Re: [LEAPSECS] interoperability

From: M. Warner Losh <imp_at_BSDIMP.COM>
Date: Mon, 09 Jan 2006 00:36:30 -0700 (MST)

In message: <20060109070328.GE5921_at_ccil.org>
            John Cowan <cowan_at_CCIL.ORG> writes:
: > But how in practice is it envisaged that a scheme
: > for migrating time zones versus TAI would work, precisely?
:
: Straightforwardly. Each locality decides when and how to adjust both
: its offset from TAI and its seasonal transition function (if any),
: just as it does today. What we abandon is a universal time tightly
: synchronized to Earth rotation in favor of a universal time
: independent of earth rotation plus 400+ local civil times roughly
: synchronized to Earth rotation containing various glitches.

No matter what we do with leapseconds, there are still all those time
zones.

The problem with stopping leap seconds altogether is that the legal
definitions of time, although quite varied, are all about the same as
UTC as it exists today. They are close enough that most countries
have adopted UTC bureaucratically rather than legislatively. The
official time for the US, as published by the folks at NIST, is UTC.
The US law says mean solar time, as determined by the Secretary of
Commerce, who has delegated it to the Time and Frequency division of
NIST, who in turn use UTC. NIST could easily use a different schedule
for leap second insertion (it could have inserted the leap second in
civilian time at the end of any day it wanted to and still maintained
the mean solar time legal requirement). However, since UTC is a
recognized, international standard, the US went along and did its leap
second according to that standard. This is a explicit choice that
someone, somewhere had to make, even though it is arguably the best
choice to make (wouldn't want to be the odd man out in civil time,
think of the impact on business).

The combination of UTC approximating the legal time is so man nations,
as well as the need for international consensus among lots of parties
with divergent views for any changes to the current system is why
we'll likely not see significant changes any time soon. The best we
can hope for is that something will be done to change their
unpredictable nature given that we have good forcasting tools at our
disposal.

Warner
Received on Sun Jan 08 2006 - 23:38:04 PST