[fitsbits] leap second alert

[Rob Seaman]

We had an interesting inquiry that deserves a wider distribution.
An astronomer with a friend at the NIST forwarded this to an NOAO
staff member who forwarded it to me.  Now it's in your lap, too.

    > As you know, Coordinated Universal Time (UTC) is derived from cesium
    > clocks with the occasional addition of leap seconds. These leap seconds
    > guarantee that the magnitude of UTC-UT1 does not exceed 1 s.
    > 
    > Managing leap seconds is an administrative headache, and there have
    > been proposals for some time to abandon using them. If this were done,
    > the difference between UTC and UT1 would grow without bound. Currently,
    > the rate of divergence is about 1 minute per century, and this rate is
    > projected to increase as the Earth continues to slow down.
    > 
    > Assuming this were done, would the lives of astronomers be made more
    > difficult?  If astronomers have to incorporate a UT1 correction in any
    > case, does it matter how big it is? If they currently use this
    > correction, how accurately do they need to know it?
    > 
    > Thanks for your assistance.
    > 
    > Judah Levine

Our reply was basically that most ground-based astronomers and most
ground-based observatories' "utility" chores (like pointing the telescopes)
have no real need for high precision timing information - but that the
small fraction that do may have very stringent needs indeed.  We also
suggested that they should talk to the nice folks at the USNO and that
this obviously rises to the level of requiring an IAU decision.

The question is also phrased in a vague enough fashion that it isn't clear
precisely what they are suggesting.  Clearly, astronomers can't be the only
ones with a requirement for an "inertial" time system.  (One might imagine
that a large number of inobvious terrestrial applications rely on leap
seconds implicitly or explicitly.)

Whatever they are suggesting we still will require continuing support for
a time system that doesn't drift monotonically with respect to the sky.

The explicit question in the reply was:

>> What is the point of this inquiry?  Is this some time keeping authority
>> wondering the equivalent of Kodak's request every couple of years about
>> what emulsions astronomers may actually be using?

And here is what I suggest you all ponder:

    > From jlevine at india.colorado.edu Mon Nov 22 14:56:10 1999
    > Subject: leap seconds
    >
    > Hello,
    >
    >> What is the point of this inquiry?  Is this some time keeping
    >> authority wondering ...
    >
    > Thank you for your comments. The Time and Frequency community
    > regards leap seconds as a nuisance and a bother, and there is an
    > increasingly strong push to abolish them. This would cause UT1-UTC
    > to grow without bound. Time and frequency folks generally don't
    > care about UT1, but I thought that this might bother astronomers.
    > If it does not, then so much the better. On the other hand, if there
    > is some application that would be seriously affected by this change
    > then it would be useful to know about it now before the move to
    > abolish leap seconds gains something approaching ustoppable momentum.
    >
    > Judah Levine
    > Time and Frequency Division
    > NIST Boulder

So - any comments on specific FITS leap second requirements?

Any more general astronomical concerns should be directed toward raising
an immovable object in the path of that unstoppable momentum.  I'm a bit
concerned at the rather unofficial channels that this official of the
"Time and Frequency community" decided were sufficient to consult.
(After all, we were the original time and frequency community...)

Rob

-- 
seaman at noao.edu, http://iraf.noao.edu/~seaman
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