On Wed 2017-11-08T01:08:34+0800 Philip Paeps hath writ:
I wonder if it wouldn't be easier to simply note "where we write UTC, we actually mean UT when referring to timestamps before UTC was introduced".
This makes it tricky to include contemporary documents which originally used one or the other. In many of those cases the usage was uninformed and often the term used was inappropriate for the actual meaning. The inception of all the forms of UT (UT0, UT1, UT2), and their usage, is available in issues of BIH's Bulletin Horaire from 1955. See https://www.ucolick.org/~sla/leapsecs/BH1955.html So definitions for terms related to UT are easy to pinpoint. It is much harder pinpoint UTC. The inception of UTC in print is found in Bulletin Horaire, Series J, No. 1 (1964 Jan/Feb) which was not actually prepared for printing until after 1965-05-01. That first use in print does not declaratively define UTC, but rather employs a term which had evidently been in informal use since some point after 1961 January. Nevertheless, most publications and radio broadcasts continued to use the term GMT or UT (and often local legal civil time) into the 1970s even when they were broadcasting signals that would better have been called UTC. The first documented use of the term UTC in radio broadcast time signals is by WWV and WWVH starting 1974-01-01. There is no formal definition of the term UTC until the 13th Plenary Assembly of the CCIR approved Recommendation 460-1 during 1974 July. Nevertheless, the distinction between UT,UT0,UT1,UT2 and UTC is clear from the proceedings during the decades from the 1950s through the 1970s. UT is a time scale derived directly from observation of the rotation of the earth in a way that subdivides days of the calendar. UTC was always a time scale derived from atomic chronometers and adjusted to remain within specified close agreement to UT. -- 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