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