Re: [LEAPSECS] trading amplitude for scheduling

From: Rob Seaman <seaman_at_NOAO.EDU>
Date: Fri, 4 Aug 2006 08:58:32 -0700

Hi Tom,

> Careful not to confuse rate with acceleration and
> propagate a common misconception that leap
> seconds are due to an acceleration/deceleration
> effect (as in "leap seconds are due to the earth
> slowing down").
> In fact, leap seconds are simply due to the earth
> being slow. How it got to be "slow" and whether
> it is "slowing" are another issue.
> There are valid scenarios where the earth could be
> speeding up and yet we would continue to have leap
> seconds -- because the earth is still slow (compared
> to the SI second).
> Rate is not the same as acceleration; leap seconds
> are directly due to a rate mismatch, and only indirectly
> due to deceleration.

You appear to be addressing me, which suggests that my message (half
of it, anyway) didn't parse for you into the exact same statement as
yours that I was attempting to make. See various messages of mine
over the years, decades and centuries this list has been in
existence. See also discussion at

We have two clocks. Their rates are already different (and will
diverge further whatever the ITU does). Therefore, one of the clocks
must be reset occasionally. Over timescales of interest to anybody
attempting to understand the Earth and its place in the cosmos,
however, the fact that we have a big dang moon is not negligible.

You say "directly" and "indirectly". I might choose "proximally" and
"ultimately". After all, the length of the second was supposed to
scale to the rotation of the Earth, just as the length of the meter
was supposed to scale to the size of the Earth. The fact that we
live on a charmingly wobbly planet is not something our policymakers
should be encouraged to attempt to ignore.

Received on Fri Aug 04 2006 - 08:59:21 PDT

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