Hello, The current integer leap second system did not exist before 1972. There were a number of fractional-second adjustments and there were also frequency adjustments starting in the 1950s, when the length of the cesium second was defined. The final time adjustment at the start of 1972 was intended to incorporate the integral of the previous frequency steps, since the frequency of UTC was set equal to the SI second at that time. It is quite challenging to compute time intervals in the pre-1972 era. Different timing laboratories had slightly different values for this final time step. The goal was to bring all of the real-time realizations of UTC to the same time. Judah Levine On: 09 November 2018 22:29, "Steve Allen" <sla@ucolick.org<mailto:sla@ucolick.org>> wrote: On Fri 2018-11-09T22:04:35-0700 Paul Gilmartin via tz hath writ:
Subject: [tz] Was there a 1971-12-31 23:59:60?
No. There was a step of 0.107758 seconds in UTC(BIH) at 1972-01-01. This was the final sub-second step in coordinated broadcast time signals. for the step that was applied to UTC(USNO) see Time Service Announcement series 14 number 8 (1971-10-08) at https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fwww.ucolick.org%2F~sla%2Fleapsecs%2Fleapincept.html&data=02%7C01%7CJudah.Levine%40nist.gov%7Cbe5617bc38fd469863b508d646cd8a53%7C2ab5d82fd8fa4797a93e054655c61dec%7C1%7C0%7C636774245940004523&sdata=Ju3hU%2FPYznG15Udu9qFK4yfC9%2FJDJDfRXN6igfWXq5k%3D&reserved=0 -- Steve Allen <sla@ucolick.org<mailto: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 &nb
On Sat 2018-11-10T19:54:11+0000 Levine, Judah Dr. (Fed) hath writ:
It is quite challenging to compute time intervals in the pre-1972 era.
That depends on the required precision. It is still challenging to compute intervals to nanoseconds. That requires grabbing all the relevant issues of BIPM Circular T and similar publications of the particular source of time if they are not members of the BIPM atomic clock club. One hundred years ago it was challenging to compute intervals to centiseconds, and that was the reason for the creation of BIH. When Anna Stoyko retired from the BIH in 1965 she published one final analysis of all the BIH data from 1922 to 1963. She produced plots showing how the time services of observatories had improved. Those plots are reproduced here https://www.ucolick.org/~sla/leapsecs/annastoyko.html In order to gather these data the BIH had been monitoring the arrival times of radio broadcast time signals since 1922. The volumes of Bulletin Horaire have the numbers that show many ways that various national observatories and time services messed up (and messed around with) the time they were providing. The data in the issues of Bulletin Horaire are the nightmare of the tzdb because taken to the absurd limit they would require that tzdb encode the millisecond-scale differences between the legal civil times of every nation whose transmitters were monitored by BIH.
Different timing laboratories had slightly different values for this final time step. The goal was to bring all of the real-time realizations of UTC to the same time.
Well, much closer than before, but if they were the same then the subsequent issues of BIH Bulletin Horaire and now BIPM Circular T would be much terser publications. -- 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 http://www.ucolick.org/~sla/ Hgt +250 m
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