# Julian date Vs. star date **URL:** \ **Category:** Factual Questions\ **Created:** [August 22, 2002, 7:09am UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046 "2002-08-22T07:09:49Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![the\_duke\_69](https://avatars.discourse-cdn.com/v4/letter/t/48db29/32.png) [@the\_duke\_69](https://boards.straightdope.com/u/the_duke_69)\ **Post date:** [August 22, 2002, 7:09am UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/1 "2002-08-22T07:09:49Z")
what is the diffrence if any in the two? what is the julian date? what is star date(off of startrek)? some one told me they were they same thing. any answers would be helpfull thank you ahead of time! ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [August 22, 2002, 7:32am UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/2 "2002-08-22T07:32:05Z")
Stardates are a fictional date-keeping mechanism that has never been officially defined. No way to convert from Stardates to any other date system exists. Julian dates (abbreviated JD) are simply a continuous count of days and fractions since noon Universal Time on January 1, 4713 BCE (on the Julian calendar). (BCE means Before Common Era and is a culture-independent way of saying BC, or Before Christ.) Astronomers use Julian dates because they are an efficient way of determining how much time passes between any two dates: Simply subtract, no conversions of any type needed. The Julian date system starts far enough back that any date in recorded human history is represented by a positive number. [There are numerous online converters to translate from JD to our common calendar. Here’s one.](http://aa.usno.navy.mil/data/docs/JulianDate.html) [Fourmilab’s invaluable universal calendar converter. This one has them all.](http://aa.usno.navy.mil/data/docs/JulianDate.html) ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [August 22, 2002, 1:39pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/3 "2002-08-22T13:39:18Z")
Star dates have two purposes, one for Starfleet, and the other for The Producers. The purpose for Starfleet (I forget where I read this, perhaps “The MAking of Star Trek”) is to provide a consistent and steady measurement of the time flow unaffected by faster-than-light travel. Occasional episodes have referred to checking the current dates by referring to a nearby “time buoy”. For the Producers, it was a way to coordinate the sequence of varied episodes and events without tying it down to a specific century or year. This was very true for the original series, and became less true for the later ones, but even so, please note the following: Star Dates were four digits in the original series, and five digits after that. The first two of the 5 digit can tell you which season the episode took place in: 41xxx - Next Generation season 1 42xxx - Next Generation season 2 43xxx - Next Generation season 3 44xxx - Next Generation season 4 45xxx - Next Generation season 5 46xxx - Next Generation season 6, Deep Space 9 season 1 47xxx - Next Generation season 7, Deep Space 9 season 2 48xxx - Deep Space 9 season 3, Voyager season 1 49xxx - Deep Space 9 season 4, Voyager season 2 50xxx - Deep Space 9 season 5, Voyager season 3 51xxx - Deep Space 9 season 6, Voyager season 4 52xxx - Deep Space 9 season 7, Voyager season 5 53xxx - Voyager season 6 54xxx - Voyager season 7 There might be exceptions, but I think the above is accurate. Bottom line: One year is a thousand stardates? Can’t be, else the original series was only 37 years before Next Generation. So just forget the whole thing, okay?? ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 22, 2002, 2:27pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/4 "2002-08-22T14:27:50Z")
I’m puzzled by the idea that the Julian calandar provides an accurate count of days back to 4713 BCE. The traditional date for the founding of Rome is 753 BCE. Even if that date is likely later than the actual founding, it’s doubtful that Rome existed much before somewhere around 1000-1200 BCE. So where do they get this date of 4713 BCE? Were even the Egyptians or Sumerians in business that far back? Also, in relying on the Julian date, how do they deal with the variations in the length of the year that were sometimes introduced for political purposes during the Roman Republic, and with the extra-long year (over 400 days) at the time that Julius Caesar reformed the calendar? See [Suetonius’s](http://www.fordham.edu/halsall/ancient/suetonius-julius.html) biography of Julius Caesar: > [@](#): > > Then turning his attention to the reorganisation of the state, he reformed the calendar, **which the negligence of the pontiffs had long since so disordered, through their privilege of adding months or days at pleasure,** that the harvest festivals did not come in summer nor those of the vintage in the autumn; and he adjusted the year to the sun’s course by making it consist of three hundred and sixty-five days, abolishing the intercalary month, and adding one day every fourth year [the year had previously consisted of 355 days, and the deficiency of about eleven days was made up by inserting an intercalary month of twenty-two or twenty-three days after February]. Furthermore, that the correct reckoning of seasons might begin with the next Kalends of January, he inserted two other months between those of November and December; hence **the year in which these arrangements were made was one of fifteen months,** including the intercalary month, which belonged to that year according to the former custom. In light of all those variations, how can they be sure that they have in fact an exact count of days covering nearly 7 millenia? ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 22, 2002, 2:32pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/5 "2002-08-22T14:32:27Z")
> [@](#): > > \*Originally posted by Keeve \* > **Star dates have two purposes, one for Starfleet, and the other for The Producers.** What do Nathan Lane and Matthew Broderick have to do with Star Dates? 😛 In all seriousness, the Master has spoken on the topic: [In “Star Trek,” what exactly are “star dates”?](http://www.straightdope.com/classics/a3_367.html) ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 22, 2002, 2:51pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/6 "2002-08-22T14:51:45Z")
Actually, even though Julian Dates (JD) and stardates have nothing to do with each other, they are similar in that they’re basically a sequential counting of days (except for the 1000 days per year thing - haven’t worked that out yet). If stardates were real, the formula to convert between them would be something easy like this: JD = Stardate + 2600000 **Northern Piper** , JD keeps track of days back to 4713 BC _in the Julian Calendar_. That date (4713 BC) is just what you get if you count backward. Nobody is claiming anything like, “If you asked the current head of state to make one tickmark every year since the Julian Date began, the current total would be 6715.” The real reason that the date is set so far back is one of practicality - so that astronomers would never, ever have to use a negative number. In practice, nobody cares how many days Caesar said were in the year 92 BC or anything, because the days have been more or less constant, and a running tally of _days_, rather than year, month, day, would be accurate. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 22, 2002, 3:00pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/7 "2002-08-22T15:00:04Z")
So why do they call it the Julian date, if it’s not tied to the Julian calendar? It’s just a running total of days - why the link to the Julian calendar in the name? ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 22, 2002, 3:04pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/8 "2002-08-22T15:04:57Z")
Good question. I had to look up [the answer](http://scienceworld.wolfram.com/astronomy/JulianDate.html) myself: > [@](#): > > The number of days since noon on January 1, -4712, i.e., January 1, 4713 [BC](http://scienceworld.wolfram.com/astronomy/BC.html) (Seidelmann 1992). It was proposed by J. J. [Scaliger](http://scienceworld.wolfram.com/biography/Scaliger.html) in 1583, so the name for this system derived from Julius [Scaliger](http://scienceworld.wolfram.com/biography/Scaliger.html), not Julius Caesar. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [August 22, 2002, 3:12pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/9 "2002-08-22T15:12:40Z")
He named it after his dad. ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [August 22, 2002, 3:26pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/10 "2002-08-22T15:26:34Z")
Anyone know offhand what led to the selection of 4713 BC as opposed to 4693 BC or 4901 BC etc? Was this Helen of Troy’s birth date or something? ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [August 22, 2002, 3:59pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/11 "2002-08-22T15:59:23Z")
> [@](#): > > \*Originally posted by AHunter3 \* > \*\*Anyone know offhand what led to the selection of 4713 BC as opposed to 4693 BC or 4901 BC etc? Was this Helen of Troy’s birth date or something? \*\* He calculated it as a point where 3 major calendrical cycles coincided. The 3 cycles form a combined period of 7980 years. See [http://serendipity.magnet.ch/hermetic/cal\_stud/jdn.htm](http://serendipity.magnet.ch/hermetic/cal_stud/jdn.htm) > [@](#): > > The length of 7,980 years was chosen as the product of 28 times 19 times 15; these, respectively, are the numbers of years in the so-called solar cycle of the Julian calendar in which dates recur on the same days of the week; the lunar or Metonic cycle, after which the phases of the Moon recur on a particular day in the solar year, or year of the seasons; and the cycle of indiction, originally a schedule of periodic taxes or government requisitions in ancient Rome Meyer is, in turn, quoting Encyclopedia Brittanica at that point. There is also dispute concerning the oft-repeated story that he named it for his father: > [@](#): > > According to some accounts Scaliger named his Julian period after his father, Julius Scaliger. However in his De Emandatione Temporum (Geneva, 1629) Scaliger says: “Julianam vocauimus, quia ad annum Julianum accommodata …” (translated by R. L. Reese et al. (3) as “We have termed it Julian because it fits the Julian year …”). I tend to trust Meyer, one of the leading calendar freaks. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [August 22, 2002, 4:07pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/12 "2002-08-22T16:07:03Z")
> [@](#): > > \*Originally posted by AHunter3 \* > \*\*Anyone know offhand what led to the selection of 4713 BC as opposed to 4693 BC or 4901 BC etc? Was this Helen of Troy’s birth date or something? \*\* He calculated it as a point where 3 major calendrical cycles coincided. The 3 cycles form a combined period of 7980 years. See [http://serendipity.magnet.ch/hermetic/cal\_stud/jdn.htm](http://serendipity.magnet.ch/hermetic/cal_stud/jdn.htm) > [@](#): > > The length of 7,980 years was chosen as the product of 28 times 19 times 15; these, respectively, are the numbers of years in the so-called solar cycle of the Julian calendar in which dates recur on the same days of the week; the lunar or Metonic cycle, after which the phases of the Moon recur on a particular day in the solar year, or year of the seasons; and the cycle of indiction, originally a schedule of periodic taxes or government requisitions in ancient Rome Meyer is, in turn, quoting Encyclopedia Brittanica at that point. There is also dispute concerning the oft-repeated story that he named it for his father: > [@](#): > > According to some accounts Scaliger named his Julian period after his father, Julius Scaliger. However in his De Emandatione Temporum (Geneva, 1629) Scaliger says: “Julianam vocauimus, quia ad annum Julianum accommodata …” (translated by R. L. Reese et al. (3) as “We have termed it Julian because it fits the Julian year …”). I tend to trust Meyer, one of the leading calendar freaks. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [August 22, 2002, 4:38pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/13 "2002-08-22T16:38:56Z")
Aha! Even if Scaliger didn’t name it after his dad, he introduced it in [1583](http://scienceworld.wolfram.com/astronomy/JulianDate.html), just one year after the introduction of the [Gregorian calendar](http://scienceworld.wolfram.com/astronomy/GregorianCalendar.html), which came into force in Roman Catholic countries October 4/15, 1582. I would presume he would have been working on his project from quite some time, using the Julian calendar, and didn’t see any need to change his method of calculation. ---
**Author:** ![PolskiKing](https://avatars.discourse-cdn.com/v4/letter/p/a5b964/32.png) [@PolskiKing](https://boards.straightdope.com/u/PolskiKing)\ **Post date:** [August 22, 2002, 4:57pm UTC](https://boards.straightdope.com/t/julian-date-vs-star-date/125046/14 "2002-08-22T16:57:45Z")
What keeve stated above about stardates is mostly right, but in mind the XX and the five digits after were slightly randomized. In fact, in the begining episodes they accidently used the same stardate twice, so after that the producers kept a written record of all the used stardates. -PK