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

jlevine jlevine at boulder.nist.gov
Sat Jun 2 20:49:15 UTC 2007


> >   In the first place, the unit of frequency plays a central role in
> > precision
> > measurements and fundamental constants -- much more fundamental than
> > the unit of time. If the time services distributed a non-SI frequency
> > then
> > all frequency calibrations would become much more difficult and
> > ambiguous.
> I can understand that, and I do not advocate that any different
> frequency be distributed.

    The difficulty is that timing laboratories do not distribute
frequency as distinct from time.
Precision frequency comparisons are done by measuring the evolution of
the time difference
(which is often expressed as a fraction of a cycle for the highest-
precision comparisons)
between a device under test and a calibration source. Thus, changing
the length of the second
effectively changes the frequency that is being transmitted. (Pretty
much all time distribution
systems use a single oscillator to generate both the carrier and the
time code.) As I mentioned in my previous note, this was one of the
reasons that a method similar to what you are proposing
was abandoned in the early 1970s. For what it is worth, my personal
opinion is that changing the length of a second in any manner would be
completely unacceptable to the frequency community and it simply won't
be accepted.

> This means that the discrepancy between the modified
> UTC and mean solar time would be allowed to be somewhat larger than
> 0.9 seconds.

    This would not be a trivial change. Broadcast services (NIST radio
station WWVB,
for example) transmit the current dUT1 parameter as specified by the
Telecommunications Union (ITU). The format does not allow a value
greater than
0.9 seconds. If this difference is allowed to exceed +/- 0.9 s then
something has to
change. Either the station would stop transmitting the dUT1 parameter,
or it would be
transmitted modulo 1 second or something else. None of these changes
is impossible, but they could not be implemented without discussons by
the appropriate
group in the ITU. In fact, the leap second question is already being
discussed there.
Although no formal decision has been reached, my guess is that nothing
will change and
the current system will continue as is. However, this is just my
private guess.

Judah Levine
Time and Frequency Division
NIST Boulder

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