[fitsbits] Leap Second questionnaire

[Rob Seaman]

Peter Bunclark <psb at ast.cam.ac.uk> writes:

> Since leap seconds can be added or subtracted, then by extension leap 
> minutes could be negative as well as positive...

We don't have leap seconds because the Earth is spinning down.  We have
leap seconds because the Earth has *already* spun down since the reference
epoch at the dawn of the twentieth century.  Positive leap seconds would
continue to be necessary every year or so even if the Earth stopped
slowing entirely - for instance, under the Space 1999 scenario of no
more angular momentum being transferred to the lunar orbit.

To cause a negative leap second, not only would the Earth need to spin
up to overcome the current annual slowing trend, but it would have to
spin up to overcome the accumulated slowing over a century that has seen
a very consistent monotonic slowing trend.  I hesitate to speculate on
the cataclism necessary to accomplish this.

Obviously Peter's extension of this to a negative leap minute was just
a rhetorical device, but the folks in the time and frequency community
who are making decisions about the future of UTC appear to fail to see
the big picture of the spinning Earth through the thorny details of
Chebyshev polynomials and bureaucratic regulations.

Rob Seaman
NOAO