Obviously, with no humans living permanently off-planet yet, Earth-style dates and times are the most common system is use, and reasonably so. And it helps that Mars's day is almost the same length as Earth's, so even Martian colonists could use roughly a 24-hour day. (I was always charmed by the idea in the Mars Trilogy of simply stopping the clocks at midnight for a 38-minute "witching hour," a sort of half-hour Mardi Gras every night, which would become a bit of local cultural flavor for people visiting Mars).

But eventually, when substantial numbers of people are living on the Moon and on Mars and on Venus and on ships in between, etc, a 24-hour day and 365-day year will be an increasingly irrelevant timescale. There will probably need to be a "stardate" or some other interplanetary date/time system that is standardized across all planetary bodies, and even later, all solar systems.

A few systems exist today that could work, such as Unix timestamps, but often these measure such small increments (like seconds) that they are better for use by computers than by people. But at some point, a person on Venus will need to say to a person on Titan, "it happened back in February," and I can't imagine that learning the complete calendars of every planetary body will be the most practical option.

Has there been any effort, by NASA or SpaceX or any organization with some kind of practical authority, to establish such a system for tracking long-term times and dates in space? Some interplanetary equivalent of Greenwich Mean Time or Zulu time, for dates as well as hours?

up vote 5 down vote accepted

For the vast billions of people living in a relatively natural environment, our already insanely convoluted time systems in use on Earth are reasonably appropriate.

For the foreseeable future, all our colonists on the moon and Mars will be living indoors almost all the time, in bodies adapted to 24-hour cycles, and for every one of them there will be many more people on Earth working with them -- dozens or hundreds. It makes no sense for them to use any time system other than that of their ground controllers -- either UTC or local time for the mission control site.

Rather than converting between time systems, colonists on other bodies merely need to give up their assumptions that the sun comes up at the same time every day (which it doesn't anyway on Earth, because seasons), that the seasons change the same way every year (which they don't anyway on Earth, because hemispheres), and the like.

If anyone came to me with a suggestion for a new interplanetary time system, I would refer them to this comic.

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    Don't the Earth bound people working with Mars rovers (the current Mars colonists) follow Mars day/night and season schedules? – DJohnM Oct 10 '14 at 18:07
  • Huh. Apparently they do, sort of: en.wikipedia.org/wiki/Timekeeping_on_Mars -- but rather than one new standard, they've created several. I don't see the point, myself. – Russell Borogove Oct 10 '14 at 19:04
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    For Planning or Analysis, no point. But energy and temperature concerns mean Operations take place during Mars daytime for each rover, and not in winter... – DJohnM Oct 10 '14 at 22:00
  • How would a Solar System calendar deal with "time zones" in the shape of light travel time? UTC Earth 6th Oct 2014 relative to time travel time to where Mars is/was then. AFAIK Mars mission teams simply use two separate calendars with a watch on the left arm as well. – LocalFluff Dec 30 '15 at 0:23

In contexts in which there are virtually little relativistic effects, the current standard Coordinated Universal Time (UTC) would apply. As long as communication could be established with Earth, times could certainly be synchronized.

In relativistic contexts, it doesn't make much sense to try to synchronize time. Instead, just give the time in that frame of reference. To someone in another frame of reference, they can compute what the time means to them based on the effects of relativity.

  • "In relativistic contexts, it doesn't make much sense to try to coordinate time." - on the contrary, it makes so much sense that they even decided to call it "coordinate time" :) en.wikipedia.org/wiki/Coordinate_time – pericynthion Oct 7 '14 at 0:09
  • @pericynthion - Read the article you cited carefully. called2voyage is correct. +1. – David Hammen Oct 7 '14 at 18:22
  • @pericynthion Hopefully, replacing the word "coordinate" with "synchronize" will remove confusion for you. – called2voyage Oct 8 '14 at 13:28
  • This is the best answer because the main issue with measuring time during future space travel, i.e. with very high speeds, will be relativity. When speeds are low, UTC can be applied. – Everyday Astronaut Jan 30 at 10:45

Several special-purpose time systems are in use that account for both general and special relativistic effects. These were developed by necessity by the IAU following on from work done by the JPL and other operators of spacecraft in deep space, and astronomers working with planetary orbits to high precisions.

See: Barycentric Coordinate Time, Ephemeris Time, Geocentric Coordinate Time, Barycentric Dynamical Time, Terrestrial Time

There are some briefer definitions and formulae relating the time systems here: http://tycho.usno.navy.mil/systime.html

You need to distinguish between time and calendar. Establishing a universal time is pretty easy, you just need an epoch and count intervals from there. Establishing a universal calendar on the other hand is pretty unlikely and is quite likely to be unnecessary.

Converting between time scales is fairly easy, just change the interval scale and the epoch (the formula is the same as the one you use for converting from Fahrenheit to Celsius just with different constants) then adjust for relativistic effect.

Converting between calendars, on the other hand, requires extensive knowledge of local historical politics. It is highly unlikely that the politics of earth would be of interest to a civilisation of regular space dwellers.

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