[LEAPSECS] What's the point?

Rob Seaman seaman at noao.edu
Mon Feb 14 16:28:52 EST 2011

Tony Finch wrote:

> Rob frequently argues that we can't use a pure atomic timescale as the basis of civil time because of the quadratically increasing offset betwee UT1 and TAI.

Well no, I don't think I've ever made such an argument. It is a question of rates, not offsets. And the two clocks would continue to be mismatched in rate even if the Earth's length-of-day remained fixed from here on out.

> The counter-argument is mainly to point out that the offset is negligible from the point of view of the majority of people.

The differing rates are not negligible and the resulting "offsets" (clock setting errors) will continue to accumulate whether or not a quadratic apocalypse is looming.

It is simply true that TAI counts out SI-seconds, but UTC tracks synodic days. They are two different clocks. It is this silly insistence on treating them as the same thing that is generating all the trouble.

The "counter-argument" asserts that synodic days are negligible. Many here disagree with this naive and self-serving assertion.

> It won't become uncomfortable until about a thousand years in the future,

Rather, it will immediately break large quantities of expensive astronomical systems and software. Not your problem? It is mine.

> by which time leap seconds will be stretched to breaking point.

Here is where you are reinserting an assertion about the quadratic end-of-days. Leap seconds are at least as adaptable as anything else suggested here. But again - the ITU draft recommends *nothing*. It makes no assertions of its own about what mechanism will eventually bleed off the leap-second-equivalents. The ITU simply wants to dump the problem on later generations (and current astronomers).

For more than 10 years we have had no option but to continue to try to stop the ITU from making a colossally stupid decision. There is no deadline. Table the attempt to redefine UTC. If you need to revise TAI or define a new leap-less timescale, just go ahead and do it. Meanwhile we can start discussing the proper engineering of the next-generation timekeeping standards in coordination with all the stakeholders, not just this tiny in-group.

> Furthermore using timezones to keep civil time in sync with the sun leads to simpler software and it will work for over ten thousand years.

No. Breaking timezones on top of breaking UTC with the apparent motivation of allowing TAI to be "suppressed" is bad on top of bad on top of bad.

Understand the problem, engineer a solution, skip the politics and drama.

We should take our time and get it right.

Rob Seaman
National Optical Astronomy Observatory

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