseships after power is partially restored, but the Fleet's civilian ships are slower to recover and are unable to make an immediate FTL jump. Galactica responds by launching all its Vipers to intercept the Raiders, and Admiral Adama authorizes the use of nuclear weapons against the baseships.

Colonel Saul Tigh, Chief Galen Tyrol, Ensign Samuel Anders and presidential aide Tory Foster experience mutual musical hallucinations as the Fleet moves closer to the nebula. When the Fleet arrives, they are drawn together and come to realize that they are Cylons (four of the Final Five models). As a group they are able to piece together the song's melody.

Also while the Fleet approaches the nebula, Laura Roslin, Sharon Agathon and Caprica-Six share a common dream of chasing Hera Agathon in each other's presence at the Opera House. Almost immediately after arriving and coinciding with the power loss, Roslin becomes dazed or stunned, possibly because of her use of chamalla extract to induce prescient visions as in the past.

Sortied to defend against the incoming Cylon attack, Lee "Apollo" Adama picks up a mysterious intermittent DRADIS contact and breaks off to intercept it. The unknown bogey leads him on a chase through the nebula's dust clouds and, after outmaneuvering Adama's Viper, pulls up along him portside. Much to his surprise, the unknown contact is the presumed-dead Captain Kara Thrace piloting an unusually pristine Viper Mark II (Crossroads, Part II).

Notes

When an imaginary camera pulls away from the nebula into deep space, it re-enters the galaxy at roughly the same point it exited and zooms to Earth, indicating that Earth and the nebula are not very far apart on a galactic scale.
Ionia was an ancient region of southwestern coastal Anatolia (in present-day Turkey, the region nearest İzmir,) on the Aegean Sea, which was said to be founded by Ion, son of Apollo.