On 2020-02-04 13:44, Tony Finch wrote:
The IERS Bulletins C state a value of UTC-TAI "until further notice". However the machine-readable files from IERS and NIST give an expiry date of a few days less than 6 months after the announced (lack of) leap second, or a bit more than 11 months after the latest Bulletin C. Is this expiry date reliable or just advisory? History suggests it's reliable, but the standards do not. It's unclear to me what governs the frequency of announcements or their validity period, i.e. where are current practices documented? what is the process for changing them? how will we know if a change is planned? and so on. This is all about how much we can assume that the IERS will continue to operate leap seconds as they have for nearly 50 years, or whether they will make use of the much weaker guarantees given by TF.460, or (wishful thinking) whether they can schedule leap seconds further in the future.
The IERS (and BIH) policy to use only the primary choices for the insertions of leap seconds is only guaranteed in the text of Bulletin C -- if LOD increases sufficiently, that text will have to change. There is a similar situation for Bulletins D -- each of them announces when the next one is expected to be issued. But even nowadays these predictions of UT1 - UTC are not very reliable, and they often err on the "wrong" side (DUT1 changes earlier than predicted). For instance, Bulletins D139, D134, and D129 each came earlier than predicted by the preceding Bulletin D; Bulletin D129 (of 2016-04-15) was even significantly earlier (45 d) than predicted by Bulletin D128 (of 2016-02-19). Michael Deckers. _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
