My Vulcan Calendar

The Year

The biggest problem with trying to turn the various facts available into a working calendar is the choice of a home system for the Vulcans. 40 Eridani is one of the more likely stars nearby (relatively speaking) that could harbour a planet like Earth. There’s nothing wrong with the choice on that score. Unfortunately, like most of the “nearby” (we have to speak relatively here; the stars are all a very, very long way away in our terms) stars, 40 Eridani A is smaller than our Sun. I go into more detail in Building Vulcan, but with a smaller sun, there has to be a shorter year. Luckily, this shorter year turns out to be a little over six months long. If Vulcans measure time in units of two orbits of Vulcan around 40 Eridani A, then it becomes possible for their time units to be longer than an Earth year. How long, though?

The only evidence available is the pon farr cycle. As explained in Pon farr, it’s something that happens to Vulcans, on average, every seven Earth years. What happens if we assume that some multiple of Vulcan years is exactly equal to seven Earth years? I readily accept that it’s unlikely, but it is the only real clue there is, and if it works, then it must at the very least be a good approximation. After all, I’m making things up just as much if I set the interval at 6.97, 7.01 or some other arbitrary “close match” as if I set it at exactly 7.

At this point, I need to pick a name. If a Vulcan “year” isn’t a year, what am I going to call it? “Time measuring unit” is clunky, and could refer to anything. “Cycle” is shorter, but equally uninformative. When I started to consider “bicycle” because it was a unit of two orbits, I realised that I needed to go in a completely different direction. Although they don’t represent “years” in precisely the same way, what names have been suggested for the Vulcan equivalent of a year? “The Vulcan Language” by Mark R. Gardner (the print version of the Vulcan Language Institute website) suggests tevun. It’s a perfectly acceptable word, but I took the names of the Vulcan months from a completely different source. For the sake of consistency, I’ve adopted the word for “year” proposed by the version of the Vulcan language developed by Marketa Zvelebil: r’tas. After a lot of investigation, I’ve concluded that the plural of r’tas is r’tas.

So how many Vulcan r’tas will be the equivalent of seven years? We can rule out larger numbers, since the evidence says they’re likely to be longer than Earth years. An exact match can be discarded on the same grounds. What about six r’tas? That makes one r’tas 1.17 Earth years long. Before going any further, let’s see how that works, using my suggested dates.
Tuvok Spock T’Pol
Born September 2262 January 2230 August 2087
Seventh Birthday November 2270 March 2238 October 2095
Eighth Birthday January 2272 May 2239 December 2096
57th Birthday March 2329 July 2296 February 2154
98th Birthday January 2377 May 2344 December 2201

Tuvok’s birth is a little early, since I calculated it from a stardate, but his 98th birthday is at a reasonable time for VOY “Fury.” Likewise, if Spock is born sometime in January 2230, as suggested by a deleted scene in the 2009 “Star Trek” film, then TAS “Yesteryear” must happen 30 years after he was seven Vulcan years r’tas old, in other words, sometime between March 2268 and May 2269. It’s the scientists studying the Guardian who say they were looking at events “25 to 30 Vulcan years ago.” Since they’re not Vulcan, the inaccuracy is forgiveable, I hope. Spock himself only refers to “30 years,” without specifying “Earth” or “Vulcan.” For my purposes (and on the basis of my arguments so far) he’s talking specifically about Earth years. 30 years is equivalent to 25.71 r’tas, so the various figures do tally. T’Pol gives only one suggestion as to her age. In ENT “Zero Hour,” she says she’ll be 66 years old on her next birthday. To be consistent, that means 66 Earth years. Of course, if she’d said 63 or 70, then the number would translate to an exact number of r’tas. As it is, 66 years is equal to 56.57 r’tas. Vulcans are pretty good at sums, so it’s possible that she’s converted everything to the Earth equivalent. By that argument, she’d be born exactly 66 years before her “Earth birthday.” If we assume that her next birthday is quite soon, since she brings up the subject, then because I’ve placed ENT “Zero Hour” in February 2354, March 2088 would be her birthday, around T’lakht, 8748 V.E. If she uses her Vulcan birthday, but converts her age to Earth years, then she will have to be 57 r’tas old in (for the sake of argument) March 2154. That makes her 66.5 years old, so she’d be rounding down. That quite appeals to me, so I’ve made her 57th birthday in re’T’Khutai 8805 V.E., putting her birth in re’T’Khutai 8748 V.E., or August 2087. For the sake of completeness, assuming she’s 66 r’tas old in 2154, then she’d have been born in re’T’Khutai 8739 V.E., or February 2077. That’s quite considerably earlier than any other estimate, and I don’t think it fits either the general consensus, or my own interpretation of the evidence. The practicality of selecting this value for two orbits of Vulcan around 40 Eridani A will be explored in Building Vulcan.

The Day

Selecting a value for the Vulcan day is also quite arbitrary. Although an ingenious attempt to “reason backwards” from Sarek giving his age as 101.437 Earth years in TOS “Journey to Babel” was made by Kenneth Reeler in “The Best of Trek” (unnumbered, but #17, published 1994), I found the arguments too convoluted to be really convincing, and if you’ve made it this far, you’ll know that’s certainly going some! Rather than just plucking a number from thin air, I decided to examine the evidence, what there is of it. “Star Trek” visits Vulcan several times, and looking at the internal chronologies of stories set on that planet, it’s very difficult to see that a Vulcan day differs massively from the length of a day on Earth. Certainly, if the day were hugely shorter or longer, it seems odd that it’s not mentioned. Certainly the (in my version “apocryphal”) events of TAS “Yesteryear” strongly imply that the days are of a similar length. For that reason, I decided to take the day listed in “U.S.S. Enterprise Officer’s Manual”, since it was written by Geoffrey Mandel, who also produced the “Star Trek Star Charts” and the earlier “Star Trek Maps”. If there’s anyone who gets to say how long the days are on Vulcan, I think it’s him. So, a Vulcan day lasts 26 hours, 43 minutes and 7 seconds. Now we know that an r’tas lasts 382.76 Vulcan days. As the brief summary of the calendar shows, I’ve “tweaked” that number to 383.167, so that the calendar works without being too complicated. By adding a day in every 6th r’tas, I can divide the year into 11 Vulcan “months” of 32 days, and 1 “month” of 31 days, with the months all of equal length in a “leap year” r’tas. The “month” is just a convenient way of dividing the year, since as Spock says in TOS “The Man Trap” “Vulcan has no moon.”

I’ve named the months, as I mentioned above, by following Christopher L. Bennett’s website in adopting Marketa Zvelebil’s Vulcan names. I have the same number of months (although they’re a completely different length) and some of the names have previously been used in the “Star Trek” tie-in novels, although if they fit in with my suggestions it’ll be nothing short of a miracle. As mentioned on the Klingon Calendar page, Mr. Bennett’s “Star Trek” calendars page is at and Marketa Zvelebil’s Vulcan calendar can be found at Neither of them endorses my version of the Vulcan calendar, and I’d be surprised if they even know about it.

What Would Vulcan Be Like?

Having made all these assumptions about the Vulcan calendar, how would the information fit with what we know about 40 Eridani to make a scientifically plausible planet Vulcan? Again, to keep the length of the webpages under some sort of control, I’ve started a new page: Building Vulcan.

But First, Some Acknowledgements, and a Warning

What follows is not the responsibility of anyone except myself. If I’ve managed to get anything right, and used the correct sums, it is in large part owed to Jon F. Zeigler and James L. Cambias’ “GURPS Fourth Edition: Space”, published by Steve Jackson Games in 2006. The screencaps I’ve used to illustrate my ideas are from TrekCore, but remain the copyrighted property of CBS Entertainment. I’m using them without permission, on a strictly non-commercial basis. The various images based on them, and using other manipulated images, that I’ve made, are also not intended to infringe the rights of the original creators, and again my use of them does not imply that they are not copyrighted, or can be used freely. Although I make no claims over my images, others might, so if you want to reproduce them, it’s at your own risk.

The idea of trying to work out a Vulcan calendar, and apply it to what we know about the 40 Eridani system, comes from a Trek BBS thread, “Vulcan years vs. Earth years” started by, as far back as 2011. I have to acknowledge that T’Girl suggested that “Delta Vega” was Vulcan’s mysterious “thing that isn’t a moon,” an idea that I only came to accept very gradually. And that a lot of my comments in that thread were based on second-hand sources that didn’t stand up at all when I started looking into this more carefully.

Vulcan Calendar
Building Vulcan

by StrauchiusStrauchius on 14 Dec 2014 17:04, last updated on 09 Mar 2016 16:19