Re: [LEAPSECS] Leap-seconds, the epsilon perspective

From: Ken Pizzini <ken_at_HALCYON.COM>
Date: Wed, 29 Jan 2003 01:16:06 -0800

On Wed, Jan 29, 2003 at 12:33:48AM -0800, Steve Allen wrote:
> > What for? Why should we (the people of the Earth) care about mean
> > solar days? For some purposes, apparent solar time is important, but
> > most of the time it's civil time that counts. Why should that be tied
> > to mean solar days?
>
> Partly because eventually the scheme of turning UTC into a constant
> offset form of TAI requires a leap hour lest our descendants find
> themselves having their midday meal at 18:00 local civil time. This
> sort of pushing the problem off onto our descendants implies that we
> really don't have the right solution, just one that salves some needs
> now.

But civil time already has leap hours (positive and negative)
jumping around most parts of the globe twice a year. Furthermore,
about half of the year I have my "midday" meal at about 20:00 UTC,
and the other half I have it at 19:00 UTC. And when I travel, my
"midday" meal time often shifts to some other UTC time. Oh, sure,
the locals refer to the time as "noon" or "12:00", but that is not
what my watch (which is set to UTC) says. It is also very unusual for
it to be what my sundial would say (if I happened to bring it with me).

Trying to tie civil time to "mean solar noon" is merely a historical
convention. While global civil time standards have been been
fairly consistent in using this technique (even if there were
sometimes competing definitions for which meridian to use), it is
not a fundamental requirement of civil time. There are very few
locations on earth which use unadulterated UTC as their time base
(not even Great Britain, ignoring the distinction between GMT and
UTC, because about half the year they are on BST.) The requirements
of civil time are very forgiving --- if local solar noon is within a
couple of hours (sometimes more) of "clock noon", that appears to be
good enough for civil use (based on observation of current practice),
and offset-from-time-standard is controlled by political whim, which
means that current mechanisms are more than amply capable to make any
"leap hour" adjustments when such adjustments are felt to be necessary.


Can't we declare civil time a non-issue for now? I think both
UTC and TAI are significantly more-than-adequate for its meager
requirements (by precision time metrics). I know that plain
TAI is "not acceptable" to the astronomical community, who is an
important consumer of precision time, and that UTC (because it
is an approximation of UT1) "is acceptable", but that's about it.
Is there another community of time consumers for which UTC is better
than TAI? (Okay, "astronavigators", but unless one of them speaks
up about special needs I'll pretend like they are a subgroup of the
"astronomical community".) Is there a more useful time reference than
UT1 for the astronomical community? It seems like no one who is able
to answer these questions of mine ever feels like they are worthy
of an answer (or maybe I have just been too subtle in my asking),
but I think they are vitally important to the question of whether
(and if so how) our time standard should be changed. Yes, I am an
ignorant fool, but I can learn. Enlighten me.

                --Ken Pizzini
Received on Wed Jan 29 2003 - 01:16:35 PST