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Re: [Ntp] changes in length of day, was Re: New Version Notification for draft-gruessing-ntp-ntpv5-requirements-03.txt

Tony Finch <dot@dotat.at> Tue, 26 October 2021 21:13 UTC

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Date: Tue, 26 Oct 2021 22:13:50 +0100
From: Tony Finch <dot@dotat.at>
To: kristof.teichel@ptb.de
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Subject: Re: [Ntp] changes in length of day, was Re: New Version Notification for draft-gruessing-ntp-ntpv5-requirements-03.txt
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kristof.teichel@ptb.de <kristof.teichel@ptb.de> wrote:

> Yeah, sorry, I forgot to add that these weren't idle fears. The earth
> rotation does appear to be speeding up right now, it is just a bit
> unclear whether or not it will *keep* doing it long enough for that
> negative leap second to become necessary.

The best way I know of to get a rough indication of when the next leap
second might happen is using IERS Bulletin A. It contains predictions of
DUT1 for the next year, plus a simple equation that can be used for longer
term projections. It's basically a linear multiple of the current length
of day (less 24*60*60 seconds) plus some seasonal adjustment terms that
aren't relevant to the current discussion.

In the last few years, the Bulletin A estimated long-term LoD was longest
in June 2016 at +1470 µs. It dropped fairly steadily, eventually becoming
less than 86400 seconds in November last year. It stopped getting shorter
in May and is now gradually getting longer, but the LoD is still 220 µs
less than 24*60*60 s, which suggests there might be a negative leap second
in about 8 years, if things don't change, though they certainly will
change.

Here's some output from a program I wrote:

https://github.com/fanf2/bulletin-a

2020-01-02 -> 2023-06-30 (+) UT1-UTC -0.594 ± 0.053 s (lod +320 µs)
2020-01-09 -> 2023-06-30 (+) UT1-UTC -0.582 ± 0.053 s (lod +310 µs)
2020-01-16 -> 2023-06-30 (+) UT1-UTC -0.563 ± 0.053 s (lod +290 µs)
2020-01-23 -> 2023-06-30 (+) UT1-UTC -0.555 ± 0.053 s (lod +280 µs)
2020-01-30 -> 2023-12-31 (+) UT1-UTC -0.569 ± 0.058 s (lod +270 µs)
2020-02-06 -> 2024-06-30 (+) UT1-UTC -0.612 ± 0.063 s (lod +250 µs)
2020-02-13 -> 2024-06-30 (+) UT1-UTC -0.596 ± 0.063 s (lod +240 µs)
2020-02-20 -> 2024-06-30 (+) UT1-UTC -0.581 ± 0.063 s (lod +230 µs)
2020-02-27 -> 2024-06-30 (+) UT1-UTC -0.567 ± 0.063 s (lod +220 µs)
2020-03-05 -> 2024-06-30 (+) UT1-UTC -0.554 ± 0.063 s (lod +210 µs)
2020-03-12 -> 2024-06-30 (+) UT1-UTC -0.540 ± 0.062 s (lod +200 µs)
2020-03-19 -> 2025-06-30 (+) UT1-UTC -0.591 ± 0.073 s (lod +190 µs)
2020-03-26 -> 2025-06-30 (+) UT1-UTC -0.569 ± 0.073 s (lod +180 µs)
2020-04-02 -> 2025-06-30 (+) UT1-UTC -0.570 ± 0.072 s (lod +180 µs)
2020-04-09 -> 2025-06-30 (+) UT1-UTC -0.552 ± 0.072 s (lod +170 µs)
2020-04-16 -> 2025-06-30 (+) UT1-UTC -0.551 ± 0.072 s (lod +170 µs)
2020-04-23 -> 2025-06-30 (+) UT1-UTC -0.530 ± 0.072 s (lod +160 µs)
2020-04-30 -> 2026-06-30 (+) UT1-UTC -0.564 ± 0.082 s (lod +150 µs)
2020-05-07 -> 2026-06-30 (+) UT1-UTC -0.569 ± 0.082 s (lod +150 µs)
2020-05-14 -> 2026-06-30 (+) UT1-UTC -0.574 ± 0.081 s (lod +150 µs)
2020-05-21 -> 2026-06-30 (+) UT1-UTC -0.554 ± 0.081 s (lod +140 µs)
2020-05-28 -> 2026-06-30 (+) UT1-UTC -0.556 ± 0.081 s (lod +140 µs)
2020-06-04 -> 2026-06-30 (+) UT1-UTC -0.556 ± 0.081 s (lod +140 µs)
2020-06-11 -> 2026-06-30 (+) UT1-UTC -0.553 ± 0.081 s (lod +140 µs)
2020-06-18 -> 2026-06-30 (+) UT1-UTC -0.528 ± 0.080 s (lod +130 µs)
2020-06-25 -> 2026-06-30 (+) UT1-UTC -0.526 ± 0.080 s (lod +130 µs)
2020-07-02 -> 2026-06-30 (+) UT1-UTC -0.520 ± 0.080 s (lod +130 µs)
2020-07-09 -> 2027-06-30 (+) UT1-UTC -0.539 ± 0.090 s (lod +120 µs)
2020-07-16 -> 2028-06-30 (+) UT1-UTC -0.549 ± 0.099 s (lod +110 µs)
2020-07-23 -> 2028-06-30 (+) UT1-UTC -0.547 ± 0.099 s (lod +110 µs)
2020-07-30 -> 2028-06-30 (+) UT1-UTC -0.520 ± 0.099 s (lod +100 µs)
2020-08-06 -> 2028-06-30 (+) UT1-UTC -0.522 ± 0.098 s (lod +100 µs)
2020-08-13 -> 2029-06-30 (+) UT1-UTC -0.523 ± 0.107 s (lod +90 µs)
2020-08-20 -> 2029-06-30 (+) UT1-UTC -0.518 ± 0.107 s (lod +90 µs)
2020-08-27 -> 2030-06-30 (+) UT1-UTC -0.508 ± 0.116 s (lod +80 µs)
2020-09-03 -> 2031-06-30 (+) UT1-UTC -0.493 ± 0.125 s (lod +70 µs)
2020-09-10 -> 2031-06-30 (+) UT1-UTC -0.489 ± 0.124 s (lod +70 µs)
2020-09-17 -> 2032-06-30 (+) UT1-UTC -0.470 ± 0.133 s (lod +60 µs)
2020-09-24 -> 2033-06-30 (+) UT1-UTC -0.487 ± 0.141 s (lod +60 µs)
2020-10-01 -> 2034-06-30 (+) UT1-UTC -0.452 ± 0.149 s (lod +50 µs)
2020-10-08 -> 2037-06-30 (+) UT1-UTC -0.441 ± 0.173 s (lod +40 µs)
2020-10-15 -> 2040-06-30 (+) UT1-UTC -0.412 ± 0.195 s (lod +30 µs)
2020-10-22 -> 2045-06-30 (+) UT1-UTC -0.377 ± 0.231 s (lod +20 µs)
2020-10-29 -> 2045-06-30 (+) UT1-UTC -0.376 ± 0.231 s (lod +20 µs)
2020-11-05 -> 2054-06-30 (+) UT1-UTC -0.318 ± 0.292 s (lod +10 µs)
2020-11-12 -> ????-??-?? (?)
2020-11-19 -> ????-??-?? (?)
2020-11-26 -> 2158-12-31 (-) UT1-UTC +0.843 ± 0.841 s (lod -20 µs)
2020-12-03 -> 2073-12-31 (-) UT1-UTC +0.416 ± 0.411 s (lod -30 µs)
2020-12-10 -> 2053-12-31 (-) UT1-UTC +0.317 ± 0.288 s (lod -40 µs)
2020-12-17 -> 2048-12-31 (-) UT1-UTC +0.347 ± 0.255 s (lod -50 µs)
2020-12-24 -> 2042-12-31 (-) UT1-UTC +0.400 ± 0.212 s (lod -70 µs)
2020-12-31 -> 2040-12-31 (-) UT1-UTC +0.422 ± 0.198 s (lod -80 µs)
2021-01-07 -> 2037-12-31 (-) UT1-UTC +0.459 ± 0.175 s (lod -100 µs)
2021-01-14 -> 2035-12-31 (-) UT1-UTC +0.443 ± 0.159 s (lod -110 µs)
2021-01-21 -> 2033-12-31 (-) UT1-UTC +0.458 ± 0.143 s (lod -130 µs)
2021-01-28 -> 2033-12-31 (-) UT1-UTC +0.503 ± 0.142 s (lod -140 µs)
2021-02-04 -> 2031-12-31 (-) UT1-UTC +0.476 ± 0.125 s (lod -160 µs)
2021-02-11 -> 2031-12-31 (-) UT1-UTC +0.511 ± 0.125 s (lod -170 µs)
2021-02-18 -> 2030-12-31 (-) UT1-UTC +0.488 ± 0.116 s (lod -180 µs)
2021-02-25 -> 2030-12-31 (-) UT1-UTC +0.526 ± 0.116 s (lod -190 µs)
2021-03-04 -> 2030-06-30 (-) UT1-UTC +0.502 ± 0.111 s (lod -200 µs)
2021-03-11 -> 2029-12-31 (-) UT1-UTC +0.525 ± 0.107 s (lod -210 µs)
2021-03-18 -> 2029-12-31 (-) UT1-UTC +0.559 ± 0.107 s (lod -220 µs)
2021-03-25 -> 2028-12-31 (-) UT1-UTC +0.509 ± 0.097 s (lod -230 µs)
2021-04-01 -> 2028-12-31 (-) UT1-UTC +0.538 ± 0.097 s (lod -240 µs)
2021-04-08 -> 2028-12-31 (-) UT1-UTC +0.564 ± 0.097 s (lod -250 µs)
2021-04-15 -> 2028-12-31 (-) UT1-UTC +0.561 ± 0.097 s (lod -250 µs)
2021-04-22 -> 2028-06-30 (-) UT1-UTC +0.515 ± 0.092 s (lod -260 µs)
2021-04-29 -> 2028-06-30 (-) UT1-UTC +0.514 ± 0.092 s (lod -260 µs)
2021-05-06 -> 2028-06-30 (-) UT1-UTC +0.512 ± 0.091 s (lod -260 µs)
2021-05-13 -> 2028-12-31 (-) UT1-UTC +0.578 ± 0.096 s (lod -260 µs)
2021-05-20 -> 2028-12-31 (-) UT1-UTC +0.573 ± 0.096 s (lod -260 µs)
2021-05-27 -> 2028-12-31 (-) UT1-UTC +0.569 ± 0.096 s (lod -260 µs)
2021-06-03 -> 2028-12-31 (-) UT1-UTC +0.539 ± 0.095 s (lod -250 µs)
2021-06-10 -> 2028-12-31 (-) UT1-UTC +0.536 ± 0.095 s (lod -250 µs)
2021-06-17 -> 2028-12-31 (-) UT1-UTC +0.534 ± 0.095 s (lod -250 µs)
2021-06-24 -> 2028-12-31 (-) UT1-UTC +0.534 ± 0.095 s (lod -250 µs)
2021-07-01 -> 2028-12-31 (-) UT1-UTC +0.534 ± 0.095 s (lod -250 µs)
2021-07-08 -> 2028-12-31 (-) UT1-UTC +0.531 ± 0.094 s (lod -250 µs)
2021-07-15 -> 2028-12-31 (-) UT1-UTC +0.527 ± 0.094 s (lod -250 µs)
2021-07-22 -> 2028-12-31 (-) UT1-UTC +0.522 ± 0.094 s (lod -250 µs)
2021-07-29 -> 2029-06-30 (-) UT1-UTC +0.509 ± 0.099 s (lod -240 µs)
2021-08-05 -> 2029-06-30 (-) UT1-UTC +0.505 ± 0.098 s (lod -240 µs)
2021-08-12 -> 2029-06-30 (-) UT1-UTC +0.505 ± 0.098 s (lod -240 µs)
2021-08-19 -> 2029-12-31 (-) UT1-UTC +0.546 ± 0.103 s (lod -230 µs)
2021-08-26 -> 2029-12-31 (-) UT1-UTC +0.548 ± 0.103 s (lod -230 µs)
2021-09-02 -> 2029-12-31 (-) UT1-UTC +0.550 ± 0.102 s (lod -230 µs)
2021-09-09 -> 2029-12-31 (-) UT1-UTC +0.551 ± 0.102 s (lod -230 µs)
2021-09-16 -> 2029-12-31 (-) UT1-UTC +0.554 ± 0.102 s (lod -230 µs)
2021-09-23 -> 2029-12-31 (-) UT1-UTC +0.556 ± 0.102 s (lod -230 µs)
2021-09-30 -> 2029-12-31 (-) UT1-UTC +0.558 ± 0.102 s (lod -230 µs)
2021-10-07 -> 2029-12-31 (-) UT1-UTC +0.560 ± 0.102 s (lod -230 µs)
2021-10-14 -> 2029-12-31 (-) UT1-UTC +0.532 ± 0.101 s (lod -220 µs)
2021-10-21 -> 2029-12-31 (-) UT1-UTC +0.533 ± 0.101 s (lod -220 µs)

Tony.
-- 
f.anthony.n.finch  <dot@dotat.at>  https://dotat.at/
Lundy, Fastnet, Irish Sea: Southwest 6 or 7, increasing gale 8 at
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