extracting leap second schedule

From: Zefram <zefram_at_fysh.org>
Date: Wed, 24 May 2006 14:27:12 +0100

I've written a Perl module that handles the conversion between TAI and
UTC. It's Time::UTC, available at <http://search.cpan.org/~zefram/>.
When asked about future times where it doesn't yet know the
leap second schedule, it automatically downloads and parses
<http://maia.usno.navy.mil/ser7/tai-utc.dat>. This works well if there's
a future leap second already scheduled, but otherwise there is a problem
in working out how far ahead the last TAI-UTC offset applies.

My code currently assumes that the file applies at least seven weeks into
the future. (The official notice is eight weeks, but I don't know how
quickly this file is updated, and the code has to work from a system
clock of unknown accuracy.) I'm uneasy about the whole principle of
relying on a file that hasn't been updated in possibly years to give
new information. It only works because I get the file from a very
official source that can be expected to provide fresh information.
I'd much prefer if the file had as its last line an explicit indicator
of the earliest time that another leap second could now be added.

Does anyone have any better ideas for how to atomatically determine the
limit of knowledge of TAI-UTC? I emailed the IERS in January and got
an acknowledgement of my question but no answer so far.

Amusingly, in the long run this will become a non-problem on its own.
In perhaps a century or so it will become unavoidable to schedule
more than one leap second ahead. That way the final time mentioned in
tai-utc.dat will always be in the future.

Received on Wed May 24 2006 - 08:37:58 PDT

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