[LEAPSECS] it's WP7A week in Geneva

Rob Seaman seaman at noao.edu
Tue Oct 6 02:36:00 EDT 2009

Sitting in a plenary session - will keep this short.

Executive summary: GPS is great stuff. Universal Time is also great
stuff. They are not the same great stuff.

M. Warner Losh wrote:

> Everybody that implements leap seconds in time keeping will

> automatically be correct if they were eliminated.

This has not been demonstrated to be correct. Some systems care about
mean solar time. You are asserting that A) astronomers don't matter,
and B) no other systems in the world care about Earth orientation to a
degree we need be concerned about.

> It would still work if leap seconds were scheduled out more than 6

> months in advance too.

No argument there! By all means increase the announcement horizon.

> Most people live their lives where the sun has an apparent error of

> tens or hundreds of minutes off.

I'll make my usual observation that this confuses periodic and secular
effects. See list archive.

> We're also putting off the problem. Given the quadratic

> acceleration of drift, one day we'll have to have a better system is

> synchronization to the earth's rotation is to remain viable.

The quadratic behavior applies no matter what. Embargoing leap
seconds does not make them go away. Unless we believe night can turn
into day, civil time must be synched to the Earth's rotation to match
some constraints. By all means let's debate the constraints. It is
not viable, however, to simply ignore the sun in the sky. As the
Earth clock slows (albeit thousands of years from now), it will become
obvious that we can't pretend atomic time and solar time are the same
thing. Why not admit this fact of life now?

The way to reach a robust consensus on what constitutes a "better
system" is to discover and debate the underlying requirements of the
system. Define the problem appropriately and the range of acceptable
solutions will take care of itself.


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