Colonial calendar

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A hypothetical Colonial calendar would be common to the Twelve Colonies, but aside from their use of terms such as "day," "month" or "year," there is little information about a system from which the units would theoretically derive. We don't even know whether all the colonies use one method, as opposed to individual, colony-based calendars.

Specific dates were usually avoided in the re-imagined series; the most detailed depiction of an actual calendar comes from the dossier of William Adama's career in the episode "Hero" (see below). Dated props such as memos, awards, letters and similar items were photographed for various auctions, revealing styles of dates ranging from seemingly random alphanumeric strings to inconsistent year numbers. The diversity of dates strongly suggests that no definite system had been established for the re-imagined series.

On the other hand, the Caprica series and its associated materials contain prominent and much more consistent references on the same kinds of items, indicating that the producers eventually worked out a method which is based on the Roman calendar. Dates in that style were also used in the Syfy blog The Caprican, which therefore revealed much of the basic calendar structure. However, since the series rarely took us to other colonies, it remains unclear whether the calendar is specific to the planet Caprica or common to the twelve worlds.

Units of Time

The units used to express timespans in the re-imagined series and Caprica appear to be identical to those of the Gregorian calendar, with 24-hour days and approximately 365-day years. The best example of this is in "Tigh Me Up, Tigh Me Down," where Baltar says that each of his tests takes 11 hours. As there are 47,905 tests, amounting to 526,955 hours' worth of tests, this would have taken him 21,956 days or 60.1534 years (as confirmed by Baltar's Messenger Six).

Weather forecast featuring all seven days of the week

Although the calculation uses an average year of 365 days, without taking into account leap years, it could be due to a mistake rather than a deliberate revision. A year comprising 52 weeks is revealed in "Rebirth" during the airing of a Cubits & Pieces clip. Further, days of the week are gradually introduced in this and later episodes: Saturday (CAP: "Rebirth"), Monday (CAP: "Gravedancing") and Wednesday (CAP: "Ghosts in the Machine"). All seven days are finally shown onscreen as part of a weather forecast (CAP: "Retribution").

Ronald D. Moore addressed the units of time on his blog: "I dropped many other terms from the old show like 'centon' (a unit of measurement) and 'yahren' (year) because I felt they distracted from the mood I was trying to create and they sounded a bit silly to my ear." Nevertheless, the word yahren does appear in the Cylon specifications examined by the Armistice Officer (TRS: "Miniseries, Night 1").

The Calendar from Caprica

Building upon the units described above, Caprica introduced its own system which is relatively consistent and widely used on various props.


Recent years are two-digit numbers, almost always preceded by the letters YR. Several common formats are listed below:

  • YR01
  • YR 01
  • yr01
  • 01YR

Apart from its epilogue and flashbacks, Caprica is set in YR42. Years before YR0x are expressed as YR9x, while ancient dates can be longer than two digits and designated "byr". SergeGraystone explained that "YR means 'year' and 42 represents the last two digits of the year." When asked about the era, he stated that the present day is "1,942 years since the human exodus from Kobol."


The table below collates months and days per month from all sources, matching them to the Gregorian calendar.

Ianuarius at least 23 January
Februarius at least 27 February
Martius at least 30 March
Aprilis at least 24 April
Maius at least 27 May
Iunius at least 27 June
Quintilis at least 25 July
Sextilis at least 14 August
September at least 23 September
October at least 29 October
November at least 16 November
December? at least 26? December

The most frequent names are identical to those in the Roman calendar, but there appear to be variations as well: Junius, June, Aprilus, Sextilius.

Date format

The date components can be formatted in many different ways. Some examples, in no particular order:

  • Sextilis 8, YR42
  • 8 Sextilis YR42
  • 08/08/yr42
  • 08-08-42YR
  • 08/08/42

Evidence from the series

Revised Caprica pilot


Reins of a Waterfall

  • The recording of Ben Stark's interrogation is dated "APRILUS 9TH YR41". Agent Jordan Duram says that it was made a year ago.
  • Moments later, Duram looks at what appears to be the current issue of Caprican Tribune, which is dated "Aprilis 11, YR 42". Although illegible onscreen, "November 26" is given as the MagLev bombing date (CAP: "Reins of a Waterfall," Propworx).


  • Daniel Graystone says he made a Solstice wish for free publicity, referencing Baxter Sarno's previous coverage of the Graystone family (CAP: "Gravedancing"). Since The Caprican has placed the Vernal Break in Martius, analogous to the vernal equinox in March on Earth, Daniel's line could be taken as supporting evidence for the Junius timeframe from "Rebirth". Solstices on Earth occur around June 21 and December 22.
  • Ross Farmo's staff badge on Backtalk with Baxter Sarno contains the note "EXP. 08 YR 44". The badge apparently expires in Sextilis YR44 (Propworx).
  • Sandhano Schultz's badge from the same talk show is marked "EXP.09 YR 45" (Propworx).

Know Thy Enemy

  • Joseph Adama asks Evelyn to identify Tad Thorean based on black-and-white photographs with timestamps, where the date component almost certainly reads "YR:42:02:22".
  • Tad Thorean's date of birth is given as "06-04-27YR" on his driver's license, which also contains less readable dates of issue and expiration (CAP: "Know Thy Enemy").
Guides to artifacts dated at around "400 byr".
  • The Art Treasures of Kobol pamphlet by the Caprican Art Museum dates three artifacts at "Circa 400 byr". The "yr" and the exhibit run from "IUNIUS 15 THROUGH QUINTILIS 25" suggest that the year was intended to fit within the established calendar. If SergeGraystone's data is correct, the simplest explanation would be 400 years before the current era, which began 1,942 years ago with the exodus from Kobol (Propworx).

The Imperfections of Memory

Ghosts in the Machine

  • Tamara Adama's signature is found near a poster opposite the gun check-in booth in the virtual club visited by Joseph Adama and Emmanuelle. The poster promotes an event "Exclusive to The Eleusinian Theatre Throughout the month Of Maius" (CAP: "Ghosts in the Machine").

End of Line

  • The deadline for Daniel Graystone to deliver 100,000 robots was moved up to "the seventh," which is "next week" (CAP: "End of Line"). The episode also establishes the existence of a holiday named Eros Day, which was first mentioned in articles of The Caprican posted in February 2010, a month before the episode aired, and is a clear parallel to St. Valentine's Day.


  • Daniel Graystone, Joseph and Sam Adama review Lillian Teller's personnel file which contains "7 Iunius YR 38" as the "start" date, presumably for when she started as director. In addition, a less readable year is briefly shown in the previous employment section of the document (CAP: "Retribution").

Things We Lock Away

False Labor

Duram's files.
  • Duram's files contain a number of dates which aren't fully legible at this point. From the document on Clarice Willow:
    • "PRINT DATE" (?) "09/26/yr42" (?)
    • "FILE DATE" (?) "09/27/yr42" (?)
    • "BORN" (?) "01-28-YR04" (?) (her age is given as 37)
    • "Year Grad" (university?) "29YR" (?)
  • An included photo appears to point out the place where Hippolyta (?) Androgeus' (Hippolyta's?) corpse was found. The numbers "23/09/42" are associated with the circled location. Although 'YR' is missing, the figures are consistent with the first two dates in Willow's file (Propworx).
  • An edition of Caprican Tribune was published on "JUNE 28, YR42" (Propworx).
  • The Caprican Comic Pages read by William "Willie" Adama are dated "JUNE 22, YR42" (Propworx).


Here Be Dragons

  • Joseph Adama ("Shay Ross Hilliard") was born on Sextilis 8, YR93 according to his falsified birth certificate, passport and driver's license. The latter uses the same format as Tad Thorean's, 08-08-93YR, confirming that Sextilis is indeed the eighth month. More importantly, YR93 doesn't contradict SergeGraystone's comment that YR is followed by the last two digits of the year. However, the driver's license was issued 04-01-43YR, which is inconsistent with the prevailing YR42 (Propworx).
  • Sam Adama ("Ross Bailey Framo") was born on Iunius 11, YR92 according to his falsified birth certificate. However, Framo's driver's license appears to give his date of birth as 08-11-? as opposed to 06-11-92YR. The 08 might be a leftover from Joseph's falsified driver's license (Propworx).


  • Daniel pronounces his access code as "Wye-Ar-25-Zeta-Theta-Epsilon," where the Greek letters spell out ΖΘΕ. If YR25 is Zoe Graystone's year of birth, she would've celebrated her seventeenth birthday in YR42.
  • A scrolling digital announcement in the Atlas Arena reads "BE HERE FOR THE NEXT HOME GAME ON IUNIUS 27TH!" (CAP: "Apotheosis"). Since the exact same text was also used in the pilot and we've seen several games in the meantime, it probably shouldn't be taken literally.
  • Tickets to the Caprica Buccaneers vs. Delphi Legion game are dated "SEXTILIS 11, YR42" (Propworx).
  • Tickets to the Caprica Buccaneers vs. Gemenon Twins game are dated "IUNIUS 10, YR42" (Propworx).

Unknown episodes

  • A packet entitled U-87 Circuitry Specifications was "ISSUED 10 OCT." (Propworx).
  • The "FILE DATE" on Mar-Beth Willow's GDD file is "12/26/yr42" (Propworx).

Pyramid posters

The Profiles in History auction of four posters from Daniel's private game box revealed a number of playoff dates, confirming the months of Quintilis and September. In some of the layouts, the 'YR' prefix is written with a smaller font size than the rest of the date, indicating a possible stylistic alternative.

  • APRILIS 6, YR37
  • APRILIS 11, YR37
  • QUINTILIS 22, YR37
  • SEPTEMBER 11, YR37
  • Iunius 12, YR37 ['YR' prefix with a smaller font size]
  • MARTIUS 19, YR39
  • MARTIUS 27, YR39
  • MAIUS 22, YR39
  • MAIUS 27, YR39
  • IUNIUS 5, YR39
  • IUNIUS 27, YR39
  • Quintilis 25, YR39 ['YR' prefix with a smaller font size]

Analysis of William Adama's Dossier

Adama's dossier (TRS: "Hero")

In "Hero," William Adama's dossier can be clearly seen. While this document is fairly accurate in terms of Adama's personal history, the calendar scheme used in the document seems to be flawed, particularly in lieu of previously established methods of timekeeping demonstrated in the series.

Here are a list of dates from Adama's past that Adama's dossier contains:

Dossier Date Notation BCH/YR Notes
H5/21290 Birth of William Adama 58 BCH (42YR)
D6/21311 First commission, Battlestar Galactica, fighter squadron 42 BCH (58YR) How this relates to his prior assignment on Raptor 909 and its participation in Ghost Fleet Offensive remains unknown (TRS: "Blood & Chrome")
E4/21312 Commendation for shooting down Cylon fighter in first combat mission. 40 BCH (60YR) This would tie directly to the events of the Operation Raptor Talon, where Adama has his first engagement in a Viper (TRS: "Razor Flashbacks")
D5/21314 Mustered out of service post-armistice. 38 BCH (62YR)
R6/21317 Served as Deck Hand in merchant fleet and as common […] aboard inter-colony tramp freighters 35 BCH (65YR) Seen fleetingly in flashbacks (TRS: "Scattered").
D1/21331 Recommissioned to Fleet 23 BCH (77YR)
D6/21337 Major: Battlestar Atlantia 17 BCH (83YR)
R8/21341 Executive Officer: Battlestar Columbia 13 BCH (87YR)
C2/21345 Commander: Battlestar Valkyrie 9 BCH (91YR)
C2/21348 Commander: Battlestar Galactica 6 BCH (94YR) This would place his reassignment shortly after the ill-fated mission where Daniel Novacek is believed KIA over the Armistice Line (TRS: "Hero").

This provides some interesting information. The fields in the format X#/##### appear to be dates, with the five-digit string following the solidus apparently corresponding to the year.

The following can be deduced from this document:

  • This episode marks the 45th anniversary of Adama's commissioning, which puts it in the year 21356 and makes Adama 66 years old. On the other hand, he was born at least several months after the Caprica pilot, which is set in 58 BCH (42YR) (CAP: "Apotheosis").
  • Adama spent three years in between being mustered out and finding a job on a tramp freighter. We may speculate that it was during this time that his relationship with first wife Carolanne Adama deteriorated.
  • Adama spent a total of 14 years serving in the merchant fleet.
  • Adama met Tigh roughly 30 years ago (TRS: "Torn"). That would be 21326, which correctly puts it in the middle of Adama's merchant fleet service.
  • Adama was a major by the time he arranged for Tigh to be reinstated in the fleet (TRS: "Scattered"), which means that at least six years passed in between Adama's recommissioning and Tigh's.
  • Ronald Moore stated in his podcast for "Scattered" that the flashback scenes in that episode took place 20 years before that episode, or in 21334. In fact, they appear to span at least an eleven-year period between 21326 (Adama and Tigh's first meeting) to 21337 (Adama's promotion to Major).
  • The first Colonial Day, marking the unification of the Colonies, was probably in 21302. The one celebrated in "Colonial Day" was the 52nd, and it is now two years later.
  • Galactica herself is at least 45 years old. Other battlestar's minimum ages prior to the Fall: Atlantia at least 13, Columbia at least 11, and Valkyrie at least 8.

Additionally, an error occurs in "Hero." Dialogue from this episode claims that Adama served on Valkyrie one year prior to the Fall of the Twelve Colonies, putting the date of Lt. Daniel "Bulldog" Novacek's capture at 21352-53. However, Adama's command of Valkyrie ended in 21348, which means that Adama commanded Galactica for eight years. It has already been established in dialogue from the Miniseries, "Act of Contrition," and "The Farm".

Inference about calendar structure

If the five-digit string following the solidus is in fact the year, as seems inescapable based on the above, the letter-digit sequence before it must indicate the position in the year. There are 260 unique letter-digit sequences of that format, which may indicate a shorter year in the calendar, essentially a year of twenty-six ten-day weeks. However, what has been revealed about Colonial timekeeping is too incomplete to draw any conclusions.

However, if the above is to be inferred, a striking inaccuracy occurs because of this service record. Prior episodes have firmly established that the Colonial year is analogous to one Earth year of 365 days. In "Tigh Me Up, Tigh Me Down," the Cylon detector takes 11 hours to thoroughly test each blood sample. As there are 47,905 tests (526,955 hours) this will take him 21,956 days, which Six then computes will take approximately 60 years, the same as it would here. The timespans further established in "Lay Down Your Burdens, Part II," "Battlestar Galactica: The Resistance," and "Occupation" also support this comparison.

On the other hand, the Colonial numerical system may start with the numbers zero through 99, then continue with A1 through Z9, followed by AA, AB and so on. This would mean that the first day of the year is 1 and the last day, the 365th, is represented as AF.

It is astonishing to learn that the Colonials have—or believe they have—over 21,000 years of recorded history. By comparison, Pythia was said to have recorded her prophecies 3,600 years ago (TRS: "The Hand of God") and the Great Exodus from Kobol took place just 2,000 years ago. On Earth, Human civilization is only about 6,000 years old.

Other Calendars

The system used in the dossier is only the most prominent example of dates in the re-imagined series. A closer analysis of other items reveals a number of different methods. It is unclear whether these were actual calendar proposals or random alphanumerics which were never intended for closer inspection.

  • The note "SEVENTH MILLENNIUM OF TIME" appears on paper cubits. It comes from President Adar's toast in the original series pilot: "As we approach the seventh millennium of time, the human race at last will find peace, thanks to you."
  • Lee Adama's date of birth is "432:979:021" according to his service record.
  • William Adama was "to report to Aerilon High Command, Base 12 at 038:847:857" in his letter of reinstatement in the Colonial Fleet. His shuttle was scheduled to leave for Aerilon "at 024:639:374".
  • The incident report on the murder of Jack Fisk is dated "134-2367". The text contains references which appear to be dates: "On 25372- sometime after a meeting with President Laura Roslin ... Commander Jack Fisk returned to his quarters ... At approximately 24367-47 Officer Hoshi, after mustering his officers for their daily briefing, proceeded to Commander Fisk's quarters ..."
  • Gaius Baltar's executive order concerning settlement on New Caprica became law "this 23rd day of 04859".
  • Baltar's Proclamation of Illegal Arms is dated "R767-87," and the exact same date also appears on the Acquisition of Firearms for the New Caprica Police Academy memo.
  • Adama's resignation letter at the end of "Hero" appears to be dated in an entirely different format compared to the system used in his dossier. While difficult to read clearly, it appears to be dated "27/S9/9F23". On the other hand, this may not be a date but some form of document ID number.
  • In addition, the execution order written by the Cylon Occupation Authority and signed by then-President Gaius Baltar is dated "this second day of 3454-91" (TRS: "Occupation"). This may be a date on the Cylon Calendar but this would not explain why the Cylons wanted this "official" document to use their timekeeping system instead of that used by the Colonials.
  • Kara Thrace's disciplinary record in "Maelstrom" notes that a proceeding was "held on 22/E4/3F3". This appears to be a date, but there is no confirmation.
  • The medal of valor given to Socrata Thrace uses a day number and alphanumerics to specify the current date ("this day of ..."), whereas Socrata's period of service is expressed using two sets of alphanumerics. The exact numbers and letters are currently unreadable.
  • A store sign in New Cap City reads "QUALITY JEWELRY SINCE 1952" (CAP: "The Imperfections of Memory"). It is unclear whether the year is related to the calendar from Caprica, especially if SergeGraystone's 1,942-year era is correct.