Re: [LEAPSECS] GMT -> UTC in Australia

From: Rob Seaman <>
Date: Thu, 24 Feb 2005 10:54:05 -0700

John Cowan says:

> Secular changes in time zones (if by "time zone" you mean "LCT - UTC",
> as I suppose) are something we already know how to handle, as they
> must be taken into account when determining historical UTC/GMT to LCT
> conversion. Indeed, some countries jigger the dates of their
> semiannual time changes annually, which is also a secular change in a
> small way.
> In addition, there is no reason why all the world's time zones must
> change in a synchronized way; ad hoc changes, as and when the problems
> become irritating, will be sufficient. Some jurisdictions might
> choose to change by half-hour offsets in only three centuries.

"Ad hoc" is not a synonym for secular. I'm pleased to see someone
other than the astronomers in this conversation using the word secular,
but there continues to be a fundamental confusion of Daylight Saving
clock adjustments (periodic) with the silly notion of leap hours
(fundamentally secular).

No reasonable standard can be based on constraining the behavior of our
descendants 600 years hence. The only thing that emasculating UTC will
accomplish is to allow sloppy system architects to continue to ignore
the true requirements for choosing a time scale - with no guarantee
that they'll get the requirement to handle a large and growing DUT1
right, any more than they appear to have gotten the requirement to
handle leap seconds right. If a technical project requires unsegmented
time, the architects should choose some flavor of TAI - GPS is a good
example. If a technical project requires a clock slaved to the Earth's
rotation, the architects should choose some flavor of UT. And if a
project requires both, UTC is an excellent choice - it delivers TAI
with a precision two orders of magnitude higher than its delivery of
UT1. How about basing our discussions - and the IAU/IERS/BIPM/ITU-R
deliberations - on the technical details of delivering *both* time
signals with more complete worldwide coverage and a significantly
improved level of precision and accuracy? If you want to buy the
astronomers' support, that is surely the best way to do it.

Meanwhile, my readings of the requirements for civil time are that the
world's clocks should remain fundamentally rooted in time-of-day, not
atomic time. Your interpretation may differ - I ain't got a problem
with differences of opinion. What I have a problem with is the
arrogant behavior of minor league bureaucrats who are seeking to
effectuate a fundamental change to the philosophy of civil time without
even considering consulting the civilians themselves.

You can bet that the Australian legislators who are pushing this bill
were given the impression that UTC is just a modern name for GMT - with
the sub-text that Australia doesn't want to appear old-fashioned. You
can bet that the so-called time lords didn't think to confuse the issue
by droning on about the likely unhappy future of leap seconds.

The only possible explanation for continuing to call civil time
"Coordinated Universal Time" in the absence of leap seconds is that the
public are being misled in order to sneak through this silly leap hour
proposal. Whether any one of us supports the proposal or not, we
should be able to reach agreement that misinformation is not the
appropriate way to make public policy.

Gedanken experiment: Call the new system of time resulting from the
leap hour proposal "International Time", TI for short. Walk through
the front door of the world's parliaments and legislatures and attempt
to sell TI as a high priority proposal. What would be the likely

Rob Seaman
National Optical Astronomy Observatory
Received on Thu Feb 24 2005 - 09:54:44 PST

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