Galactic Standard Calendar The Galactic Standard Calendar was the standard measurement of time in the galaxy . It was based on the Coruscant solar cycle . The Coruscant solar cycle was 368 days long with a day consisting of 24 standard hours . Numerous were used to determine . 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 . Over time , however , historians have used numerous galaxy - changing events as epochs to mark new calendar eras . One particularly 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 ) 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 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 holiday s . As the Hyperdrive Theory allowed space travelers to bypass relativity , a single duration of time passed at all locations equally over a given interval . During the Old Republic , at least twenty variants of the Galactic Standard Calendar were in use , with the Republic Measures & Standards Bureau hotly debating which to use . One subset of the calendar , known as the 10 - month standard calendar , was used by the Republic Judiciary during the time right before the Clone Wars . Another , composed of 11 months , was utilized by the archivists , and yet another , being hexadecimal based , was utilized by infrastructure . In 23 BBY , the Republic Measures & Standards Bureau debated whether to keep this calendar as one of the twenty or so official calendars of the Republic , with Keelen Ma commenting that the various researchers were getting tired of needing calendar converters on their pads . Days of the week . Some locales had other names for days of the week , including Thursday and Saturday . Behind the scenes . BBY / ABY is sometimes known as BSW4 / ASW4 , which means " before / after " . 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 acronyms altogether and listed dates as YEARS , with 0 YEARS being the events depicted in Episode IV . The first to use the BBY / ABY notation was " The Essential Chronology " . This practice continued in " The Essential Guide to Alien Species " and beyond . Material promoting " " and other contemporary works dated those works by specifying how much time had passed since the Battle of Endor . This practice began to change after the release of " The Truce at Bakura " . In 2005 and 2006 , Karen Traviss stated 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 " . " " mentioned Sunday school , but gave no indication it was named for a day of the week . 12 - month / 368 - day year structure . The number of days in every month has yet to be revealed .