What is a "Year" According to Starfleet?

Question

We've all heard about the famous "five year mission" to explore strange new worlds and so on. And this question is asked with the thought that there might be issues with time dilation in warp drive or at high impulse speeds.

In chat, we were discussing this and one point came up: It's likely a "5 year mission" was based on 5 years according to Starfleet time. But every planet has a different year, different days, and months are basically culturally defined (if they're defined at all in some cultures).

So what is a Starfleet year? Is it an Earth standard year? An Earth leap year? A Vulcan year? When someone in Starfleet talks about a day or year, what is the basis for that measurement of elapsed time?

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Note: I am not referring to dealing with issues of time dilation. I mean what constitutes a year according to Starfleet? Is it the time it takes Earth to complete an orbit around Sol? Is it an average between Earth's year and Vulcan's year? How long is a standard year in Starfleet, assuming no time dilation? If I am on a planet and won't be leaving it and start timing it NOW, will a Starfleet year last as long as an Earth year? As long as a Vulcan year? A Martian year?

Answer 1

Due to a series of retcons and reversed retcons, I now believe a Starfleet year is roughly 3 Earth years.

I've bolded the important parts below:

Star Trek Guide for TOS

We invented "Stardate" to avoid continually mentioning Star Trek's 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 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.

Star Trek: The Next Generation Writer's/Director's Guide of March 23, 1987

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.

And a note just below it:

Under this system, 1,000 stardate units were equal to approximately one year, since that is the normal timespan between two TV seasons. The value of the century digit nine seasons later was clarified as early as TNG: "Future Imperfect", where the imaginary Jean-Luc Riker asks the computer to display his birthday party of stardate 58416, less than sixteen years in the future according to the episode. The relation to the 24th century could only be symbolic.

Different systems, you say? Not so! One user has done research into how the decimal point really is a fraction of a day. The TOS-era fraction matches up perfectly in TNG 2x11, 2x13, 4x17, 4x18, 5x07, and 6x05 - all various times a fractional stardate has appeared on the screen at the same time as a time of day.

So, to summarize the above:

• Future Imperfect takes place on Stardate 44286, and Jean-Luc Riker shows Will Riker his birthday party on Stardate 58416, less than 16 years into the future. Just over 14000 Stardate unites, to be precise - so 1000 Stardate units is very close to 1 year.
• As noted by the user who looked into times, 1 Stardate unit correlates exactly to 1 day, in both TOS and TNG (and because it does in TNG, DS9 and VOY should as well - they used the same system).
• Finally, TOS 3x24 featured the Stardate 5928.5, and VOY contained 56947.0 - by these, we know the day counter doesn't just hit 365 and reset. One year contains at least 947 days.

There is an additional note on here and Stardates not exactly coinciding with the 1000 = 1 year conversion:

The relation to the 24th century could only be symbolic. The writers of the Star Trek Chronology 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. (TNG: "Data's Day") Stardate 41986.0 was in 2364 according to TNG: "The Neutral Zone", hence the simplified system assumes that stardates 41xxx.x covered the entire year 2364, stardates 42xxx.x the entire year 2365 and so forth.

This can be explained away if a Stardate year isn't exactly 1000 Stardate units, simply very close to it. And it makes sense - one year on Earth is around 365.2425 days. Gene Roddenberry did also state that Stardates do have some natural basis, just like Earth years are based on the sun:

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.

EDIT

Yes, if Jean-Luc Riker was 16 Starfleet years old, that would make him about 48 Earth years old, which is definitely wrong. So, I feel I made a mistake somewhere... Or, Stardates and "years" are just plain inconsistent ;)

Answer 2

The warp drive is an Alcubierre drive, so it does not suffer from the effects of time dilation. It probably means five years as in five earth years. I can't understand the starddate system as it is explained here, there does not seem to be any sort of algorithm that is used, and is explained away as a "complex relationship had been established between stardates and the gregorian calender."

Answer 3

You will never know the full truth about Star Trek years, stardates, and chronology until I write and publish my book on the subject.

My researches show that in the era of TNG it is impossible for there to be a consistent relationship between the number of years alleged to be between two events and the number of stardate units between them.

Either 1) the temporal length of a stardate unit is variable and all time differences are expressed in the same type of years with identical lengths, or else 2) the temporal length of a stardate unit is constant and people use different types of years with different lengths to express time differences between events.

It is my belief that the second possibility is correct and in the era of TNG, DS9, and Voyager stardates have a constant unchanging temporal duration and that people express time differences using years of different length.

It is my belief that the length of a stardate unit was chosen and then people began to talk of 1,000 stardate units as being a "stardate year". Thus seasons in the tNG era are a stardate year long, which is not the year of any planet.

People in the era of TNG tend to express time in either the years of their home planets or the official Federation Year which seems to be much longer than an Earth year if Data used Federation Years in "Where no One has Gone Before". I expect that the ages of Earth Humans are given in Earth years.