Re: [LEAPSECS] Risks of change to UTC

From: James Maynard <>
Date: Sat, 21 Jan 2006 01:14:00 -0800

M. Warner Losh wrote:

> UTC works for navigation, but leap seconds pose problems for other
> users of time. Stating absolutely that UTC is not broken ignores
> these other users.

Those "other uses," for whom leap seconds pose a problem, should be
using a time scale that does not have leap seconds. They would be better
served, for example, by TAI.

UTC, with its leap seconds, evinces the fundamental problem that
calendar designers have faced through the ages: trying to devise
a compromise system that blends mutually incommensurable units.

For civil use, a calendar that counts days reaonably accurately is
appropriate. The Gregorian (New Style calendar) that the vast
majority of the planetary population uses does this. UTC copes with
the variable length of the mean solar day by inserting leap seconds
as needed. The role of the IERS in decreeing when leap seconds are
needed is similar to that of the Roman College of Pontifices who managed
the old Roman Republican calendar (before Julius Caesar's reform) by
decreeing, as needed, when to shorten the month of February and insert
the intercalary month of Mercurius.

Since we human creatures synch our cicadian rhythms and our daily
activities to periods of light and darkness, the day is a natural
unit of time for use in our calendars. Indeed, I know of no calendric
system that does not count days. Unfortunately, the day is ncommensurate
with the SI second, and the length of the day is changing.

If your primary need is for a time scale ithat counts SI seconds, with
no leap seconds to confuse the matter, then don't use UTC. Use a time
scale that counts SI seconds, such as TAI or GPS time. There's no point
to applying the mised radix Gregorian calendar system to such a time
scale, although you can do so if you wish. Count days of 86 400 SI
seconds each, or GPS weeks of 604 800 SI seconds, or just count SI seconds.

If, on the other hand, you need to count solar days, or mean solar days,
use a calendar and time scale that does so. In order to know which way
the earth is pointing, use UT1, or a compromise scale such as UTC that
  is kept reasonably close to UT1. For the vast majority of the
population of the planet, including celestial navigators, UTC is good
enough. If you want to know the direction the earth is pointing with
more precision, apply DUT1 corrections, or use other IERS products such
as Bulletin A.

There is no need to "fix" the time scale, UTC, that is used by the vast
majority of the planet's population to accommodate the very small
minority of precision time users who desire a time scale that has no
leap seconds. Let that minority use a time scale, such as TAI, that does
not have those messy leap seconds.

James Maynard
Salem, Oregon, USA
Received on Sat Jan 21 2006 - 01:14:21 PST

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