Astrotropes: Universal Time

Think of the biggest oversight you can in all of sci fi. One thing so fundamental to our daily lives that the idea doesn’t even register that it should be questioned. Unfortunately, it’s also the one thing which should literally always be questioned. This post? It’s about time. No no, literally, it’s about time.

Anyone who’s ever been on a long haul flight will know all too well how it feels to suddenly find yourself on a different time schedule. For instance, when your brain thinks it’s 2 am and you really need to get some sleep, but all around around you it’s 9 am locally and people are starting work. We’ve evolved to have a sleep pattern based around a cycle of day and night and even moving around our own planet can be enough to throw us out of sorts for a few days. But what even is a day, exactly?

Consider factoring in an added complication – suppose the place you’re going to has a different length of day! We all know that a day on Earth lasts 24 hours, but this is only true on Earth. And even here, a true day is technically 23.94 hours. Neighbouring Mars has a day of 24.6 hours, but Venus has a day which lasts 5832 hours (or 243 Earth days)! Meanwhile, a Jupiter day lasts 9.9 hours, a Neptune day is 16.1 hours, a Pluto day is 153.2 hours, and a Titan day is synchronised with its orbit of Saturn and so lasts 382.6 hours. As may be fairly obvious by now, there’s a lot of variation. Obviously, trying to stay awake for 382.6 hours at a time would be ridiculous but all the same, planets with days which are perfect multiples of 24 are really not likely!

Then, let’s bear in mind that a solar day (the length of time between two sunrises) is not necessarily the same as a sidereal day (the length of time taken for a planet to rotate once). No, not even here on Earth, which is why some astronomers may frequently refer to times in Local Sidereal Time. The day lengths I mentioned in the paragraphs above are sidereal days. A planet like Venus, for instance, with a combination of a really slow rotational velocity and a relatively fast orbital period will have a significantly shorter solar day that its sidereal day.

Are you confused yet? The TV Tropes article on this also includes this amusing little snippet of text concerning Mercury:

“It gets weirder – one Mercurian day is about 176 Earth days, or precisely two Mercurian years. (The precise 1:2 ratio is due to a 3:2 spin-orbit resonance.) Yes, that’s right – on Mercury, a day is two years. (Feel free to speculate about whether dates like April p.m. have any meaning.)”

At its heart, the trope here is that the issue of time is almost always ignored in sci fi. Instead, the entire universe works by some kind of magical universal time whereby it’s always the same time wherever you are. Which is odd, because this isn’t even the case here on Earth. The only time I recall time being mentioned in sci fi was an episode of Firefly, where one character greeted another with “good afternoon” before being told that it was still the morning where they were about to land.

Star Trek, however, is one of the main offenders, not only allowing instantaneous communication across hundreds of light years, but also making it virtually always daytime when they call someone light years away. And making it always daytime as soon as they arrive at whatever planet they’re travelling to.

A little more reality here would be great in sci fi. It doesn’t even need to impact the plot greatly. To have a character simply mention when arriving at a new planet that they should wait 7 hours before going to the surface so that they can meet people during the day, for instance. Or for two characters to have a fleeting conversation about how the 53 hour day on this world takes some getting used to. Even simply giving a character interplanetary jet lag. Anything other than arriving at a planet and finding that it’s conveniently the middle of the day irrespective of what part of that planet they’re going to.

Major plot points could even be woven around things like this. A character who has to frequently adjust their body clock in this way may develop a nasty addiction to stimulants or other drugs in their attempts to cope. They may find themselves with insomnia after leaving a planet with a long day. The Warhammer 40000 universe even sees humans with modified bodies so that they can rest half their brain at a time the way dolphins do.

Please, sci fi writers, pay even passing attention to the concept of local time? It wouldn’t take much, but it would add a huge amount more realism to your stories. Ignoring time is almost as bad as never bothering to give your planets any weather.

It is, however, noteworthy that by remarkable coincidence, one Mars day is only slightly longer than one Earth day, and one Titan day is very close to being 16 Earth days.


Image credits:
Banner – NASA
Upper – Harvard Smithsonian CfA
Middle – NASA
Lower – sanmonku @ deviantART


About Invader Xan

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One Response to Astrotropes: Universal Time

  1. Ash says:

    Interesting post, especially the bit about weird day lengths messing people up.

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