On Fri, Mar 09, 2018 at 08:03:33PM -0500, Jeff Zeitlin wrote:
> Noted, although 'discussion' of fiat calendars would only amount to a
> couple of sentences, perhaps at most a short paragraph.

A calendar used beyond the surface of a single planet is nearly always
going to be a fiat calendar everywhere but at most one place.  Whole
books could be written on the variations and cultural ramifications of
adapting a "foreign" calendar to local conditions.  With enough
engineering, perhaps local conditions coudl be adapted to match the
calendar.

There are also other species to consider: most Earth animals display
marked diurnal variations in their functioning, and have limited
ability to adapt to other periods.  Many also display strong
species-wide annual variations, although there is little evidence of
this in humans.

It seems likely that species with strong biological cycles on various
timescales will maintain some sort of separate calendar featuring
those, regardless of whether some other calendar is "official".

For example, it seems to me quite likely that any human culture will
maintain some timekeeping measurement approximating an Earth "day",
with a length around 24-26 hours, even if immersed in a culture with
other calendrical standards.

> That's not really a calendar, so much as an extended clock/timer - you
> don't say "My birthday is every 31.5 megaseconds at kilosecond 36."

I've seen it used for calendrical purposes in some fiction, though it
strains my disbelief in the sense that 100 ks is just enough longer
than a biological "day" to be implausible as a calendrical unit.

If such a timekeeping system has been in use for a long time and
"birthdays" are celebrated, they're not likely to be at odd multiples
like that.  They would much more likely be at numbers like 100 Ms, and
possibly be a bigger deal than those celebrated only every 31 Ms.

> Even H.Beam Piper's use of hours instead of seconds in _Four Day
> Planet_ was really clock/timer rather than calendar.

I've read a book that did have a spacefaring culture using regular
power-of-ten units for the calendar, but can't recall the book's name.
The base unit was "chron", a bit more than a minute.  It didn't match
any particular planet of course, but then any other system would fail
to match all but one planet anyway.  I vaguely recall that the planets
encountered during the story were rather primitive (TL6- in Traveller
terms), and at least one had a "barbaric" calendar of their own.

- Tim