Every locality is going to measure time according to their particular astrometry--that's just common sense. But to coordinate events happening in multiple localities--or in deep space, for that matter--there needs to be a single, unified system, meeting all the following criteria:

• Not dependent on local clocks, which can be made unreliable by relativistic travel
• Not dependent on communication, which can be time-shifted by relativity, or may be comprised by enemy factions
• Not entirely reliant on star observation, lest it be useless where stars are not observable

How It Is Determined

The best candidate so far:

• A reconciliation of several sources:
  • Pulsar Clock: extremely reliable and simple, but only works where the radio signals of pulsars can reach, and said rays can be perturbed by spacetime fluctuations
  • Gravimetric Galactic Clock: the movement of the galactic core around its barycenter with various orbiting stars and masses produces a subtle "wobble", measurable by gravity wave detectors. The wobble is a chaotic pattern that never repeats, but can be mathematically predicted, and thus observing the pattern for a relatively short time can yield absolute galactic time. The gravity waves of such an object overpower the noise of local spacetime perturbation. Usually, gravity wave detectors are massive devices, larger than planets; however, any functioning warp drive can detect powerful gravity waves--a vital feature to keep the warp bubble stable. Conveniently enough, the most common scenario where pulsar clocks are unreliable is during warp travel, when gravimetric galactic time becomes measurable.

How It Is Measured

In native form, galactic time is represented as a Galactic Time Code, defined as the number of picoseconds elapsed since the arrival of the colony ships in Homeworlds space, as measured by a theoretical clock in perfectly flat spacetime.

For example, the GTC corresponding to the first moment of the year 2808 is 26,444,707,200,000,000,000,000

(Note: GTC cannot be processed natively by 64-bit processors. This is not a problem in the 29th century)

Every planet has its own orbital and rotational periods, so there is no physical, universal concept of "years", "months", or "days". That being said, they are convenient units in which to think. For this purpose, Galactic Standard Time defines a number of units of time measurement:

This calendar approximates the calendar of Earth, with the advantage of being partially decimalized. As it is based on the Julian Year, as opposed to the mean sidereal year of Earth, it drifts by several days per millennium, but otherwise allows for reasonably accurate timekeeping relative to Earth norms.

The year is the only particularly complex unit. It is defined as follows:

• Each month is exactly 28 days (4 weeks).
• There are twelve proper months, three per quarter.
• After each three months, there is an interstitial week that does not belong to any month.
• Thus, each quarter is of exactly the same length (13 weeks).
• After all four quarters (twelve months plus four extra weeks), there is an additional leap day not belonging to any month or week. Every 4 years, there are two instead of one.

The numbering of years is synchronized with the Earth calendar (as reconciled using the Galactic Clock). Thus, GST-2808 occurs at the same time as 2808 CE on Earth.

GST does not define names for months, days of the week, etc, as traditionally the calendar was not used for ordinary timekeeping.

GST is represented as follows:

• The broadest unit is always first. Year comes before month, month before day, etc.
• Periods separate each unit of date and time.
• Dashes or spaces separate date from time.
• The prefix "GST-" is preferred.
• Dates are represented as year.quarter.week.day.
• Times are represented as hour.minute.second.optional subsecond.
• Date and time can be represented alone (i.e. without the other). Year must always be 4 or more digits, while hour can never be more than 2, so the number of digits in the first element indicates whether it is a date or a time.
• Year, quarter, week, day, and hour begin at 1; they have no 0 value.
• Minute and second begin at 0.
• Examples:
  • GST 2808.2.12.6 19.45.06 is the year 2808, quarter 2, week 12 (aka month 6 week 4), at 19 hours, 45 minutes, 6 seconds.
  • 2808.4.13.7 is the last day of the last interstitial week of 2808.
  • 2808.4.14.1 is the leap day at the end of 2808.

Foundation Standard Time

Since the Foundation began, there now exists an entire contiguous culture living in space full-time, with no reference planet. The Foundation has adopted Galactic Standard Time as their calendar, with several extensions:

• Days of the week are named.
  • Officially, the names are Prima (1), Secundus (2), Tertia (3), Quartus (4), Quinta (5), Sextus (6), Septimum (7).
  • Given the strongly Karman leanings of early Foundation culture, most people use the Karman names, which incidentally are the same used on Earth.
• Months are named.
  • ...
• Interstitial weeks are national holidays.
  • Where feasible, most employers grant these weeks off.
  • Each week hosts a seasonal festival. There are no seasons in space, but the traditional value outweighs the practical consideration.
  • Spring Festival follows March, Summer follows June, Fall follows September, and Winter follows December.
• The leap day is known as New Year's Day, and is a national holiday.
  • The second leap day is also a holiday, and occurs before the normal leap day. It is known as Leap Day.
  • During years with no Leap Day, the day before New Year's Day is a holiday.
• In addition to the GST standard date format of year.quarter.week.day, FST adds an alternate form, used more commonly in every day life:
  • Numeric form: Year.month.day, i.e. 2808.5.25
  • Verbal form: 2808-May-25
  • Interstitial: Year.week.day, i.e. 2808.13.5. Colloquially, "Friday, Spring Festival"