Re: [LEAPSECS] trading amplitude for scheduling

From: Rob Seaman <>
Date: Fri, 4 Aug 2006 14:06:33 -0700

Tom Van Baak says:

> you could say the SI second was defined
> a bit too fast. The error bars on Essen's 9192631770 Hz
> cesium calibration were rather large and he used an old
> epoch for the ET second.

Hmmm - I see a gedankenexperiment here. (Maybe I'll
judge that category of science fair project some year, rather
than middle school physical sciences. Would be a blast :-)

Posit the absence of the Moon - or at least of secular
deceleration, tidal or otherwise, of the Earth's rotation.


Posit that Louis Essen (
had successfully matched his calibration to the actual length
of the mean solar day.

First result - interval time (the SI second) would remain in
step with time-of-day (mean solar time).

> Leap seconds occur irregularly because the
> rate of rotation is irregular over the relatively short time
> span of months to years. Even if there were no secular
> deceleration over the time scale of centuries -- we would
> still have leap seconds; and they would continue to be
> irregular.

Second result - the Earth's rotational foibles would remain
manifest in a natural limit of precision to Essen's calibration.

The third figure from
shows just such seasonal and decadal variations with something
like +/- 1.5 ms excursions. These are far from random, and there
may be long term effects amounting to several seconds (the first
figure from Steve's page suggests +/- 5 sec over millennial time
scales), but - there is some hope of establishing a natural scale
for a leap "jump" that is tied to geophysics, not to Babylonian
sexigesimal numeracy, whether seconds OR hours.

Third result - even in the absence of lunar braking, leap jumps
(or equivalent clock adjustments) would remain necessary.

Received on Fri Aug 04 2006 - 14:06:49 PDT

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