Re: [LEAPSECS] The real problem with leap seconds

From: Ed Davies <ls_at_EDAVIES.NILDRAM.CO.UK>
Date: Sat, 07 Jan 2006 14:48:22 +0000

Michael Sokolov wrote:
> Hello,
> I am a new entrant into the leap second debate and I have just written a
> paper in which I have outlined what I think is the real problem with UTC
> and leap seconds as they are currently implemented and a proposed
> solution. I have put the article on my web page:
> http://ivan.Harhan.ORG/~msokolov/articles/leapsecs.txt
> The short summary is that I believe the root problem is not the
> adjustments made to the civil time scale to match Earth's rotation, but
> the fact that UTC is not expressible as a real number. ....

UTC is expressible as a real number in just the same way that
Gregorian dates (with months with different lengths and leap
days) can be with the Julian calendar.

There's no difference in principle between converting from a
TAI time in seconds since some epoch to a UTC date/time in
days, hours, minutes, seconds and fractions of a second and
converting from an MJD day number to a Gregorian date in
years, months, days and fractions of a day.

(There's a small difference in practice in that the UTC to
TAI conversion requires a lookup table which is not known
very far into the future whereas the Gregorian calendar is
defined algorithmically for all time.)

You are sort of right, though, in that where computer systems
typically get screwed up is in trying to assign a number to
UTC seconds which is both a count since some epoch but also
able to be taken modulo 86 400 to give a day number. This is,
of course, impossible. What Markus Kuhn's UTS proposal was
about was trying to reach a standard compromise which worked
for such software - typically in cases where uniquely
labeling the times of events is more important than exact
interval determination.

Received on Sat Jan 07 2006 - 06:49:55 PST

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