The Galactic Standard Calendar is the standard measurement of time in the galaxy. It centered around the Coruscant solar cycle, which is 368 days long with a day consisting of 24 standard hours. Numerous epochs are used to determine calendar eras. The most recent of these calendar eras used the Battle of Yavin as it's epoch, or "year zero". BBY stands for Before the Battle of Yavin and ABY stands for After the Battle of Yavin.
The calendar, also referred to as the Coruscant Standard Calendar, was the main calendar in use in the galaxy since the time of the Galactic Republic. Presumably the Old Republic dated years from its founding in 25,053 BBY. Throughout time, however, historians have used numerous galaxy changing events as epochs to mark new calendar eras.
One particular notable epoch is the Treaty of Coruscant of 3653 BBY. The calendar eras before and after this event (referred to as "BTC" and "ATC," respectively, as a result of the Galactic Calendar) were popularized by the famous Jedi historian Gnost-Dural. His holographic records, which used this numbering system, contained some of the most complete records of numerous important events such as the Hundred-Year Darkness, the Great Hyperspace War, the Great Sith War, the Mandalorian Wars, the Jedi Civil War, and the Great Galactic War against the returned Sith Empire. For this reason, this method of numbering years remains important to historians.
Other notable epochs used were the Ruusan Reformation of 1000 BBY, the Great ReSynchronization of 35 BBY, the formation of the Galactic Empire in 19 BBY, and the Battle of Endor in 4 ABY. With the exception of the Ruusan Reformation, the later epochs were all within the same century and stemmed from the events and upheavals surrounding the ruse and fall of the Galactic Empire. They were short-lived and used by various historians at the time. In 25 ABY, the New Republic commissioned the New Republic Historical Council to re-standardize the Galactic Calendar. The historical council chose the Battle of Yavin, instead of the Battle of Endor, calling the former the more significant galactic event. From that point on, the years in which the Battle of Yavin occurred was the epoch used for the dating system. It was used by the New Republic as well as the subsequent Galactic Alliance. Many regions, however, kept their own calendars, including the Imperial Remnant.
The calendar was based on the size and rotation of the planet Coruscant. It was a luno-solar calendar based both on Coruscant's orbit around its sun, and the orbit of its primary satellie Centax-1. The standard unit of time was the standard second. Sixty standard seconds made up each standard minute, and sixty minutes made up each standard hour. Each day consisted of 24 standard hours. A standard week was 5 standard days, and each month was seven weeks (making 35 standard days each month). A standard years was 368 days, composed of ten months, three fete weeks, and three holidays. As the Hyperdrive Theory allowed space travellers to bypass relativity, a single duration of time passed at all locations equally over a given interval.
In the galaxy:
- 60 seconds = 1 minute
- 60 minutes = 1 hour
- 24 hours = 1 day
- 5 days = 1 week
- 7 weeks = 1 month
- 35 days = 1 month
- 368 days = 1 year
- 10 months + 3 festival weeks + 3 holidays = 1 year
Days of the week