Re: [LEAPSECS] what time is it, legally?

From: Rob Seaman <seaman_at_NOAO.EDU>
Date: Tue, 12 Dec 2006 16:42:53 -0700

On Dec 12, 2006, at 1:57 PM, M. Warner Losh wrote:

> I view the same data differently. I see it as a progression:
>
> Local Solar time -> mean local solar time ->
> timezone as mean local time at one point used for many -> UTC
> -> ???
>
> Clearly, we're moving away from solar time and towards something else.

Only if you successfully make that last leap into the unknown.

Rather, clearly we've refined our understanding of solar time over
the last couple of centuries. As demonstrated previously, all
parties agree (even if they don't agree that they agree :) that
short of some "caves of steel" science fiction scenario, civil time
must mimic mean solar time closely. We disagree over the definition
of "closely", but it is better than one second per day unless one
chooses to pretend that our "customers" that is, all the citizens
of all the countries of the world would suffer a leap hour every
decade (365 x 10 > 3600s). Consider that this one second (or much
tighter) tolerance is almost two orders of magnitude smaller than the
annual variation in the length of the apparent solar day.

 From my point of view, "closely mimic" should be regarded as "is"
that is, as a mathematical identity, not just a boundary condition to
be met by forcing equality once every millennium. On the other hand,
the precision timekeepers who proposed the absurd leap hour proposal
apparently deem a few milliseconds per day secular trend as being
tolerable slop. (Rather strange coming from technologists who dote
on nanoseconds.) My position is:

        Civil Time == Mean Solar Time (i.e., "time-of-day")

The time lords assert:

        Civil Time = Mean Solar Time + epsilon ("something masquerading as
time-of-day")

Which begs the question of what Civil Time is, if it ain't MST but
must be approximated so.

The mere fact of the ALHP arising among those who clearly loathe leap
seconds is a tacit admission that mean solar time rules now and
will continue to do so in the future. The leap seconds don't get
legislated out of existence, after all, they are merely embargoed for
several centuries. The proponents of the ALHP are not suggesting a
way to escape from this constraint, rather they are acknowledging it
precisely by the form of their Machiavellian non-proposal.

One might suggest that if 1) the ALHP were taken off the table such
that we didn't have to keep batting the smelly thing away, and 2) its
proponents would deign to participate in a dialog, then 3) progress
might actually be made on solving the real problem of conveying BOTH
interval time AND time-of-day to the precision time users (i.e.,
"people") of the world.

It isn't revolutionary to suggest that you look before you leap
(http://en.wikipedia.org/wiki/Precautionary_principle).

Rob Seaman
NOAO
Received on Tue Dec 12 2006 - 15:43:13 PST

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