Star Wars: Destiny of Rebirth
The Galactic Standard Calendar is the standard measurement of time in the galaxy. It centers around the Coruscant solar cycle. The Coruscant solar cycle is 368 days long with a day consisting of 24 standard hours. Numerous epochs were used to determine calendar eras. The most recent of these calendar eras uses the Battle of Yavin (ext) as its epoch, or “year zero”. BBY stands for Before the Battle of Yavin, and ABY stands for After the Battle of Yavin.