Re: [LEAPSECS] Where the responsibility lies

From: Poul-Henning Kamp <phk_at_phk.freebsd.dk>
Date: Tue, 03 Jan 2006 20:32:08 +0100

In message <114FC98B-11B3-47AE-A273-FF57D2DAC7DF_at_NOAO.EDU>, Rob Seaman writes:
>John Hawkinson replies:
>
>I think PHK has demonstrated the ability (and willingness :-) to hold
>up his own end of an argument. Should we ever find ourselves at the
>same conference, I'll buy him a beer in anticipation of a rousing
>discussion.

I'll be happy to bring booze as well :-)

>There are several issues confounded here. First, an untested
>assertion that eliminating leap seconds will simplify time handling.
>DUT1 looms large in astronomical software and one would have to be
>convinced that this is not an issue with other disciplines.

But it's exactly the fact that DUT1 already exists that bugs me.

If you already have to cope with DUT1 anyway, how much difference
can it possibly make if the definition says
         |DUT1| < .9
or
         |DUT1| < 10sec
or
         |DUT1| < 1 hour

If we can increase the tolerance to 10sec, IERS can give us the
leapseconds with 20 years notice and only the minority of computers
that survive longer than that would need to update the factory
installed table of leapseconds.

>Third, leap seconds are a mechanism to realize mean solar time in
>practice.

As would leap-hours (or jumping timezones) be. It's only a matter of
the tolerance we accept on DUT1.

As far as I know, less than 1% of people on this planet actually
have the sun straight south at 12:00 local time today and a quite
sizeable minority (a lot of China) lives perfectly happy with the
sun being further than 15 degrees from south at local 12:00.

It follows from this, that a proposal for a 1hour tolerance on
DUT1 is perfectly feasible without odd things happening to the
cows milk etc.

>The acknowledgment of a contingent need for
>leap hours shows that the authors of the ITU proposal understand this.

I think the leap hours is a political tool to make the proposal go
through without commiting anybody to anything for the next couple
of hundred of years.

>Fourth, the need for leap seconds is growing quadratically as the
>Earth continues to slow. We have no business making ad hoc policies
>based on the rarity of events that are becoming more frequent. The
>need for "leap hours" will grow just as rapidly - and much more
>dramatically. A solution that ignores real world constraints is no
>solution.

Uhm, no.

There are three orders of magnitude difference between a leap second
and a leap hour, and consequently the need for leap hours will grow
less rapidly than the need for leapseconds.

>In short, leap hours are - well - dumb. A proposal that relies on
>their use, naive.

Leap hours or leap seconds is only a matter of magnitude and
frequency and consequently both are equally na´ve.

Poul-Henning

--
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk_at_FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Received on Tue Jan 03 2006 - 11:43:11 PST

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