Galactic Standard Calendar

The Galactic Standard Calendar was the standard measurement of time in the galaxy. It centered around the Battle of Yavin as the starting point. BBY stands for Before the Battle of Yavin, and ABY stands for After the Battle of Yavin.

History
The calendar, formally known as the Galactic Standard Calendar, and also referred to as Coruscant Standard Calendar, was the main calendar in use in the galaxy since the time of the Galactic Republic. The Old Republic dated years from the Ruusan Reformation of 1,000 BBY. Prior to that, the Republic had presumably dated events from its founding in 25,000 BBY. The galactic standard for dating was once YY:MM:DD, which refers to years after the Great ReSynchronization.

The Galactic Empire used the same calendar, although they preferred to date events from the Great ReSynchronization of 35 BBY, or from the Declaration of a New Order (19 BBY).

After the fracturing of the Empire, the New Republic reclaimed the calendar. The New Republic Historical Council set the year of the Battle of Yavin to the year zero, adopting the current date system. However, it was by no means the most accepted calendar in the galaxy. It was used almost exclusively by the Rebel Alliance, the New Republic, and the Galactic Alliance. Many regions had their own calendars, including the Imperial Remnant.

It is unknown what calendar was used by the Second Galactic Empire.

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:


 * 368 days=1 year
 * 60 seconds=1 minute
 * 60 minutes=1 hour
 * 24 hours=1 day
 * 5 days=1 week
 * 7 weeks=1 month
 * 35 days=1 month
 * 10 months + 3 festival weeks + 3 holiday days=1 year

The Tapani Sector's Year

 * By the Tapani Sector's domestic calendar, which was Galactic Standard with local names, the year flowed as follows:
 * Month 1: Elona
 * Month 2: Kelona
 * Holiday 1: Tapani Day
 * Month 3: Selona
 * Festival Week 1: Expansion Week
 * Month 4: Telona
 * Month 5: Nelona
 * Holiday 2: Productivity Day
 * Month 6: Helona
 * Festival Week 2: Shelova Week
 * Month 7: Melona
 * Month 8: Yelona
 * Holiday 3: Harvest Day
 * Month 9: Relona (The Freeworlds Region of the Tapani Sector also recognized Relona 10 - 15 as Independence Week.)
 * Month 10: Welona
 * Festival Week 3: Winter Fete

The Galactic Year

 * From the above information, we can extrapolate that the year, whether Tapani-named or not, in the galaxy flowed as follows:
 * 2 months
 * 1 holiday
 * 1 month
 * 1 festival week
 * 2 months
 * 1 holiday
 * 1 month
 * 1 festival week
 * 2 months
 * 1 holiday
 * 2 months
 * 1 festival week

Although using the Tapani Calendar has proven effective, some events were recorded as occurring in month 11, as the Galactic Standard Calendar placed the festival weeks and holidays together as a form of short month.

The week

 * The week flows as follows:
 * Day 1: Atunda
 * Day 2: Katunda
 * Day 3: Satunda
 * Day 4: Datunda
 * Day 5: Natunda

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. Despite its fall into disuse within official materials and the use of the BBY/ABY notation by most of their peers, the early method of notation has caught on a small following among Star Wars fans.

When the Thrawn trilogy kicked off most of the work in the Expanded Universe, promotional material originally dated events in terms of the Battle of Endor, which made sense from an in-universe perspective of having "overthrown the Emperor" rather than victory at the Battle of Yavin. This trailed off some time after the release of The Truce at Bakura.

Time based on Coruscant is clearly a mirroring of real Earth time being modeled on the third planet from the sun.

Thursday, Saturday and Sunday have all also been mentioned as days in the EU.

It is known that the beginning of the in-universe calender does not correspond with BBY/ABY as in Fury it is stated that a new year has begun yet the book still takes place in 40 ABY just as the other books in Legacy of the Force do.