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
