So, say I'm writing this story that takes place on a giant starship travelling from galaxy to galaxy (delivering goods or something like that). This ship was created and inhabited by one race initially, but through exploration and confrontation, it is now a permanent home to multiple races (at least 3). Most who inhabit this ship are descended from multiple generations of people who have lived on it their entire life.

My question is, with the lights and power to the ship generally being on all of the time, how will this ship measure the passage of time? It doesn't make much sense to me for them to measure time the same way the original race did, because in a ship constantly travelling, measurement based on one celestial body's movement doesn't seem very logical. Plus the whole multiple races thing. I'm also aware they could measure it by how long ago it took off or something, but I'm looking for a more efficient minutes-hours-days kind of measurement.

Bonus question: To add to this, what would their sleeping schedules look like, considering most have gone their entire lives without orbiting a star or anything else? In fact, I'm planning on adding untamed animals to this ship, so would would their sleeping schedules look like?

  • 3
    $\begingroup$ “measurement based on one celestial body's movement doesn't seem very logical.” Tradition is one heck of a drug. $\endgroup$
    – Topcode
    Commented May 6, 2022 at 15:12
  • 1
    $\begingroup$ You have a common unit of time. You have multiples and submultiples of that unit. You have shifts consisting of some number of units of time. You have days consisting of three or four shifts. Like we do for example on nuclear submarines, which can go months without ever seeing the sun. $\endgroup$
    – AlexP
    Commented May 6, 2022 at 15:18
  • $\begingroup$ Related and of interest: Time standardisation in an FTL universe, Universe-wide time-keeping. and how-would-you-make-a-universal-measurement-of-time. $\endgroup$ Commented May 6, 2022 at 16:09
  • 1
    $\begingroup$ Shipboard time is a thing. Ocean going ships often track time independent of origin or destination. $\endgroup$ Commented May 6, 2022 at 18:27

5 Answers 5


I assume all of these species(!) evolved on a planet. Their biology will be atuned to their planets' day-night cycles, so it will still make sense to have artificial cycles on the ship. (see Circadian Rhythms)

Having the lights on unchangingly all the time is a really bad idea, in fact this is considered torture in prisons.

In fact, it will most likely be necessary, or at least comfortable, to have different sections with different cycles for each species, unless they are close enough.

For timekeeping, they will have to agree on a standard day, just like any multi planetary civilization will have to.

How they create longer cycles, like weeks, months, and years, is rather arbitrary, and will probably be determined by tradition.

  • 1
    $\begingroup$ This is a good answer. It wasn't the answer I was looking for, but it made me realize that what I said in the post is not quite what I was actually going for, and I'm probably gonna change the setting quite a bit. So I guess this question is redundant now, but thanks for the response, very informative! $\endgroup$ Commented May 6, 2022 at 17:02
  • $\begingroup$ This is more or less the answer that I was going to give. IF the starship doesn't need to keep time with a particular planet then this makes the most logical sense. Tune the clock to the body clock of the passengers or crew. Controversially, humans circadian rhythm is actually closer to the Martian cycle than the one on Earth. Nobody knows why. $\endgroup$ Commented May 8, 2022 at 18:21
  • $\begingroup$ I wanted to give the same answer except for the days. It would be annoying to be a species where your day/night cycle is for example 0.79 the length of the calendar "day" as there is no easy way to know what day you are in. Maybe you should have universal seconds, minutes and hours but days are different for each species and expressed by a %. Say "we'll meet at the 33rd Aday 40%", indicating the species with a letter, the day of the week/month/year you want to meet and the % of the day compared to that species day cycle. $\endgroup$
    – Demigan
    Commented Aug 30, 2022 at 11:03

Atomic clock?


An atomic clock is a clock that measures time by monitoring the frequency of radiation of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific frequency of electromagnetic radiation. This phenomenon serves as the basis for the International System of Units' definition of a second.

Your ship has a clock on board. It tracks time by watching cesium atoms. This is how existing atomic clocks work. They are super accurate.

Watching pulsars

Pulsars pulse at fixed rates. Your ship observes one or more of these and calculates the passage of time by counting pulses.

Big windup clock.

There is a big windup clock that shows the time, day, month and year. It is not original to the ship but was brought on board by one of the arriving peoples. Their descendants keep it wound up and cared for. They don't let other people touch it because they might break it, but other people can look at it and everyone does. The keepers of the clock say that it is from their home planet but no-one knows for sure. Some of the other people say among themselves that the ancestors of the clock keeper people stole it.

The ship had a built in time system which may or may not still be working. People like the big windup clock now because it is pretty and cool and makes good noises.

  • 2
    $\begingroup$ +1 for an intergalactic ship using a wind up clock. They could even build anew religion around it. $\endgroup$ Commented May 7, 2022 at 5:16

Day zone and night zone

Have the ship split into two parts; a night zone and a day zone. The day zone is brightly lit, while the night zone is only very dimply lit. You can travel between the zones via designated corridors or via your own quarters. Each quarters has one door for the night zone and one door for the day zone. Maybe some establishments like for example a mess hall (or restaurant) may be split in two, with a shared kitchen serving booth sides. This way each species can follow their own day night cycle.


They will follow the same standards for more granular time(minutes days weeks seconds etc) that they had before they took off, the same way as has happened throughout history, while the time will likely be dated from launch, that is the years since the launch.

The reason their standards of time wouldn't change should be pretty obvious--you need technical capability aboard a ship, with a lot of components, work, etc,being time sensitive. It makes very little sense to try and change the time metric when it would certainly be detrimental.

Also, when the French were creating the modern metric system, they a.so attempted to change the metric of time to a decimal-based scale, but that did not take. Our time metric comes from a variety of places, and it very rarely changes. The setup of the week, for instance, hails back to the roman empire, and particularly the Jews, who had there Sabbath every seven days. An entire people refusing to move or work every seven days cemented the week system we have now, and it hasn't changed much since.

Of course, besides the way of dividing up the day into various fractional parts, their is the basic cycle itself, which would be built into the organism's biology, and thus much harder to change then arbitrary numbers, and its unlikely for that to happen given how hard it is for the numbers to change.

Once again, because of the aggressive timekeeping measures of any technical enterprise(think financial groups, etc) that will be aboard your ship, as well as any time-sensitive action(keeping constant acceleration for example) will mean that times will remain very constant, and while sleeping schedules may change(in fact they may need to, because of various actions that may need to be taken by members of the crew), the actual time that a "day" lasts won't, unless some form of irrational totalitarian is in charge, in which case said person may mandate a change, and than, for the same reasons that time couldn't change previously, that change would stick.

  • 1
    $\begingroup$ The seven day week long predates Judaism. it originates, based on the known evidence, in Sumeria. $\endgroup$ Commented May 10, 2022 at 19:22

The spin of the ship

The ship is an enormous Cylindrical craft (Rama, O'Neill Cylinders, Suchlike) and spins for gravity.

The passengers don't necessarily notice the spin, their world simply curves on itself, but if you can see out, you can watch the stars whirl around and around at a steady pace.
You could set your watch to it.

A mile-across spinning cylinder would need to turn once per minute, so there's your basic unit of time.
The rest is simply keeping track of the number of times the ship has spun.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .