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Last update: Feb 15 1997 Version 1.5
by Andrew Main <zefram@fysh.org>
1996-03-28, stardate [-31]7269.00



This FAQ addresses the problem of what stardates mean. Of course, considering that stardates are merely a way to refer to points in time, any meaningful answer must refer to some other standard way to refer to time. The adage about standards is especially true here -- there are so many to choose from.

Ultimately, it is desired that stardates be related to a standard currently in use. For example, Greenwich Mean Time (GMT). This is defined as local mean time at the Royal Observatory in Greenwich, London. Local mean time is defined in terms of the observed noon on each day. Consequently, each day of GMT is a slightly different length, and not even an integral number of seconds. (Otherwise, the second varies in length from day to day, which would be even worse.) This is, therefore, in its strictest form, not a very good standard.

UTC (Universal Coordinated Time) is a better standard. The second is the unit of time defined by the SI, and can be regarded as having a fixed duration. Each day is exactly 86400 seconds, except for the occasional day of 86401 seconds used to keep in line with GMT (to within one second). To date there have been thirty such leap seconds, the most recent on 1995-12-31. Theoretically there may also be days of 86399 seconds, though there have not been any so far, and it is not anticipated that any will be needed. This is a better standard for specifying time, but still suffers from variable day lengths, which makes its handling awkward.

However, both GMT and UTC suffer from a more fundamental flaw: they depend on observations made from a single planet. If the planet is changed significantly, or is destroyed, then the time standard is meaningless. Furthermore, anyone in a different reference frame (i.e., anyone not on Terra) will disagree with Terrans about the order of certain events. This is a fundamental aspect of relativity.

Fortunately, Treknology provides a solution. For FTL travel to avoid violating causality, it has to take place in such a way that all FTL travellers have the same frame of reference. (Refer to Jason Hinson's "Relativity and FTL" FAQ for the explanation of all this.) The only standard timebase that could be considered universal would be one based in this frame of reference. It has been established numerous times in ST:TNG that there is a Federation Timebase, which presumably is arranged in just this way.

Thus it is established that stardates are linked to the FTB. But what about Terran calendars? Because this standard reference frame is currently unknown to Terran science, it can be conveniently assumed to be close to the reference frame of Terra. Because the relation to Terran time is only approximate, the choice of GMT or UTC is irrelevant, and the distinction will be ignored from here on.

This makes it possible to refer to points in time -- unambiguously -- using the Gregorian calendar, which is what will be done for the remainder of this FAQ. The Gregorian calendar is chosen because it is the most widely used on Terra. Furthermore, it will be assumed that every day is exactly 86400 seconds long.


Since there must be some basis for a system, the following will be assumed, in decreasing order of importance:

  1. Nothing will be arbitrary, unless it is unavoidable. The idea is that anyone working from the same data, using the same principles, will come to the same conclusion.
  2. Stardates occur in the `right' order. That is, the stardate will always increase numerically in the direction of advancing time. From time to time it will be necessary for the stardate to be reset to zero, but only on a finite set of occasions. On the principle that the system be as simple as possible, this set should be as small as possible.
  3. Stardates will, in general, increase at a constant rate relative to the Federation Timebase. From time to time this rate may vary, but only on a finite set of occasions. On the principle that the system be as simple as possible, this set should be as small as possible.
  4. Stardate rates will be round numbers relative to Terran phenomena such as days or years.
Given the above assumptions -- and working by the principle that the system should be as simple as possible -- what follows is the investigation of the stardate system. ST:TOS stardates will be discussed first; the ST:TNG stardates can be added to the system later (and relatively easily). Note: unless otherwise stated, all stardates specified are exact. As discussed in the previous section, Terran times given are necessarily approximate.

The system worked out below does not attempt to explain known writing errors. Just as Data's remark in "Encounter at Farpoint" ("Starfleet class of '78...") is commonly ignored, errors of stardate such as those in "Dark Page" are ignored here. Verbal bloopers are also ignored, naturally. Also, because of their irreconcilable inconsistency, stardates other than the main one for each episode must be ignored.


Going by the Star Trek Chronology, the first and last episodes are "The Corbomite Maneuver" (SD 1512.2; assumed to take place 300 years after it aired in September 2266) and "Turnabout Intruder" (SD 5928.5; early 2269).

This choice of episodes has some faults. "Turnabout Intruder" was the last episode aired, but the stardate of "All Our Yesterdays" was later (stardate 5943.7 against 5928.5). Under the principle that stardates occur in the right order, "All Our Yesterdays" must be taken as the end-point for the mission. (It makes little difference anyway, because the actual date is only conjecture.)

Similarly, there is room for dispute over which episode comes first. "The Corbomite Maneuver" (SD 1512.2) was first in regular production, but that doesn't necessarily mean anything. Similarly, "The Man Trap" (SD 1513.1), the first episode aired, is not a good starting point. "Where No Man Has Gone Before" (SD 1312.4) was first overall in both production and stardate, but is generally regarded as being quite distinct from the rest of the series. "Mudd's Women" (SD 1329.1) has the earliest stardate of the episodes in regular production, providing another possible starting point. However, the episode "Charlie X" (SD 1533.6) contains a clear reference to Terran dates, making all this arbitrariness unnecessary.

[Note: the Chronology lists the stardate of "The Man Trap" as 1513.1, but the Star Trek Compendium says 1531.1. I would appreciate it if someone could check with the episode itself, to confirm one date or the other.]

At one point in "Charlie X", Kirk states that it is Thanksgiving day on Earth. For those not familiar with American customs, Thanksgiving day is the fourth Thursday in November. Assuming Kirk was indeed referring to that same Thanksgiving day (which seems likely), and accepting the Chronology's calculation of year, this pins down the date of Kirk's statement to 2266-11-22. Let this be the day after the initial statement of the stardate for the episode, and the conclusion is reached that the episode started on 2266-11-21. This is only two months different from the Chronology's conjecture, and has the advantage of being almost completely non-arbitrary.


Stardate 1533.6 was sometime during 2266-11-21. According to the Chronology, the end of the series (SD 5943.7) was in early 2269. The is approximately 4400 units spanning two and a half years. A nice round number close to this rate is 5 units per day. (4.8 units/day -- 0.2u/hour -- is also within the possible range. It would be less plausible, however, because it relates to hours, which are purely a human invention, whereas days are a natural phenomenon.)

With this rate, to make things easier, it can be assumed that any exact multiple of 5 units is midnight. So the Thanksgiving day in question, 2266-11-22, runs from exactly SD 1535 to just before SD 1540. Therefore, SD 5940 is 00:00 on 2269-04-21 ("All Our Yesterdays" is on that day).

This rate puts "Where No Man Has Gone Before" in 2266, in contradiction to the speculative date in the Chronology. (This is not a problem, because there is no stronger evidence to back up that particular speculation.) It also set dates for a number of other events that the Chronology has assigned conjectural dates. It gives us a date of 2270-02-09 for ST:TMP, which is not acceptable. ST:TMP should occur in late 2271, to give Kirk time to have "not logged a single star hour in two and a half years". So the stardate rate must have changed at some stardate between 5943.7 and 7411.4.


Going by the Star Trek Chronology again, these dates may be useful. "Star Trek: The Motion Picture" (SD 7411.4) was in late 2271, at least 30 months after the end of the original TV series. "Star Trek III: The Search For Spock" (SD 8210.3) was in late 2285. "Star Trek VI: The Undiscovered Country" (SD 9521.6) was in 2293. These dates are conjectural, but they have a solid basis. They may be moved a little without contradicting anything other than the Chronology itself.

(By the way, ST:TMP really does have a stardate of 7411.4, despite the manuals that say 7412.6. One of the barely-audible messages at the Epsilon 9 station mentions a rendezvous between two Federation ships to take place on stardate 7411.4. If you listen carefully it is also possible to make out the ships' names and registry numbers -- scout Columbia NCC-621 and scout Revere NCC-595. These names and numbers match those in the list of scouts in the "Star Fleet Technical Manual".)

TVH:STIV is about 3 months after STIII:TSFS according to Captain Kirk's log, but this reference can be ignored because he may have meant Vulcan months.


It turns out that the stardate rate has to change sometime between ST:TMP and STII:TWOK, as well as sometime before ST:TMP. The details of that period, encompassing ST:TMP, can't be calculated until this bit, for the remainder of the classic films, has been done.

The reference points to use for this are STIII:TSFS (SD 8210.3; late 2285) and STVI:TUC (SD 9521.6; conjectured to be 2293). The gap is 1311.3 units, covering 7-8 years. A suitable rate is 0.5 units per day. (0.48u/d -- 0.02u/hour -- is also within the possible range.)

Similarly to the first period of stardates, it can be assumed that any exact multiple of 0.5 units is midnight. This means that the days on which STIII:TSFS and STVI:TUC start will start at stardates 8210.0 and 9521.5 respectively. The calculation of exactly which dates these are must wait until the details of the intermediate stardate rate have been calculated.


Neither of the periods of stardates discussed above gives a satisfactory date for ST:TMP. It is therefore necessary to have an intermediate period of stardates to link the two. It is possible to make this link with a single intermediate period. This period must use up stardates much more slowly than either of the adjacent periods.

This intermediate period can have a rate of about 0.156u/d at the most. To have a rate any higher, this period would have to extend into ST:TOS or beyond STII:TWOK. It would be possible to use a rate of 0.15u/d (which has the advantage of making a standard 8-hour shift exactly 0.05 units long), but this makes the day length messy. (3u/d or 0.3u/d would be more manageable, but it isn't possible in this case.) The most logical rate to use is 0.1u/d.

Now to place ST:TMP... It must be a fair bit more than 30 months after "All Our Yesterdays", ideally in late 2271. To make the changeover point from ST:TOS stardates to this period an exact midnight -- it would be madness to do otherwise -- it must be a multiple of 5 units. This means that moving it one day forward or back changes the date of ST:TMP by 49 days, because the stardate rates differ by a factor of 50. The most reasonable date possible for ST:TMP under this limitation is 2272-01-10, with the changeover at SD 7340.0 (2270-01-26). This is not quite in 2271, but close enough not to cause problems with later dates.

And for the second changeover... It turns out that fairly sensible dates for STIII:TSFS and STVI:TUC can be obtained by putting the second changeover at SD 7840.0 (2283-10-05) -- exactly 5000 days (500 units) after the first changeover. This makes it all look designed. This puts STIII:TSFS at 2285-10-14, consistent with the Chronology. It also makes STVI:TUC 2292-12-19, which is not quite the conjectural 2293, but is close enough.


Throughout ST:TNG stardates have increased at approximately 1000 units per year. (In fact, during ST:TNG, the second digit of the stardate indicated the season.) From these facts, the Chronology has conjectured that ST:TNG stardates increase at exactly 1000 units per year. Numerous references within the series supports this conjecture. Of course, they support it because the shows were written with that system in mind. It would be difficult to contradict this.

However, there are a few inconsistencies in this respect within the series. In "Eye of the Beholder" (ST:TNG, SD 47622.1; incidentally, this is the second of (so far) three very near title clashes in Star Trek -- there was an animated Star Trek episode called "The Eye of the Beholder") an incident at Utopia Planitia is referred to both as stardate 40987 and as eight years ago; allowing for rounding, this gives a year length of between 704.4 and 954.4 units. In "The Pegasus" (ST:TNG, SD 47457.1), the disappearance of the Pegasus was stardate 36764 and twelve years ago; this gives a range of 807.8 to 974.4 units per year. In "Second Sight" (ST:DS9, 47329.4), the battle of Wolf 359 (SD approximately 44002) was exactly four years ago, giving a year length of 832 to 834.75 units.

There are some other references consistent with an 833 unit year, but most are not so clearly referring to Terran years. In any case, the vast majority of references support 1000 units per year, leaving these other references as isolated mistakes.

In "The Neutral Zone" (SD 41986.0), Data stated that the year was 2364. This almost solves the problem of year calculations. The only problem is that Data did not go on to say exactly what day of the year it was, so there is an uncertainty of one year when calculating dates from this.


Note that ST:TNG stardates have five digits before the decimal point, where ST:TOS stardates have four. This would seem to suggest a change of outlook on the part of the Federation, from short-term to long-term. This coincides with the change from stardate units being convenient fractions of Terran days to being a convenient fraction of a year. Also, the length of stardates in ST:TOS could allow for up to about 5.4 years before needing to be reset to zero, whereas the ST:TNG stardates only need to be reset once a century. (Presumably one often needed to specify which period of 5.4 years one meant by a particular stardate.)

The Chronology proceeds under the assumption that all first season stardates were in the year 2364, and then all second season in 2365, and so on. There isn't really any evidence to support this, but it makes things neat. The production crew have occasionally calculated exact dates on this basis. In order to keep things simple, it will be assumed that this is how the stardates actually work. This makes stardate 00000.0 midnight at the beginning of 2323-01-01.

Stardate 99999.9 should be about 50 minutes before midnight on 2422-12-31, after which the stardates get reset to zero again. However, it is not possible to state this as being exact, because not all centuries are the same length. Every fourth century contains 25 leap years; the rest have 24 each. The difference in the lengths of individual years creates a more immediate problem: the 1000s of units can't match up exactly with calendar years.

Obviously, one solution would be for the stardate rate to vary from year to year, making each year 1000 units whether it is 365 or 366 days long. This is not acceptable as a universal time system, however. The rate changing every fourth Terran year makes things difficult for the Vulcans, and the Andorains, and in fact almost every member of the Federation.

So the rate must make 1000 units fit a mean solar year of 365.2425 days exactly. (Actually that's not quite exact, but that is the exact mean length of a year by the Gregorian calendar. This is more appropriate, because the Gregorian calendar is being used to specify dates.) 400 years is exactly 146097 days, no matter which 400 years one counts. By a happy coincidence, this is exactly 20871 weeks. (This fact is of no practical use, except in the construction of perpetual calendars.)

For convenience, it can be conjectured that starships on extended voyages -- and maybe some civilians too -- use a standard year of length 365.2425 days. This doesn't mean they add on an extra 5.82 hours at the end of the year, but that they distribute it evenly throughout the year. This makes each day about 57.4 seconds longer than 24 hours. In fact, to make chronometers visually indistinguishable from those previously in use, the second would get longer.

This standard year is exactly 31556952 SI seconds long, but is internally divided into the usual 31536000 seconds. This makes the `chronological second' approximately 1.00066 SI seconds, and even Data would have difficulty distinguishing the two.

The two calendar styles could coexist quite easily, because they would rarely be more than a few hours different. In order for them to coexist over a long period of time, they must agree on what day of the week any particular date falls on. (A consequence of this is that existing perpetual calendars will still be applicable to the new calendar.) Where there would be a leap day in the old-style Gregorian calendar, there is merely a jump in the day of the week. For example, Wednesday 2396-02-28 would be followed by Friday 2396-03-01, missing out Thursday 2396-02-29 which would appear in the Gregorian calendar.

This new calendar will hereafter be called the "quad-cent calendar". It comes exactly into line with the old-style calendar every 400 years. Since the origin for ST:TNG stardates is 2323-01-01, that must be when the two calendars match up. (The next time will be 2723-01-01.) Hereafter, quad-cent calendar dates will be written like 2323*01*01, instead of 2323-01-01.


SD 9521.5 corresponds to the date 2292-12-19. The digits run out and are reset to zero on 2295-08-03. This starts a special `issue' of stardates, whose sole purpose is to bridge the gap to 2323-01-01, when the new-style stardates take over. In this new issue, SD 5000.0 is 2322-12-20, almost exactly 30 years after STVI:TUC. This makes 2323-01-01 SD 5006.0. So stardate 5006.0 in that issue became stardate 00000.0, and the date, 2323-01-01, became 2323*01*01 for the purposes of stardates.

If Thanksgiving were twelve days later, these numbers would be unbelievably neat. So neat, in fact, that one might well reach the conclusion that this system was actually designed to work this way.


From the ST:TOS stardates we know that SD 1530 is 2266-11-21. Extending this back, SD 0000 is 2266-01-19, well after the beginning of the five-year mission. To go further back, we must go into an earlier issue of stardates. In this earlier issue, SD 9995 must be 2266-01-18 (one day before the ST:TOS stardate 0000). This makes SD 0000 in this issue 2260-07-29. Continuing this process backward, it should be possible to find a sensible starting point for all stardates.

The theory is here supported by the ST:DS9 episode "Equilibrium", which puts Joran Bella's birthdate at stardate 0024.7, and notes that this is in 2260. (This theory makes it 2260-08-02.) However, the same episode puts his death as stardate 8615.2 and 2286. This is not quite consistent with this theory, being two years out.

None of the major real-life space events is a 0000. The 43rd issue before the classic series has its 0000 on 2030-08-04, and 2030 is supposed to be the year of Zefram Cochrane's birth; this is a rather implausible candidate for the origin. The 37th issue before the classic series has its 0000 on 2063-06-12, just a couple of months after Cochrane's first demonstration of warp drive (2063-04-05, according to ST:FC). I think the powers that be here missed a great opportunity here. It looks like stardates just aren't based on any significant event in space travel.

The 19th issue before the ST:TOS stardates has its SD 0000 on 2162-01-04, which is tantalisingly close to 2161 (Federation incorporation). Taking this as the origin of stardates, it could mean that Starfleet originally used old-style Terran dates, but found them inappropriate for deep-space use. A few months after incorporation, then, they started up stardates.

If we call these first stardates `zeroth-issue', which will be written like [0]0000, ST:TOS uses 19th-issue stardates (e.g., [19]1530 is 2266-11-21). The partial issue to link the TCFS stardates with the ST:TNG stardates is the 20th issue, and ST:TNG stardates are 21st issue. This notation provides a convenient way to refer to stardates a long way from the current time.

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