[LEAPSECS] Look before you don't leap

[Rob Seaman]

On May 19, 2015, at 10:46 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:

> In message <05E65CAF-D064-4D4E-AA16-195FE7D15A73 at noao.edu>, Rob Seaman writes:
> 
>> On the other hand, the one thing we can be sure about POSIX is
>> that it will ultimately have a finite lifespan.  But a day on Earth
>> (and on Mars and Pluto) will always be a synodic (mean solar) day,
>> whatever decision is made at WRC-15.
> 
> You are wrong in both claims.
> 
> The fundamental problem in POSIX is the value of the integer 'time_t'
> not in how it is represented in human form.  POSIX is therefore
> perfectly capable of handling any calendarial form of time you care
> for, *including* UTC with leap-seconds, (with the footnote that
> a few seconds suffer from an ambiguity of the same kind as the
> "repeat-hour" during DST switchback).

Glad to hear that POSIX handles leap seconds.  What I said, however, was that the POSIX standard was unlikely to prove immortal.  Does anybody think otherwise?

On the other hand the thing that calendars count are mean solar days.  It is precisely the “mean” part that permits calendars to sail unconcerned over daylight saving time adjustments and to ignore the red herring of the equation of time.  Universal Time meant mean solar time before UTC became coordinated.  And mean solar time now and forever will be an expression of the synodic day:

	http://www.cacr.caltech.edu/futureofutc/preprints/files/28_AAS_13-515_Seaman.pdf

If someone thinks otherwise then I suppose she must think a functional calendar could be made out of nothing but 23-hour “spring forward” days?

Rob