On Fri 2020-11-13T22:38:56-0500 Kevin Kenny hath writ:
Most applications that are neither astronomical nor navigational find it convenient to treat the nominal time since epoch as "86400 times the number of days since 1 January 1970 + the number of elapsed seconds in the current day." The reason for ignoring leap seconds is that a great many applications deal with *civil* dates and times in the future, and it is impossible to predict more than a year or two in advance when a leap second might occur.
Not "Most". All. Even in astronomy and navigation. Every technical person involved in the process knew this in 1970 when the decision was made to implement leap seconds. Every technical system continued to use an underlying continous count of seconds, SI seconds of TAI for radio broadcasts and automated navigation systems, and mean solar seconds of UT for almanacs of astronomical phenomena. If the underlying count of seconds in POSIX were based on TAI then leap seconds do not cause more trouble for planning future civil events than is already caused by bureaucrats changing time zones. Technically it was only feasible to run radio broadcast, collision avoidance, or any laboratory systems using SI seconds. Legally it was necessary for calendar days to remain based on watching the sun in the sky. Each delegate to the international science and regulatory meetings could not introduce nor support a recommendation which would have been illegal in their country. The proceedings of the 1970 IAU referenced earlier include Gerhard Becker remarking that action was needed in order to make atomic-based time legal in all countries. He had already been saying, and would continue to say, the same at other meetings for several years, but he never got any traction. I suspect that is because the urgent need to create leap seconds was caused by the legislation Becker introduced in Germany which made old UTC illegal. I think nobody else wanted to risk pointing out to other governments how atomic time differed from watching the sun in the sky lest some other government make atomic time explicitly illegal and thus poison the possibility for all radio time broadcasts to agree worldwide. Agreement of all radio broadcast time signals was the reason that the 1912 time conference was called, the reason that BIH had come into existence, and a primary goal of the international time committees ever since then. Of all the persons visible in that 1970 IAU meeting, and at all the other meetings of other agencies, only H.M. Smith expressed happiness about UTC with leap seconds, and that was in the context of having found something on which all governments could agree. Every other memoir by folks who were part of the process contains tones of regret. Regret about the situation that we find ourselves in because POSIX chose a simple solution based on what was legal and available. But also the only feasible option because, unfortunately, after the sourness of the 1970 decision all of the technical principals backed away from the issue. Nobody created a means of distributing the history of leap second information more robust than having the BIH send letters to the heads of national time service bureaus. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m