[LEAPSECS] (no subject)

Rob Seaman seaman at noao.edu
Sat Dec 20 13:45:49 EST 2008

M. Warner Losh wrote:

> Leap-seconds, as implement, are unworkable.

If so, there are worlds of possibilities short of the vain attempt to
eradicate them entirely.

> You can see long messages from me in the past enumerating the

> reasons relating to systems, especially systems disconnected from

> the internet...

Systems (still unenumerated) that require real-time access to actual
"UT" (a flavor of GMT), will have this same exact issue, but the ITU
proposal does nothing to plan for a replacement. Rather, it demands
that the current DUT1 mechanism be abandoned.

As other long messages point out, it is simply not true that most or
many or more than a very small fraction of systems need real-time leap
second updates.

Ultimately, even non-realtime systems will suffer as vast numbers of
embargoed leap seconds pile up. These will have to be released
eventually. What is the plan for doing so? Include that plan in any
proposal to change the status quo.

> Leap-seconds, the concept, have a limited shelf life. Maybe only a

> few thousands years. So there's nothing really to preserve. One day

> they must be abandoned.

The current standard is workable for at least hundreds of years. What
is the hurry to vote on this issue without reaching consensus first?
Could it be that the proponents don't believe the current proposal is
coherent enough to win over converts outside of their own special
interests? Whatever action might be taken, plan the evolving standard
fully before taking it.

> As soon as we fixed the length of a second based on atomic behavior

> rather than as 1/86400th of a mean solar day, we really abandoned time

> based on mean solar time.

Civil time is and will remain a flavor of mean solar time. If you
believe otherwise, muster arguments for how this assertion fails to be
true. It is a basic requirement of any replacement that the clock not
drift willy-nilly, but rather be accommodated by some well thought out
plan. It isn't the astronomers on this list who have been unwilling
to consider alternative proposals.

> Leap seconds are at best a hack to paper over this fundamental

> decision.

No - inappropriate attempts to apply interval timescales to civil
timekeeping are the real kludge. The issue remains the conflation of
the two distinct concepts of the SI second with the civil second
(1/86400 of a day). This is a naive attempt at redefining the
fundamental concept of the day.

Even if we evolve into mole-people living underground and losing the
power of sight, an intelligent species will never abandon civil
timekeeping based on mean solar time. Diurnal rhythms abound
throughout our society and its infrastructure. All the confusion
about zero point shifts is a red herring. The issue is that the mean
solar rate has to be maintained. It is a strange position for
precision timekeepers to take that a residual rate of milliseconds per
day should be regarded as negligible. We can cheat the sun for a
while - but only for a while.

There are two kinds of time, interval and earth orientation. Whatever
the ITU rules at some future meeting these must be kept straight - and
civil timekeeping depends much more on earth orientation than on
interval timing. If there are problems with interval timekeeping,
then civil time is not the right place to address them. Separate the
two sets of issues and the proper solution(s) will become easier to
design and deploy.


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