On Sun 2015-01-25T16:57:58 -0500, G Ashton hath writ: > Brooks Harris mentioned, at approximately Sun 1/25/2015 21:02 UT, a > "Gregorian timescale". I believe that since in Gregory's time there was no > alternative to making the passage of calendar days agree with the day/night > cycle, we must understand "Gregorian timescale" to mean either apparent or > mean solar time (unless an ecumenical council is called and declares > otherwise). Also, I am not at all sure that the Gregorian calendar has > always been used together with the convention that the new day begins at > midnight; I would like to be pointed to a reference that says that, if it > exists.
Most references are those of the common practice within some context. A few have the status of international recommendation. The tabulations of the UK Nautical Almanac were done in apparent solar time through 1832. Then the Admiralty decided that chronometers were ubiquitous enough that their use justified changing the tabulations to be done in mean solar time starting with 1833. The 1884 International Meridian Conference decided that the Universal Day was mean solar time, and they recommended that it should start at midnight. The UK and US almanacs started the day at noon through 1924. Starting in 1925 the almanacs switched to the civil practice of starting the day at midnight. The citable references for these transitions are linked within http://www.ucolick.org/~sla/leapsecs/timescales.html -- Steve Allen <s...@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 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 _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs