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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