Re: [LEAPSECS] how posterity will measure time

From: Rob Seaman <seaman_at_NOAO.EDU>
Date: Mon, 4 Dec 2006 18:57:42 -0700

On Dec 4, 2006, at 4:27 PM, Ed Davies wrote:

> Do you really mean UTC here?

Well, I mean any of the various approximations of Universal Time as a
synonym for Greenwich Mean Time. As continental drift becomes
important, the job gets harder. (But then, to return to the original
topic, PHK and I would rely on continental drift to dispose of
nuclear waste.)

> I can see that an amateur with a
> Celestron could recover UT (for some flavour of UT, I'm not sure
> which - UT0?, then presumably UT1 after traveling around a bit)
> but where does the delta T come from to get UTC?

 From a knowledge of a (useful) policy for issuing leap jumps. If we
stick with individual leap seconds, we'll be within +/- 0.9s. Good
enough for government work – considering we're assuming that multiple
governments will have toppled in the mean time. More to the point,
good enough for recovering time series for astronomical and planetary
science work. etc.

> Actually, assuming somebody remembered to make a note of
> TAI-UTC before forgetting to put a shilling in the meter for
> the atomic clock TAI is exactly as recoverable as UTC in the
> short term when it's possible to work out the number of leap
> seconds which would have been inserted or removed.

Well, sure, I'm willing to reboot TAI from UTC (w/ leap seconds) –
kinda makes my tediously familiar case. Ditch leap seconds for the
nonsensical notion of leap hours, however, and we'd be in real
trouble vis-a-vis scientific opportunities in our post-apocalypse
scenario. Hoo-boy! Watch out!

> Longer term it would be harder, of course, but why would that matter?

I was just taking the opportunity to stay on message, of course. The
underlying point is that interval time and time-of-day are entirely
distinct concepts. My position, of course, is that civil time should
remain time-of-day. Judah Levine and David Mills have already solved
our problems, of course:

        http://www.eecis.udel.edu/%7emills/database/papers/leapsecond.pdf

Rob
Received on Mon Dec 04 2006 - 18:45:19 PST

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