Stardate
A stardate was a date in a variety of systems employed by the United Federation of Planets and other societies. It was usually expressed as a number of digits with a decimal separator, e.g. 5928.5 or 2263.02.

History 

Stardate systems were used in certain cultures as early as the 2150s, when the United Earth government worked with calendar dates. In 2154, Degra, a Xindi-Primate, sent a coded message to  containing a stardate for when Enterprise should rendezvous with Degra's ship. T'Pol knew that it was three days in the future, indicating that Vulcans also had an understanding of stardates at that time. () In the late 2250s, the Terran Empire used them to date events of 2155. ()

By 2164, Starfleet officers would open log entries with a stardate. By 2230, the first four digits stood for the Gregorian calendar year. In the alternate reality of stardate 2258, the  gave its manufacturing date as "stardate 2387". () This scheme was used in the alternate reality as late as 2263. () By 2256 in the prime reality, a more opaque relationship had been established between stardates and the Gregorian calendar. () Variations on this scheme were used as late as 3188. ()

Stardates did not replace clock time or everyday units for expressing larger timespans, such as days, weeks, months, years, centuries, or millennia, and stardate systems tend not to apply retroactively instead of Gregorian or Julian calendars either. ()

Examples
The following table outlines the progress of stardates over time:

In an alternate timeline that diverged from the prime timeline in 2344, the term combat date had replaced the term stardate in the dating system used by Starfleet by 2366. The term was used during the  of that timeline. ()

Appendices

Background information 
Stardates were first portrayed in , the second pilot for the series. Dave Eversole notes that the first draft of the teleplay (dated May 27, 1965) includes "Captain's Log, Report 197."  In addition,   shows a scripted narration from the same draft containing "star date 1312.6". This became "star date 1312.4" by the final revised draft (July 8, 1965), which also asks for "C-1277.1 to 1313.7" to appear on Kirk's gravestone. According to Star Trek Fact Check, de Forest Research had this to say about stardates:

(Page 2, Scene 3) 
But on star date 1312.4 – Astronomers already have adopted a method of dating which makes possible the counting of the number of days elapsed between widely separated observations called 'the Julian Day'. Today July 14, 1965 is 2,438,956 in Julian days. A Julian cycle is 7,980 years, and the Julian day measurement would be scientifically authentic. Suggest "on Julian B 1312.4". This date would be August 5, 3271.

(Page 65, Scene 175) 
C-1277.1 to 1313.7 – We presume dates are in days, Kirk would only be 36 days old. For conventional dating suggest 3235 to 3271. For Kirk's birth date in Julian system figure would be in millions. If desired, can be calculated.

On the other hand, the letter "C" and the rate of increase in the script suggest that 1277.1 was intended to be the date Kirk was promoted to captain and/or assumed command of the Enterprise, not his date of birth. Julian B is meant to be the day count since January 1, 3268, the start of the next 7,980-year 

According to Kellam de Forest:
"The original script for the pilot of Star Trek was titled "Menagerie" (sic) and we in the research department, De Forest Research, didn't see it until it was in script form and came to us to review just like any other Desilu script, or any other script from any other client. So we got this script, and the script originally had dates in it, like 2362, and months and days. I felt that that sounded a little awkward for the 23rd, 22nd century, so I thought that there should be another, another dating system. So I checked that, yes, the astronomers had a way of dating called a Julian day system, in which, based on the calculations of a 16th century French mathematician/philosopher that felt that because he devised this calendar with a thousands and thousands of year cycle and each day was numbered, and astronomers have used that since, because it, you don't have to bother with years and leap years and AD and BC. So I suggested to Gene Roddenberry that there was this system out there and the days would be numbered, and he picked up on that and coined the term "stardate" and dated the log and the dating in Star Trek with this stardate system."

Gene Roddenberry: The Myth and the Man Behind Star Trek  
The second pilot was written by Samuel A. Peeples, who was interviewed by journalist Joel Engel for Gene Roddenberry: The Myth and the Man Behind Star Trek.  Replying to a newsgroup question on stardates, Engel quoted information from his book:

"For the starship captain's log entry narrations, Roddenberry wanted to devise a futuristic measurement of time reference. He called (Sam) Peeples (whom Roddenberry had contacted early on for help in learning about science fiction, a subject he knew nothing about; it was Peeples who wrote "Where No Man Has Gone Before," the pilot that sold ST). The two men had a few drinks while brainstorming, and soon began chuckling over their imaginative 'stardate' computations. 'We tried to set up a system that would be unidentified unless you knew how we did it,' Peeples says."

"They marked off sections on a pictorial depiction of the known universe and extrapolated how much earth time would elapse when traveling between given points, taking into account that the Enterprise's warp engines would be violating Einstein's theory that nothing could exceed the speed of light. They concluded that the 'time continuum' would therefore vary from place to place, and that earth time may actually be lost in travel. 'So the stardate on Earth would be one thing, but the stardate on Alpha Centauri would be different,' Peeples says. 'We thought this was hilarious, because everyone would say, "How come this date is before that date when this show is after that show?" The answer was because you were in a different sector of the universe.'"

The Star Trek Guide 
The following instructions to writers were copied from the series bible Star Trek Guide; they are quoted at Star Trek Fact Check.  The original date of composition and the author are unclear, but the sample stardates are consistent with the range from the second pilot.

"We invented "Stardate" to avoid continually mentioning Star Treks century (actually, about two hundred years from now), and getting into arguments about whether this or that would have developed by then. Pick any combination of four numbers plus a percentage point, use it as your story's stardate. For example, 1313.5 is twelve o'clock noon of one day and 1314.5 would be noon of the next day. Each percentage point (sic) is roughly equivalent to one-tenth of one day. The progression of stardates in your script should remain constant but don't worry about whether or not there is a progression from other scripts. Stardates are a mathematical formula which varies depending on location in the galaxy, velocity of travel, and other factors, can vary widely from episode to episode."

What is called a "percentage point" is actually the tenths digit. While the daily rate of increase wasn't always adhered to within episodes, the initial four digits weren't selected quite as randomly as described here. An overall increase with time can be observed in the above table of stardates, from 1312.4 in the second pilot to 5928.5 in the final episode of the series. The Animated Series and the movies continued the general trend, despite a number of variations in the rate of change.

The Making of Star Trek 
Although much of the information from the Star Trek Guide was used in Stephen E. Whitfield's book The Making of Star Trek (conceived in May 1967 and published in September 1968), the above specifics of selecting stardate numbers weren't included. However, the author did interview Gene Roddenberry on the subject, who provided a more elaborate rationalization for stardate behavior:

"In the beginning, I invented the term "star date" simply to keep from tying ourselves down to 2265 A.D., or should it be 2312 A.D.? I wanted us well into the future but without arguing approximately which century this or that would have been invented or superseded. When we began making episodes, we would use a star date such as 2317 one week, and then a week later when we made the next episode we would move the star date up to 2942, and so on. Unfortunately, however, the episodes are not aired in the same order in which we filmed them. So we began to get complaints from the viewers, asking, 'How come one week the star date is 2891, the next week it's 2337, and then the week after it's 3414?'"

"In answering these questions, I came up with the statement that "this time system adjusts for shifts in relative time which occur due to the vessel's speed and space warp capability. It has little relationship to Earth's time as we know it. One hour aboard the U.S.S. Enterprise at different times may equal as little as three Earth hours. The star dates specified in the log entry must be computed against the speed of the vessel, the space warp, and its position within our galaxy, in order to give a meaningful reading." Therefore star date would be one thing at one point in the galaxy and something else again at another point in the galaxy."

"I'm not quite sure what I meant by that explanation, but a lot of people have indicated it makes sense. If so, I've been lucky again, and I'd just as soon forget the whole thing before I'm asked any further questions about it."

Star Trek 30 Years Special Collector's Edition 
Star Trek 30 Years Special Collector's Edition, published in 1996 by Paramount Pictures, states on page 81:

"Few Star Trek topics generate as much heated debate as the stardate system, the time calculation used by the United Federation of Planets which was introduced to the classic series by Gene Roddenberry, who borrowed the notion from the Julian date currently used by astronomers. Developed by Joseph Justus Scaliger (who named his dating system after his father, Julius Caesar Saliger), the Julian time calculation measures the number of days elapsed since 1 Jan. 4713 BC, the date derived by Joseph Justus. In the case of the 30th anniversary of the air date for the original series (8 Sept. 1996), that's 2,450,335 days. To make it easier, astronomers only use the last five digits – making 50335 the Julian date for the Star Trek anniversary. For Star Trek, Roddenberry added a single digit after the decimal point (50335.2) to represent one of the 10 time measurements in a 24-hour period... Roddenberry borrowed the five-digit Julian date, shortening it to four digits and renaming it "stardate"."

The Next Generation era 

For the series that would come to be known as Star Trek: The Next Generation, Gene Roddenberry was intent on demystifying stardates, joking in his notes of May 14, 1986 that "In the original series, Stardates were determined by a complex formula based on the distance from Earth multiplied by the Producer’s birthday." The revised scheme would simply be a calendar date formatted YYY.MMDD, with the first season set in the year (2)487, the second in (2)488 and so forth, five hundred years into the future. To preserve order, the recommended day and the month would be the date of script assignment, to be replaced in the end by the date of shooting. (In a likely refinement, a typical summer-to-spring sequence of production dates would’ve required seasons to straddle two calendar years: 2487/88, 2488/89...) Anniversaries such as that of the lunar landing on stardate 487.0720 (pronounced "487 point oh-seven twenty") could then be celebrated by the crew. 

Ultimately, however, the teleplay of  dated April 13, 1987 was assigned stardates ranging from 42353.7 to 42372.5. (Star Trek: The Next Generation Companion CD) This was changed to 41153.7-41174.2 on the air, consistent with the following description in Star Trek: The Next Generation Writer's/Director's Guide of March 23, 1987 (p. 13):

"A stardate is a five-digit number followed by a decimal point and one more digit. Example: "41254.7." The first two digits of the stardate are always "41." The 4 stands for 24th century, the 1 indicates first season. The additional three leading digits will progress unevenly during the course of the season from 000 to 999. The digit following the decimal point is generally regarded as a day counter." 

As in TOS, stardates from the first season of TNG would sometimes decrease with time. In one noticeable example Tasha Yar's death occurs around 41601.3 (), but she was alive in episodes with greater stardates such as , set around stardate 41997.7. 

The second season revision includes more detailed text regarding the decimal place, reiterating The Original Series rule:

"A Stardate is a five-digit number followed by a decimal point and one more digit. Example: "42254.7". The first two digits of the Stardate are always "42." The 4 stands for 24th Century, the 2 indicates second season. The additional three leading digits will progress unevenly during the course of the season from 000 to 999. The digit preceding the decimal point counts days, and the digit following the decimal point counts one-tenth of a day." 

By the sixth season, "consecutively" had replaced "unevenly" from the above quote, consistent with the lack of decreasing stardates in later seasons of TNG.

"A Stardate is a five-digit number followed by a decimal point and one more digit. Example: "46254.7". The first two digits of the Stardate are "46." The 4 stands for the 24th Century, the 6 indicates sixth season. The following three digits will progress consecutively during the course of the season from 000 to 999. The digit following the decimal point counts tenths of a day. Stardate 45254.4, therefore, represents the noon hour on the 254th "day" of the fifth season. Because Stardates in the 24th Century are based on a complex mathematical formula, a precise correlation to Earth-based dating systems is not possible."

In actual fact, these thousand "days" would elapse in roughly a year, as demonstrated by numerous references in dialogue to events from previous seasons. The "century" digit was clarified as early as , where the imaginary Jean-Luc Riker asks the computer to display his birthday party of stardate 58416, said to be less than sixteen years in the future of 2367. The initial digit may have been inspired by the 24th century, but in-universe it changes once a decade.

The writers of the  further developed the system by having a calendar year start at 000 and end at 999, although this does not fit all references in the show, such as a Diwali celebration around stardate 44390, too early in the year according to the simplified system. () Stardate 41986.0 was in 2364 according to , hence the simplified system assumes that stardates 41xxx.x covered the entire year 2364, stardates 42xxx.x the entire year 2365 and so forth. As stated in Star Trek Chronology (p. 95):

"The year 2323 works out as the zero point for the system of stardates developed for Star Trek: The Next Generation, assuming that the beginning of year 2364 (the first season of Star Trek: The Next Generation) was stardate 41000, and that stardates progress at 1000 units per year. In other words, under the Next Generation system of stardates, January 1, 2323 would seem to correspond to stardate 0. This probably shouldn't be taken too seriously, because Star Treks stardates have never been too internally consistent, but we're mentioning it here because it's kinda fun."

The second digit increased every season in TNG spin-offs as well. Since the contemporary DS9 premiered during the sixth season of TNG, stardates on the show ranged from 46379.1 to 52861.3. Likewise, the first season of Voyager (2371) would have paralleled the eighth season of TNG had it continued, so Voyager stardates ranged from 48315.6 to 54973.4. In at least one draft of the script,  had a stardate of 47844.9, but the initial digits were changed to '56' for the film, consistent with Riker having been Picard's "trusted right arm for fifteen years." However, stardates of events prior to , but not so far back as the time of TOS, do not always conform to this method of counting. According to the Star Trek Chronology:

"Editors' confession: In "Dark Page" (TNG), an entry in Lwaxana's journal dated stardate 30620.1 is established to be during the year in which she got married, 2328. Unfortunately, under the Star Trek: The Next Generation system of stardates (which allocates 1,000 stardate units per year, and puts the beginning of year 2364 at stardate 41000) the beginning of the year 2328 should be around stardate 5000. Star Trek technical consultant (and Chronology co-author) Mike Okuda decided that a four-digit stardate would be confusing since this sounds like an Original Series number, so he arbitrarily picked 30620, even though it is not consistent with stardates used elsewhere in the show."

Okuda noted that in the Star Trek Chronology that there were "ambiguities" inherent in stardate calculation.

In addition to the overall rate of approximately one thousand units per year, many episodes confirm the 24-hour stardate unit mentioned in the series bibles. It is especially noticeable when the time of day is shown next to a stardate fraction, as demonstrated in the table below:

Although the vast majority of stardates are given with only one digit following the decimal point, the captain's log in  is recorded with two digits (41235.25 and 41235.32) and other references have two, three, or even four digits, as in , where a stardate of 42073.1435 is seen on a viewscreen in the Observation Lounge. Commenting on the graphic, Mike Okuda explained: "I always thought that the numbers after the decimal were fractions of a 24 hour day, meaning that .1435 would be about 3:20 in the morning. Which is really early in the day for a doctor's appointment..."  In , Seven of Nine travels back in time from 52861.274 to 49123.5621. Occasionally there are no digits, such as when "today's date" is given as stardate 47988. ()

Alternate reality 
The stardate format from the latest film series is credited to screenwriters Roberto Orci and Alex Kurtzman. According to Orci, they "used the system where, for example, 2233.45 or whatever means 23rd century, 33rd year of that century, and the .45 indicates the day of the year out of 365 days."  During a Q&A session, Orci restated that a stardate is "the year, as in 2233, with the month and day expressed as a decimal point from .1 to .365 (as in the 365 days of the year)."  He posted a similar reply on Twitter: "star date=standard year, with decimal representing day of year from 1-365."  

The new stardates are similar to the s of ISO 8601, which would express the first day of 2260 as 2260-001, and the last as 2260-366. Orci hasn't clarified whether leap days increase the count to .366, which would be expected if the years are Gregorian. When asked about 2230.06 and 2233.04 from the  screenplay, with only one leading zero instead of two or none, he replied that it could have been an error.  IDW's  show the latter number as 2233.4, while  places Kirk's birthday "a couple of days" after 2263.2 from his log entry. Shortly thereafter, Ambassador Spock's date of death is displayed as 2263.02, and his date of birth again as 2230.06. When Uhura calls for help from Krall's base, her screen shows "226X.XX", which isn't labeled a stardate but does suggest an entire two-digit range. Though farther from the films' production, the  sees 2233.04 as January 4 of that year.

The alternate reality adaptation of  begins with a stardate in the new style, but the second part of that comic reverts to 1313.1, consistent with the range of its prime reality counterpart, and the same approach is taken with  reimagining, which begins on stardate 2821.5. After that story was finished, writer Mike Johnson commented at TrekMovie.com: "Speaking of typos... Going forward we are using the new Stardate system."  Even so, not every alternate stardate may have been chosen correctly for the intended chronological order. According to Johnson in the Open Channels section of "The Q Gambit, Part 4" (p. 25):

"The ongoing series is running in chronological order, except for those stories that are established as a flashback, like the origin of Science Officer 0718. So "The Q Gambit" takes place after "The Khitomer Conflict" and "Parallel Lives", and after the Enterprise has embarked on its new five-year mission after Star Trek Into Darkness."

"The Q Gambit" begins on stardate 2261.34, and yet "The Khitomer Conflict" already saw the higher stardates 2261.147, .149 and .168. "Parallel Lives" continued with .274 and .234 in that order. "Live Evil, Part 1" could not have been set after , where the Enterprise is destroyed. Still, the digits after the separator always fall within Orci's range, even if the comics do not provide the matching days of the month. The table below shows only new-style stardates from the films and other sources, along with their calculated equivalents in the Gregorian calendar. Given the above evidence, the conversion provisionally assumes that .0# was always intended to mean Day #, not a fraction of the year.

As seen in the table, when asked by the alternate , the computer aboard the  reports a manufacturing stardate of 2387, consistent with the timespan of 129 years stated earlier in the film. The comic miniseries Star Trek: Countdown, which details events in the prime reality that led to the 2009 film, nevertheless gives its latest stardate as 64467.14, resulting in mid-2387 according to the Chronology rules. Moreover, Star Trek Online, set over twenty years after the destruction of Romulus, continues to use the format created for TNG, placing it in the 86000 range; on the other hand, Star Trek: Timelines freely applies alternate reality stardates to events from the prime reality.

Star Trek: Discovery / Star Trek: Strange New Worlds 
A week before the premiere, the Star Trek Twitter page began counting up from 1200.4, continuing daily with 1201.5, 1202.4, 1203.4, 1204.5, 1205.4, 1206.5, and finally 1207.4, consistent with stardate 1207.3 of the first episode.  While this rate of increase matches the convention in TOS, the numbers are higher than 1024.7 for Joran Dax's birth in the following decade. Later episodes establish stardates in the actual TOS range, as well as the familiar changing rates and numbers decreasing with time. Having reached a peak in Season 1 of 4851.5, the initial digit reverts to 1 in Season 2, which ends with stardate 1201.7. Season 3 begins in the far future but preserves stardates as revised on TNG: 865xxx.x for the year 3188, though a number with eight integer digits and a decimal appears in an Emerald Chain document.

Star Trek: Picard 
Writer, executive producer, and first season showrunner on Star Trek: Picard, Michael Chabon, eschewed the use of stardates, stating in an Instagram story dated 26 February 2020:

"Stardates, in my view, and I know this is going to make some people mad, are a uniquely perverse form of uninformative information. Using a stardate tells you precisely nothing. Even people who know how to interpret and convert them have to go off and interpret and convert them to have them mean something. Giving an audience the stardate is like I wanted to know if I needed to put on a sweater or not, and you told me the temperature outside in Kelvin. 'It's 287 out.'"

Deviations from production norms 
Stardates would occasionally deviate from the prevailing production norm throughout Star Trek incarnations. Examples include:
 In , the stardates within the episode progress by 1.4, from 1312.4 to 1313.8, in what could not be more than a few days, yet the birthdates of Gary Mitchell and Elizabeth Dehner are given as 1087.7 (onscreen dossier age: 23) and 1089.5 (onscreen dossier age: 21), respectively. However, the numbers aren't explicitly labeled as stardates.
 The animated episode  set in 2269 has a stardate of 1254.4. This is lower than in any TOS episode, including the first Kirk-era show, , set in 2265 with a stardate of 1312.4.
 In , the opening graphic for Project Genesis is given a stardate of 7130.4, which should predate the USS Enterprise refit, yet Captain Kirk commented that the recording was just over a year old around stardate 8130.
 In , Riker dropped the fifth digit in his log, stating "stardate 4124.5". His entry is missing from the revised final draft of 10/26/87; it is surrounded by stardates 41242.4 and 41242.45, as recorded in Picard's log.
 In , set during stardate 54014.4, Tuvok mentions that his date of birth is stardate 38774, but he was born in 2264.
  gives a stardate of 54868.6, which would suggest a date sometime in late 2377, but in fact the episode is set on the 315th anniversary of the first contact with Vulcans, which works out to April 5, 2378.

Franz Joseph stardates
Aside from those patterned after TOS, the stardates in the Star Fleet Technical Manual were generated using calendar dates of the 1970s, formatted YYMM.DD. This can be inferred by comparing the dates of first printing (November 1975) and of the 20th anniversary edition (September 1986) with the corresponding stardates, 7511.01 and 8609.01, as well as the decimal digits in technical order stardates, which suggest days of months. In addition to being easy to use, such stardates had the advantage of roughly matching in-universe ranges from the original film era. The 1979 Star Trek (Stardate) Calendar also used this format.

Apocrypha

FASA reference stardates 
FASA's  released in the early 1980s used  similar to those used by Franz Joseph. However, they prefixed a digit and a slash to represent the century, starting with the year 2000, so January 1, 2000, was 0/0001.01 and the Organian Peace Treaty was signed on 2/0801.24, or , according to Star Trek Spaceflight Chronology. Preceding centuries are negative, so the first episode of TOS aired -1/6609.08.

Novels 
In the novel Where Sea Meets Sky, Captain Christopher Pike has to use conversion formulas to convert stardates to the Gregorian Calendar for his friend Nowan from the bar The Captain's Table.

In the Millennium novel The War of the Prophets, the stardate system is based on hyperdimensional distance averaging.

External links 
 
 
  – primarily develops one particular theory of stardates that has gained some currency
  – has calculations and calculators based upon information from the television series' and movies
  – database of stardates and logs from the  and television series
  – includes ordinal dates, which are practically identical to the alternate reality stardates

de:Sternzeit
es:Fecha estelar
fr:Date stellaire
it:Data stellare
ja:宇宙暦
nl:Sterrendatum
sv:Stjärndatum
Time measurements