BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
The Youtini Expanded Universe Ranking system is a 1-5 scale that ranks EU book quality, difficulty, and importance. Books closer to Level 1 are easier to read and understand, more important, and of higher quality.
Emperor Palpatine has a new weapon—one that can annihilate a planet. But he's not targeting a planet—he's targeting the future of the Jedi, Leia's children. It looks like a hopeless situation for Luke Skywalker, who has the critical task of protecting the children. But it's not the first time Luke has found hope where none existed. The finale to the Dark Empire trilogy is collected here.