So I want to write a Sci-Fi where humans have spread across the solar system and into the galaxy. There are multiple stories going across at several different times. E.g.:

  1. Aliens attack Pluto
  2. 3 weeks later, aliens arrive at Mars
  3. Flashback scene to a few years ago, when Earthlings missed sign of invasion, leading to destruction of Earth.

Currently, I'm using Earth dates, something like: July 28 (Earth date), aliens attack Pluto, August 20 move to Mars etc. But people on Pluto wouldn't use the Earth calendar; they would use their own system. When those people talk about dates, what should they say? How can I convey to my readers the dates of these various events (and the relationships among them) when the calendar systems used by the characters would be different?

PS: I don't want something confusing like the Stardate system. I don't want to be explaining to my reader how my calendar works.

  • Currently discussing this in chat. Mar 3, 2013 at 17:34
  • Shantnu, I've made some edits to your question to try to bring out the underlying writer's struggle more clearly, specifically the difference between what your readers know and what your characters know. If this took it away from what you meant to ask, please let me know (and of course feel free to edit further or roll back). Thanks. Mar 3, 2013 at 19:54
  • 2
    @MonicaCellio , your edits are perfect. I typed the post before lunch, so my thoughts may have been less than coherent :) Mar 3, 2013 at 21:20
  • PS Your title says that events are spread over the galaxy, but the text indicates that they are simply spread over the solar system.
    – Jay
    Mar 5, 2013 at 17:24
  • @Jay, that was an example. Mar 6, 2013 at 13:23

6 Answers 6


I can think of a few ways:

1) Cheat. This was how Tolkien did it, so you'd be in good company. He just listed somewhere in the appendices that "Year 5798 by Gondor's calendar = 144 Shire Reckoning" and let the readers do the math.

2) Make the characters work out a solution. If you have characters on Terra and characters on Pluto who meet, they're going to have to work out some way of syncing their calendars.

3) Meta. At the beginning of a chapter, just announce as part of the header what the date is:

July 20, 2056 Terran Time
12 Fizzbinth of Shar, Plutonian Time

If you equate them at the beginning of the chapter, it will be clear that the two dates are the same, and then you can advance them separately (or together) as needed.

4) Reset the calendars. Call it 1 A.I., Year one after invasion.

At some point, unless all your characters are using a calendar which your reader understands, you are going to have to do some amount of explaining.

  • 2
    I like #3 the best
    – CQM
    Mar 5, 2013 at 4:05

If you are just using dates in narration, as opposed to in dialog, you could just use Gregorian dates. When an American or European writes a history book today, they routinely use the Gregorian calendar even if that's not the calendar used by the people they're talking about. This only matters if the date itself is significant to the subjects.

If the people on the other planets are colonists from Earth and not aliens native to that planet, it's quite possible that they WOULD use an Earth-based calendar. Especially if they're in regular contact with Earth people. Sure, the Gregorian calendar does not match the orbital period of Mars or Pluto, but the convenience of using the same calendar on all the planets in the solar system would likely outweigh any advantage of having the calendar match the orbital period. I think this is what most science fiction stories do: They just have the characters express time in "standard Earth years" and leave it at that. It's not implausible, because the same reasons that make it simpler for the reader would make it simpler for the people involved.

Of course if you're talking about aliens, I wouldn't expect aliens to use the Gregorian calendar. That would be a rather jarring disconnect.

So failing that, if for one reason or another you must have these people have their own calendar, I don't see how there is any way out of explaining it, at least to some extent. You can't just say that one event took place on the Third of Foo and another took place on the Lesser Mordac of Hegenev and expect the reader to somehow know which came first and how far apart they are.

Unless you want the workings of the calendar to be a major element of the story, even a simple calendar would be a pain to the reader. Like if you say that the Martian calendar has 20 months and here are their names, and the months are 33 days each except for the 2nd, 4th, 7th, 9th, 11th, 13th, 16th, and 17th, and the 19th on leap years, and leap occur two out of every five years, etc. (I believe that adds up to the right number of days, if I made a mistake, not really the point), that's about as simple as you're going to get, and it's an awful lot for a reader to understand and remember just so he can grasp when things are happening.

I think the easiest way out is just to translate the dates. As I said, if it's in narration, you can simply say, "this happened on August 3". What the date is on somebody else's calendar doesn't matter. If it's necessary for a character to say the date, you could translate. Like:

"We must do this by the High Mordac of Hegenev," Franslac said.

George did a quick translation in his head: That would be August 3.

Of course if you're doing this all the time, that could get tedious for the reader. That's why, I think, most writers avoid the problem.

Addendum 3 years later

When we give alien dialog in a book, we routinely give it in English, even though it would seem somewhat unlikely that aliens from another star system would speak English. We have the aliens give distances in light-years, even though they would surely not use this particular unit. Etc. The reader understands that you are translating. So translating dates also would not be implausible.

Where it WOULD get implausible is:

(a) Anything that assumes that dates "line up". Like, if a crucial plot point hinges on an event happening at the stroke of midnight on July 8, I wouldn't expect that to be the same time at Star Fleet Headquarters on Earth as it is on the capital of the alien planet. That doesn't work with time zones here on Earth. Similarly, we wouldn't expect the length of a day or a year to be the same.

(b) I wouldn't expect aliens to attach cultural significance to the same days we do. If in a book an alien says, "The invasion will begin on November 12", I'd accept that as a translation. But if an alien says, "We're delaying the invasion until after the new year", that seems to say that they start their year on January 1 like we do. "The invasion will begin the day after Christmas" -- unless you've given some reason why the aliens celebrate Christmas or at least are aware of it, this would be very jarring.


From the point of view of practicality it's pretty hard for human beings from earth to adjust to other solar cycles etc. We're not built to operate in days much outside of our current 24 hour clock. People working in locations where the days are unusually long or short (or practically non-existent e.g. the South Pole) experience bizarre physiological and psychological effects.

For this reason most SF writers fudge the issue by referring to "Standard Cycles" or "Solar Days" or "Median Orbits". The nomenclature is alien enough to be exotic whilst clear enough to imply that time passes at the same rate. Star Trek is the exception not the rule. I think the "Stardate" thing was just a device to make the voyage of the USS Enterprise appear to be timeless and epic.


Is there one POV character or multiple?

I would always aim to put the calendar according to the POV character. If it's just one character, it's pretty easy. Post through their perspective only. They can always make a comment when talking to other alien characters. "It happened in 3987. Oh, I guess that'd be #$nei9 according to your calendar."

If you switch between multiple POV characters, you can try a few things.

  1. Keep the calendar aligned with the POV. This may mean characters explaining things to each other a bit.
  2. Create a galaxy standard. You could create an accepted standard year that pretty much every planet knows. Even if they prefer to keep their own calendar, they would reference it off of the galaxy one.
  3. Create a diagram / reference guide for appendix. Display all relevant calendars beside each other so you can see where events line up on each. Readers can look up most of the dates in there.

How important are the years?

Perhaps characters could just work off of major events. Is it important for you to be specific in terms of how many years have passed between events? If there aren't too many events, I think you could avoid it altogether. If there are quite a few, I could see needing a calendar / dates.


Dates and times are internationally standardized in ISO 8601. The ISO 8601 dates use the Gregorian calendar and 24-hour time, i.e. “March 15, 2015 at 23:11:01."

Your readers will potentially include the entire population of Earth, and as such, ISO 8601 dates are appropriate. People who use some other kind of date system in their region will know how to convert back and forth from ISO 8601.

In the future, people on Pluto may use ISO 8601 or they may use some kind of Pluto time, but in that case they will also know how to convert back and forth from ISO 8601.

Of course, in the future, ISO 8601 may be updated in some way, and you may want to tackle that creatively. But in that case, your readers may not know what you are talking about. In theory, English may not exist in the future you are creating, or may be very different (it’s not that long ago that English and German were the same language) so if you are writing in English, you might also want to just write dates and times in ISO 8601.

Generally speaking, writers and editors and publishers should follow ISO standards these days because your audience is potentially anyone, anywhere in the world, and exchanging data internationally is why these ISO standards exist. Again, your readers will either already follow the ISO standard, or they will know how to convert the ISO standard to their regional standard.

Just Google “ISO 8601” for more information.


Focus on your storytelling and how you structure your narrative. This will bring clarity to the timeline more than the syntax of the calendar you end up choosing. Recall your favorite science fiction authors - the vivid world they created and character arcs were probably primarily what drew you in, more than the delight of the alien language or non-earthly systems presented.

Storytelling and structure are your "cake". The solar-system terminology you ultimately settle on will be the "icing" on that cake.

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