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

jlevine jlevine at boulder.nist.gov
Thu Jun 7 14:33:17 UTC 2007

> 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, that is true. But the numerical value -- the number of periods
constitute a "cesium" second was defined in the 1970s so that it would
match the previous astronomical definition of the length of the
The problem was that the length of the astronomical second that was
used in this definition was based on data that was almost a century
and the length of the day (and therefore the length of the
second) had increased during that century. As a result, the actual
astronomical second in the 70s was already longer than the assumed
value that was used to define the number of periods of the cesium
that would equal an "atomic" second. Therefore, leap seconds were
needed immediately, and they are also of the same sign for this

 Judah Levine
Time and Frequency Division
NIST Boulder

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