From sla at ucolick.org Sun Dec 2 00:12:08 2018 From: sla at ucolick.org (Steve Allen) Date: Sat, 1 Dec 2018 21:12:08 -0800 Subject: [LEAPSECS] early efforts at uniform frequency Message-ID: <20181202051208.GA25814@ucolick.org> By the time of the 1950 meeting on Astronomical Constants held at Observatoire de Paris under the auspices of the CNRS the quartz clock engineers at Greenwich had some ocillators which were more stable than earth rotation. They still had a tendency for some of them to go rogue and stop being more stable, but with a large enough ensemble those could be identified and excluded. Using those quartz clocks made it possible to get a good measure of the seasonal variation of earth rotation. The BIH published the first expression for Delta T_S (what would become known as UT2-UT1) at the end of 1951. From 1952 through 1955 the UK radio broadcasts controlled by Greenwich were already applying that correction (as well as the UT1 correction they had started applying around 1947) to give a quasi-uniform time that they called Provisional Uniform Time (PUT). Before 1955 the USNO was also using such corrections in its radio broadcasts, and in 1955 their time scale was named N3c. The BIH published several subsequent expressions for the seasonal variation both before and after the IAU directed that all radio broadcasts should do that. The final version of UT2-UT1 was first used during 1962, by which point the time signal broadcasts were already regulated by cesium. Plots of the seasonal variation expressions are here https://www.ucolick.org/~sla/leapsecs/seasonal.html -- Steve Allen 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 From tvb at LeapSecond.com Mon Dec 31 16:16:53 2018 From: tvb at LeapSecond.com (Tom Van Baak) Date: Mon, 31 Dec 2018 13:16:53 -0800 Subject: [LEAPSECS] leap seconds rarely happen at midnight Message-ID: <20FF1A84286C4D20B8245D5E953EB29A@pc52> Nice take on time zones (applies to leap seconds also): https://xkcd.com/2092/ /tvb