Risks of change to UTC

From: Rob Seaman <seaman_at_noao.edu>
Date: Mon, 16 Jan 2006 10:23:39 -0700

On Jan 15, 2006, at 1:07 PM, John Cowan wrote:

> There are a lot of systems, it seems, that assume DUT1 is bounded
> by either 0.9s or 1s. If leap seconds are turned off, then I'd
> expect that these will break and be replaced by systems that assume
> DUT1 is unbounded.

Ah. I see. You are focusing here on explicitly Y2K-like risks.
Those are indeed an issue, but I agree not a large one for most
constituencies. Only a minority (small minority, one would think) of
systems currently include any DUT1 correction at all - although these
will perhaps tend to be the most safety-critical applications. As
with Y2K, all systems have to be inventoried for potential risks, not
just ones you know about in advance.

That is, of course, one of the major issues for astronomers - we rely
on UTC providing a 0.9s approximation to UT1 and most of our systems
don't use DUT1. Even our high precision applications (in either
interval or universal time) don't tend to require conversions other
than as a preprocessing step. Remediating our systems for such a
fundamental change to UTC would involve much larger changes than Y2K
did - algorithms and data structures would have to change, not just
the width of some string fields and sprinkling some 1900's around.
(I know that oversimplifies Y2K - suspect virtually everybody on this
list was intimately involved with their organization's Y2K
remediation effort.) Also, standalone applications would have to
become network aware to have access to externally derived tables of

Astronomers might be unusual in needing to introduce DUT1 into our
systems (on a short schedule for a large expense) should Sauron win
and the nature of UTC change, but we wouldn't be alone. And as clock
time diverges further and further from solar time, more systems in
more communities (transportation, GIS, innumerable scientific
disciplines, what have you) would be revealed to need remediation.
That's where I was coming from.

Another issue is interoperability. There is the thought, perhaps,
that merely by deciding to cease issuing leap seconds that all clocks
on the planet will automatically converge on TAI (+ inane constant +
local offset). Some systems (like those in astronomy) will converge
on universal time. Would think it unwise to simply assume that no
significant risks will be revealed as the dual timescales diverge.
We all can likely agree that many deployed systems (of whatever
nature) are naively configured. Is this likely to change overnight?

Rob Seaman
Received on Mon Jan 16 2006 - 09:23:54 PST

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