[ntp:questions] A Suggestion For Abolishing the Leap Second

Quadibloc jsavard at ecn.ab.ca
Wed Jun 6 23:22:31 UTC 2007

Rob van der Putten wrote:
> jlevine wrote:

> >    Yes, this idea was proposed some time ago, and it is currently
> > being
> > pushed pretty hard by the folks who need to plan for going to Mars.
> > Some
> > version of this idea will probably be adopted if/when space travel
> > becomes
> > more common. However, the idea that the rotating geoid (which is the
> > basis for the current SI defintion) is the center of the universe will
> > not
> > be easy to overcome.
> I was at high school in the 70's. At that time the definition of a
> second wasn't linked to the earth's rotation at all.
> I still have a list of SI units somewhere, but I can't find find it
> right now. However, I remember it having something to do with caesium
> and a number of periods.

Yes, this is quite right. However, while the second is no longer
defined in terms of a fraction of the tropical year in 1900, the
Earth's rotation still factors in to this in a more subtle way.

You see, the Earth is in *motion*. And the SI second is defined (in
practice, within the framework of UTC) as so many vibrations of a
cesium atom...*sitting on the Earth*. So what was being referred to in
what you are quoting is _not_ time being defined in terms of the
Earth's motion, instead of being atomic time (the poster works for
NIST, and has authored several papers on the atomic time scale) but
the fact that our current time scale doesn't include *relativistic
corrections* for the Earth's motion.

John Savard

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