I understand how the stardate system works in Star Trek and it doesn't really lend itself to casual conversation ("see you on star date 41645", as opposed to "see you on Monday") or recurring events such as birthdays ("My birthday is on 4X645" rather than "My birthday is on July the 5th"). How do they manage this in-universe?

In fact, do they even use relative terms such as "tomorrow" or "yesterday" ("Yesterday's Enterprise" of course, but that's out-of-universe). I can't remember any examples.

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    It's a minor plot point that they refer to the future in number of days in Wrath of Khan (e.g., the repairs will take three days). Which isn't quite the same thing as saying tomorrow, but is pretty similar.
    – Nolimon
    Commented Mar 4, 2020 at 14:14
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    Wait. Dividing time into units of 12... then units of What???? 28-31 depending? What the actual F???? Then 24 then 60 then 60 but sometimes 59? What is this? Harry Potter??? Commented Mar 4, 2020 at 22:57
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    "Captain's Journal. Stardate April 13th point two."
    – Schwern
    Commented Mar 4, 2020 at 23:26
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    Khan Noonien Singh sure had a real bad case of the Mondays. Commented Mar 5, 2020 at 1:07
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    The funny thing is that relativity makes any interstellar time system meaningless.
    – Spencer
    Commented Mar 6, 2020 at 17:18

3 Answers 3


Yes, they use days of the week as well as months.

It's a running gag in Star Trek: Generations that the necessary equipment will be installed on Tuesday.

HARRIMAN: We don't have a tractor beam.
KIRK: You left Spacedock without a tractor beam?
HARRIMAN: It won't be installed until Tuesday. ...Ensign Sulu, try generating a subspace field around the ships. That might break them free.
CHEKOV: How big is your medical staff?
HARRIMAN: The medical staff ...doesn't arrive 'til Tuesday.
CHEKOV: (mutters in Russian) (to journalists) You and you and you. You've just become nurses. Let's go.
KIRK: Load torpedo bays, prepare to fire on my command.
DEMORA: Captain, ...we don't have any torpedoes.
KIRK: Don't tell me. ...Tuesday.

(Star Trek: Generations, Transcript here)

I briefly looked through other transcripts as well, and I am pretty confident that they are using the days of the week the same as we do. For example, this is from DS9: Crossfire:

KIRA: What is it?
ODO: I don't quite know how to say this, but I've given it a lot of thought, and er...
KIRA: Go on. Just say it.
ODO: I'm afraid I won't be able to make our Tuesday morning meetings anymore.

We can also frequently see them using months, for example, in DS9's "Whispers":

O'BRIEN: I mean, the way they were acting, they might've been trying to pull off one of those surprise parties that I can't stand, only my birthday's not until September, and believe me, as it turned out, I had nothing else to celebrate.
BASHIR: Ah, there he is now. I've been waiting for you, Chief.

There are also numerous other cases where they refer to days of the week or months.

They also use relative terms, for example in TNG's "Qpid": It starts out with:

Captain's log, stardate 44741.9. We have arrived at Tagus Three where the Enterprise is to serve for host of the Federation Archaeology Council's annual symposium. I look forward to giving tomorrow's keynote address with great anticipation.

Or here, in DS9's "Sanctuary":

KIRA: You wanted to see me, Commander?
SISKO: Actually, what I'd like to see is next month's duty roster.
KIRA: You'll have it on your desk first thing in the morning.
SISKO: That's what you said yesterday.
KIRA: I know, but I just spent the whole day yesterday...
SISKO: Talking to Minister Ro.

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    Voy: Year of Hell - HAKOTAY: Happy birthday. JANEWAY: Happy what? CHAKOTAY: Today is May twentieth. JANEWAY: Is it? I thought we were still in April. Guess I've lost track of the time.
    – Valorum
    Commented Mar 4, 2020 at 14:39
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    This answer only confirms the existence of Tuesday. =P
    – Harabeck
    Commented Mar 4, 2020 at 14:39
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    VOY: Tuvix - TUVIX: If memory serves me, Wednesday is the day that Neelix always cooked Trellan crepes. Your favourite meal?
    – Valorum
    Commented Mar 4, 2020 at 14:41
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    VOY: Someone to Watch Over Me - DOCTOR: Mister Neelix is hosting a reception for the Kadi ambassador on Thursday night. Not only will Seven arrive with a date, she will have him eating out of the palm of her hand.
    – Valorum
    Commented Mar 4, 2020 at 14:42
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    There's other examples. The premiere of Star Trek: Discovery gave the stardate and the Julian calendar date, later they mention the Battle of the Binary Stars was six months prior, talk about how many years have passed since so and so happened, and so on. Commented Mar 4, 2020 at 18:01

Worf's son Alexander born on the 43rd day of Maktag, Stardate 43205 (2366) TNG episode: "New Ground")

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    I gave you an upvote for the lateral thinking. I didn’t specifically ask about human/Earth days of the week after all.
    – Darren
    Commented Mar 5, 2020 at 7:43
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    It would be great if you gave some more input on when this was mentioned on-screen :)
    – Philipp
    Commented Mar 6, 2020 at 9:14

In the UFP and other known space travelling societies the old time systems of home planets and colony planets are still used. Earth people still use various Earth calendars with years, months, weeks and days to keep the date, and Earth people still use time keeping units like seconds, minutes, and hours.

So people who live on a colony planet or space station or moon base equivalent would use both the local time and date keeping methods to keep track of changes in local temperature and light, etc., and also the date and time keeping system of the home planet of their species to keep track of their ages and celebrate religious or secular holidays, etc., etc.

And no doubt they have simple computer clocks in their various gadgets to keep track of the time and date in both systems for whenever they need to know it.

And when people from various different species get together there are several different sets of date and time keeping systems involved. But converting between such systems should be no problem for the computerized time keeping systems they would have available.

And apparently stardates are used as an interspecies date keeping and time keeping method. Presumably people convert their units into stardates to communicate with aliens and when they are told stardates translate them into their units.

Memory Alpha says:

Stardate systems were used in certain cultures as early as the 2150s, when the United Earth government worked with Gregorian calendar dates. In 2154, Degra, a Xindi-Primate, sent a coded message to Enterprise NX-01 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. (ENT: "Damage")

The script for "Damage" says:

T'POL: I discovered a set of coordinates embedded in the document.

ARCHER: It's not a star system.

T'POL: There was another embedded number. A stardate, three days from now.

ARCHER: How far away are the coordinates?

T'POL: Four light years. We'll need at least warp three to make it in time. It's unlikely that Degra will wait beyond three days.

Since stardates are not used by Earth people in other Enterprise episodes, the stardate mentioned in this episode should be in a system used by various space traveling species in interspecies communication. This stardate system should have been around for years, decades, or centuries before the first episode of Enterprise, and might have been created by various non human societies before humans ever had warp drive.

If that stardate system was created by non humans with no input from humans, stardates would not be based on Earth time units. And if that stardate system was the system that came to be used by Starfleet in the era of TOS and the era of TNG, people who suppose that stardates are based on Earth time units would be wrong.

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    Note that they still talk about distances in "old" time units: light years. And which planet does the federation use as reference for that year? Commented Mar 5, 2020 at 10:53
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    T'Pol knew that it was three days in the future, indicating that Vulcans also had an understanding of stardates at that time. (ENT: "Damage") - or that the universal translator can figure it out.
    – Rob Grant
    Commented Mar 5, 2020 at 11:38

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