Yesterday was a beautiful spring day here in Melbourne, Australia. After a week of heavy rain leading to one of the wettest Septembers on record, the day was glorious. The sun was out, the clouds were white(ish) and there were flowers in every garden.
It’s spring. The weather is getting warmer, the days are getting longer. And it’s light outside when we leave for work. Not yet light when we leave work for home, but that will come. We’ll finally be able to see our garden—which we only see on the weekends in daylight right now. (Thank you, Helen, for making it look so immaculate.)
Like I say, the days are getting longer.
Longer days in summer happen because of the way the Earth tilts toward the sun. The day itself is the time it takes for the Earth to rotate on its axis. A year is the time it takes the Earth to orbit the sun.
Each planet has its own day and year. It may or may not tilt (although tilt is good if you want seasons).
In a spaceship, days, seasons and years are less relevant. When you’re travelling around the galaxy, you don’t care how long the local day or year is. When you move on, the next world will have a different day and year.
So how do you keep time in space?
Human beings have a diurnal rhythm of around twenty-four hours. That’s basically because we are used to Earth’s twenty-four rotation, with its period of light and dark. We tend to wake up in the day, and sleep at night.
In the book we’re currently writing, we use twenty-four hours. It’s an easy time period for readers to imagine. We imagine that ships would have a ‘day’ period of around fourteen hours where the lights were daylight brightness, and a night period of eight hours, where the lights are low.
But is it really a logical period to use?
Years won’t make any sense because each world will have its own year. You’re more likely to have a centralised date, based on multiples of some lesser time periods, and that will be the standard across the whole galaxy.
Think Star Trek star dates.
But what are the lesser multiples that will make up the years?
One thing is likely. Given the human numbering system, it will probably be some variation on a multiple of ten.
Probably the best date system I have ever come across is Vernor Vinge’s seconds, kiloseconds and megaseconds, from his Zones of Thought books. A second is a second. A kilosecond is a thousand seconds. Given there are 3,600 seconds in an hour, this comes out to roughly a quarter of an hour.
Thus a megasecond is 11 days, 13 hours, 46 minutes and 40 seconds, which is roughly of the order of a week. A kilosecond is 16 minutes, 40 seconds, or the length of a short break. A gigasecond 31.7 years, so typical human lifespans are 2 to 3 gigaseconds.