In Star Trek Discovery, episode 14, The War Without, The War Within Burnham disturbs Admiral Cornwell at her sleeping quarters, to which Cornwell responds:

I suppose I don't have to tell you it's the middle of the night.

Considering they're aboard a spaceship, how do they determine when is night and day?

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    With the magic of clocks! I even have one on me now!
    – Hans Olo
    Feb 9, 2018 at 16:22
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    @Loki and what time do you set your clock to when you're not near a planet, and are a federation of numerous species and planets all with different day/night cycles?
    – Moogle
    Feb 9, 2018 at 16:25
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    The same way planes keep track of time when they are not in the airport. Also, I guess starships should have atomic clocks (or better), so even with relativistic effects it's easy to keep track of time. Finally, it's known that starfleet has an official time.
    – Hans Olo
    Feb 9, 2018 at 17:18
  • I imagine they have a standard time synced with Earth. Similar to GMT/Zulu time in use today.
    – geewhiz
    Feb 10, 2018 at 0:37

2 Answers 2


Starfleet ships sync their chronometers with nearby starbases on an occasional basis, to keep them in line with the rest of Starfleet. While using stardates to track points in time, most ships used a 24 hour duty cycle based on Earth's time. Within this cycle, the day was broken into thirds (8 hours each), and crewmembers would be assigned different schedules to fill these shifts. You would be on duty for one, another for recreation, and the final one for sleep.

By this logic, we can conclude that Cornwell was either referring to the middle of the 24 hour night, or to the middle of her own sleeping shift.

  • I considered her own sleeping shift, but the way she said it doesn't seem to makes much sense. She could have said "my night" instead of "the night". Also she said "i suppose I don't have to tell you" as if it's completely obvious, but how could Burnham be expected to know every crew member's personal pattern.
    – Moogle
    Feb 9, 2018 at 16:24
  • @Moogle Could have been implied ("I suppose I don't have to tell you it's the middle of the night [for me]"). As far as how to know: there's only three shifts, so the people you see working when you are share your shift, the people you see not working are in recreation, and the people you don't see are sleeping. Also, I think there'd be a particular expectation to know someone's shift before you go knocking, especially if that person is an Admiral.
    – Mwr247
    Feb 9, 2018 at 16:29
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    In TNG, Captain Jellico changes the number of duty shifts on the Enterprise D from 3 to 4 while he's in command of the ship. So, I would hazard a guess that how shifts are organized within a 24 hour "day" depends on whoever is in command.
    – Ellesedil
    Feb 9, 2018 at 17:37
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    @Ellesedil Indeed, "...most ships used a 24 hour duty cycle based on Earth's time" was alluding to that. DS9 also uses a 26 hour, 4 shift schedule.
    – Mwr247
    Feb 9, 2018 at 17:39
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    @Moogle: No one would say "in the middle of my night". "In the middle of the night" is idiomatic. The other isn't. Don't try to reason about how time is kept from the English expression someone chose. Feb 9, 2018 at 23:20

It was established in TNG that there's a day/night cycle used on Starfleet starships (seen in the episode "Data's Day) where the "night shift" is a period of generally lower activity on the ship, staffing is generally reduced, the watch officer is generally someone like the second officer or lower, and even the lights are dimmed.

That being the case, then the ship has to have an onboard day/night cycle.

Now, realistically this is silly; you'd expect a watch system where activity is pretty constant around the clock.

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    "Now, realistically this is silly; you'd expect a watch system where activity is pretty constant around the clock." - Which part? Dimming the lights helps improve everyone's sleep cycles, the senior staff need to sleep some of the time, and following the same routines you did on Earth (or your own home planet) is probably easier for everyone.
    – Kevin
    Feb 9, 2018 at 22:52
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    Dimming the lights in your individual quarters, fine. Dimming the lights on the bridge (as they do) is silly. Feb 9, 2018 at 23:55
  • lighting cycles help sleep cycles. here is a link about some studies showing how sensory input effects sleep cycles. It would be for this reason that starships have a graveyard shift. slumberwise.com/science/could-you-survive-an-endless-night
    – RedOculus
    Feb 10, 2018 at 0:42
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    @RedOculus, yes, but on a spaceship there's no need for everybody to have the same lighting cycle. Everybody on the night shift is worse off as a result. Feb 10, 2018 at 1:05
  • you are saying an inconvenience for a skeleton shift is more important than overall health of the crew. the link I shared shows that people don't know when to sleep without sensory input. furthermore, you have to consider that times of less activity are good for resource management ( a big deal in voyager) and maintenance windows to perform planned downtime work.
    – RedOculus
    Feb 10, 2018 at 17:40

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