Re: [LEAPSECS] trading amplitude for scheduling

From: Rob Seaman <seaman_at_noao.edu>
Date: Fri, 4 Aug 2006 10:01:55 -0700

John Cowan wrote:

> 1) We have leap seconds because the Earth rotates more slowly
> than once every 86,400 SI seconds.
>
> 2) Leap seconds will become more frequent in the future because
> the Earth is decelerating.
>
> 3) Leap seconds occur irregularly because the Earth's deceleration
> is not constant and in fact changes unpredictably.
>
> Right?

Right. One might, however, choose to restate #1:

> 1) We have leap seconds because the SI second is shorter
> than 1/86,400 of a mean solar day.

The SI second rather matches the length of the day c. 1820.
(See http://www.ucolick.org/~sla/leapsecs/timescales.html)

And in a post-leap hour world, one could also say:

> 1a) We have leap hours because the Earth rotates more slowly
> than once every 24 SI hours, or
>
> 1b) We have leap hours because the SI hour is shorter
> than 1/24 of a mean solar day.
>
> 2) Leap hours will become more frequent in the future because
> the Earth is decelerating.
>
> 3) Leap hours occur irregularly because the Earth's deceleration
> is not constant and in fact changes unpredictably.

Presumably one could identify 1 SI hour as 3,600 SI seconds.
The problem with this is that an hour has always meant 1/24 of
a day, so one is really redefining the concept of "dayness".
And a day has always meant a subdivision of the calendar, so
one is redefining the calendar.

If an Earth day has nothing to do with the rotation of the Earth,
why should a Mars day have anything whatsoever to do with
Mars?

Rob
NOAO
Received on Fri Aug 04 2006 - 10:02:30 PDT

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