In Voyager, Season 1, Episode 6 (Eye of the Needle), Captain Janeway communicates with a Romulan vessel in the Alpha quadrant via a probe relay in a wormhole.

At the end of the conversation they have while she's in her quarters, the Romulan says "good night".

How did the Romulan know that it was night time on Voyager? (I know the answer now... but my more general question still stands.)

Do the Romulans follow the same day/night cycle as Starfleet? Do any of the humanoid species in Star Trek follow a different day/night cycle?

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    Was it actually "night" on the ship? (Given the nature of that particular wormhole, it's not really necessary that anything was synced up anyway) – Izkata Jan 15 '14 at 5:04
  • @Izkata I don't know. If I've made an incorrect assumption, please correct me. That would be part of a good answer. – user21032 Jan 15 '14 at 5:09
  • Oh damn... I just finished watching the episode! It was a special wormhole, making the time sync just coincidental. I guess Kim may have just told the Romulan that Janeway was asleep. – user21032 Jan 15 '14 at 5:14
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    Watched that episode yesterday. :) I've asked myself the same question, then I remembered, that she said something that preparations will be made in a few hours - maybe they just knew that this means a little time for resting. – Trollwut Jan 15 '14 at 7:30
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    Regardless of when it is night or day (since it is not "night" or "day" at the same time across a single planet, or even large countries, I imagine a shift-based system is used so the ship is always manned...) it's interesting to know if different humanoid species observe a different length of day. For example, instead of 24 hours a 34 hour clock. Or perhaps a species requiring less sleep may not observe the concept of "night" after progressing to life away from a star. Which are you questioning? – Gorchestopher H Jan 15 '14 at 13:10

The whole concept of day/night has to be basically rewriten on a starship. Day/night is after all a product of sunrise/sunset and when in orbit, the sun may rise and set 2-3 times an hour.

I suspect that there's a universal star fleet time that is used in communication, probably based on star fleet headquarters on Earth (where there is a defined day/night).

With regards to the fact that the voyager crew and aliens they encounter all seem to be on the same time scale, I suggest that this is simply a plot device to expediate the story. Personally I'd love a star fleet captain to hail a war bird and see the klingon captain turn up in pastel coloured pjamas !

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    +1 for "plot device". I always wondered how the action always seems to happen during the day watch, when all the main officers are on duty. – Daniel Roseman Jan 15 '14 at 9:53
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    There are some episodes of voyager and enterprise (e.g. a night in sick bay) that take place during the night. In these episodes the lighting in the corridors is noticably reduced, inferring that they do have night & day. – Pat Dobson Jan 15 '14 at 10:09
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    And nothing ever happens at night. See Data's Day – Mr Lister Jan 15 '14 at 10:10
  • @Mr Lister - But then, Data is a special case as he doesn't require sleep (although he might 'simulate' it in his quest to become more human) – Pat Dobson Jan 15 '14 at 10:44
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    There are also several occasions in Voyager particularly where Janeway or other main characters are in bed and woken by a hail from the bridge. Other times they're off duty eating what appears to be an evening meal or are at breakfast, or in the holodeck etc... so it's not like we NEVER see events where time isn't synced. – Jon Story Nov 24 '14 at 14:07

Day/night cycles are not always aligned.

This a minor plot point in the Enterprise episode "A Night in Sickbay". The Enterprise is in orbit around the planet Kreetassa. The Kreetassans are in the habit of getting offended over things that Enterprise crew thinks are tiny. When it is nighttime onboard the Enterprise, a Kreetassan calls the ship, and is offended over something that Hoshi thinks is tiny.

KREETASSAN [on viewscreen]: Why haven't you adjusted your time to our capital city?

HOSHI: I apologise. We weren't aware that it was required.

KREETASSAN [on viewscreen]: It isn't a requirement. It is simply a courtesy. Something your species doesn't seem to understand.

I'll also add that Deep Space Nine keeps a 26 hour day. I don't know if there's proof, but I've read people say that that is because Bajor has a longer rotation period than Earth does. If that's true, then Deep Space Nine is out of sync with other Federation vessels.


Communication was not visual never the less, a captain is usually on the bridge unless off duty; and presumably out of courtesy, wished her a good evening. It's highly unlikely all habited worlds share the same time day/night standard. Bajor for example has 26 hours per day. That's why Starfleet uses Stardates as opposed to clocked time for mission logs. However personnel use "Military time" in presumably 24 hour intervals. However Starfleet maintains Federation time beacons which implies the fleet regardless of where it is in the galaxy, operates by the set time regardless of differential, in a DS9 episode, Sisko mentions "Station time" meaning they have their own chronometers kept in correspondence with communication with Bajor.

In real life, astronauts aboard the International Space station maintains it's clocks in Coordinated Universal Time or as we call it Greenwich Mean Time.

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