I enjoy fielding questions on Catholic Answers Live about humanity’s forays into outer space, such as this one: “How would the Church adapt its liturgical calendar if we colonized another planet or the moon?”
Well, it’s going to depend on where the planet or moon is and how fast it rotates. Humans are biologically designed to have a wake-sleep cycle that is synced with the day-night cycle on earth. If we’re in an environment where the day-night cycle is radically different from what we’re programmed to work with, we just ignore it.
For instance, the International Space Station goes around the earth in about forty-five minutes, meaning the astronauts on board get twenty-two minutes of light and twenty-two minutes of dark. There’s no way they want to fall asleep every twenty-two minutes and then wake up twenty-two minutes later for the duration of their mission.
Thus, astronauts on space stations ignore their environment’s peculiar day-night cycle. Instead, they keep a regular Earth-based day-night cycle for their sleeping and waking periods.
The same would be true of any other planet or moon that has a radically different rotation rate. And if humans are keeping a normal terrestrial day-night cycle and ignoring the rotation of the object they’re on, then they would likely keep a terrestrial calendar. They wouldn’t modify the calendar because they’re keeping the same day-night cycle.
Now, what about other planets like Mars, which has a rotational period close to that of earth? Its day is almost the same length as earth’s. It’s a little bit different, but humans there would probably adapt to a Martian day-night cycle, and that means their days and nights would get out of sync with the days and nights on earth.
However, I don’t think that on Mars there would be a need to change the liturgical calendar, because Mars is very close to earth. It’s only a few light-minutes away, and as a result it would be very easy to stay in contact with earth and continue to use the terrestrial liturgical calendar. Even if their Sunday slides a few hours from Sunday on earth (because of the difference in the day lengths), you can still approximate that. So, they would still have the same kind of Sunday cycle, they could still celebrate Christmas and Easter at the same times, and so on.
But what if you go further afield—like out of our solar system? In that case, there’s no easy way to communicate with earth because of the light-speed limit. If you were on a planet with a similar rotation period to earth, I could see the local church in this other solar system developing its own liturgical calendar based on the local planetary rotation period.
However, I suspect that even then—even if they came up with new holidays and new liturgical seasons—they would still keep Christmas and Easter at the same time that they’re being celebrated back on earth, because that’s something you could always calculate.
So, I think that there could, in another solar system, be a different liturgical calendar with some similarities to ours; but here in our solar system, we’re so close that I don’t think we would practically develop different liturgical calendars for other planets—at least not any time in the foreseeable future.