[LEAPSECS] LEAPSECS] CCTF reported to CIPM last month and it's interesting!

[Seaman, Robert Lewis - (rseaman)]

Thanks for the link. But of course we’re not done here. We’ve barely started. Solar time is implicit in many engineering requirements across society. Pretending otherwise doesn’t make requirements go away.

On the other hand, for the use cases for which purely atomic time suffices, TAI was already available, and TI would already have been in use if the conclusions of the 2003 Torino meeting had been adopted.

I’m sure I’ll be long gone, but I predict the need for significant new infrastructure for solar timekeeping will appear in slide decks like these in decades and centuries hence. Leap seconds themselves were always a red herring. All that’s happened here is that the lab-coated acolytes of atomic time have succeeded in destroying the dictionary meaning of Universal Time.

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona

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On 12/1/25, 7:37 AM, "LEAPSECS" wrote:

External Email

https://www.bipm.org/documents/20126/280440045/11.+NMI+directors%2BMS+meeting-oct2025-CCTF+presentation-V5/b620db0a-bd29-2692-ebe9-83cf4ab7a0a2<https://www.bipm.org/documents/20126/280440045/11.+NMI+directors%2BMS+meeting-oct2025-CCTF+presentation-V5/b620db0a-bd29-2692-ebe9-83cf4ab7a0a2>

Optical second to page 33, leapsecond from there to p58, then lunar time.

The proposed CGPM resolution (pg. 58) is 1h DUT1 tolerance from May 20 2027.

They hold the door open to 2028, and must decide before jan 13th
where the CGPM convocation goes out. No reason given for why 2028
might be preferable.

Everybody (cited) wants "as soon as possible".

I note the uncertaintely in ER modelling:

The summary plot on pg, 50&57 show that the probability of a negative
leap-second in 2029 is already more than 10%, even assuming the
Director uses his discretion to delay it as long as possible.

And the "spaghetti" plot on pg. 49 shows TAI-UT1 from 36s…39s
already in 2030, and more than 32s…43 in 2035.

That can be fairly and precisly be summarized as "We have NO idea what
goes on with Earth Rotation" :-)

I guess we're done here ?

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