When humans finally manage to colonise another planet, there will be some significant differences between life on that planet and life on Earth.  One of them is the calendar.  Why would the Earth’s calendar be inadequate?

First, the orbital period of the new planet will be different than Earth’s 365.25 days.  Second, the length of the day is going to be different.  Third, with these two basic pieces of information, the year will start at different seasons, and midnight would happen at different times of day.  It would make no sense.

So, what we need to do is create a new calendar and timekeeping system.  I’m going to use my fictional world of Ariadne as an example.  I have yet to figure out the calendar, so I’m doing it on the fly as I write this post.

First of all, we need to determine the distance of the planet from…