Galactic Standard Calendar

The Galactic Standard Calendar was the standard measurement of time in the galaxy. It centered around the Coruscant solar cycle. The Coruscant solar cycle was 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 used the Battle of Yavin as its epoch, or "year zero". BBY stands for Before the Battle of Yavin, and ABY stands for After the Battle of Yavin.

History
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 epoch to mark new calendar eras.

One particularly notable epoch is the Treaty of Coruscant of 3,653 BBY. The calendar eras before and after this event (referred to as "BTC" and "ATC", respectively) 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 1,000 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 rise 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 year 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.

Time measurement
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 satellite 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 year was 368 days, composed of ten months, three fete weeks, and three holidays. As the Hyperdrive Theory allowed space travelers 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

 * 1) Primeday
 * 2) Centaxday
 * 3) Taungsday
 * 4) Zhellday
 * 5) Benduday

Behind the scenes
BBY/ABY is sometimes known as BSW4/ASW4, which means "before/after Star Wars Episode IV". The BSW4/ASW4 notation was used in the timeline of the second edition of A Guide to the Star Wars Universe and The Essential Guide to Vehicles and Vessels. The Essential Guide to Planets and Moons eschewed any acronyms altogether and listed dates as YEARS, with 0 YEARS being the events depicted in Star Wars Episode IV. The first Essential Guide to use the BBY/ABY notation was The Essential Chronology. This practice was continued in The Essential Guide to Alien Species and beyond.

From an in-universe perspective, the overthrow of the Emperor makes more sense as an epochal marker than victory at the Battle of Yavin. Indeed, promotional material surrounding the Thrawn trilogy and other contemporary works reckoned time in how much had passed since the Battle of Endor. This practice began to change some time after the release of The Truce at Bakura.

Thursday and Saturday have also been mentioned as days in the Expanded Universe, and Sunday as a type of school.

In 2005 and 2006, Karen Traviss revealed that she used the 10-month calendar when writing her Republic Commando novels.

The Essential Atlas featured years of 12 months and months of 30 or 31 days, as did The New Essential Chronology.

There is not a difference in months between the Galactic Standard and the Great ReSynchronization and no conversion is necessary between the two. A seeming confusion on this matter by a minority of fans, perpetrated primarily by Nathan Butler's Star Wars Timeline Gold (which itself is a fanmade project), has resulted in some inconsistencies arising and creeping into published sources when dealing with previously well established timeframes. For example, while the Great ReSyncronisation Date of 42:2:17 for the Liberation of Coruscant depicted in X-Wing: Wedge's Gamble may be correct, the common assumption that this took place in 6 ABY is wrong (given the in-text references to both Tycho's capture and the events of Yavin being over 7 years ago). The liberation actually takes place in the second month of 7 ABY. This is backed up by The Essential Atlas and The Essential Reader's Companion, which places X-Wing: Wedge's Gamble in 7 ABY. Comments by Sue Rostoni made in 2006 on her StarWars.com blog also indicate no difference in months between the two dating systems.

Recent sources (The Essential Atlas & The Reader's Companion) have led to the assertion that events denoted by 0 BBY & 0 ABY occur as part of the same year - Year 0. Events denoted by BBY occur before the Battle of Yavin in Year 0 and events denoted by ABY occur after The Battle of Yavin within Year 0; therefore both periods occur within the same year - Year 0. The specific terms BBY & ABY are only used to indicate if an event occurs before or after The Battle of Yavin within the Year 0. To clarify, there is not a zero year on either side of the Battle of Yavin. Events in 1 BBY occur in the year before the year in which the Battle of Yavin occurred; 2 BBY - the second year before the Battle of Yavin; and so on. The Essential Atlas gives a date of 35:3:3GrS for Star Wars: A New Hope; this translates the specific events of A New Hope as starting 3 Months and 3 days into the Year 0. Events occurring within 1 BBY translate into 34GrS while 1 ABY translates to 36GrS. The actual start of this zero year is approximately 3 months before the Battle of Yavin; in alignment with the Great ReSynchronization. While the Battle of Yavin was the initial catalyst for the change in the galactic standard calendar, this event occurs within the Year 0 rather than becoming an absolute zero date. This is evidenced particularly by stories occurring within Year zero but chronologically prior to the Battle of Yavin such as Interlude at Darkknell. The recent clarification is much the same as in the numerous real world calendar's in the real world; significant events may lead to the creation of a new starting year but very rarely does an event become the first day of the first year of the new calendar as they are primarily dictated by the solar cycle. As the solar cycle cannot be changed, the relative starting date of a year does not change.

12-month/368-day year structure
The twelve month calendar may adopt the same number of days per month as the Gregorian calendar with the exception of Month 2 to accommodate the 368 day year. However, the number of days in every month has yet to be revealed.


 * Month 2 has at least 29 days, and as many as 31 to accommodate the extra 3 days in the calendar.
 * Month 5 has 31 days.
 * Month 7 has 31 days.
 * Month 10 has 31 days.