[PROPOSED] Sub-second history for Maputo and Zurich
* africa (Africa/Maputo), europe (Europe/Zurich): Add #STDOFF comments for two zones with well-sourced standard time that was not an integral number of seconds away from UT. This does not change the TZif output files. --- africa | 5 +++-- europe | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/africa b/africa index 695d66ed..4f0d1e7b 100644 --- a/africa +++ b/africa @@ -1101,11 +1101,11 @@ Zone Africa/El_Aaiun -0:52:48 - LMT 1934 Jan # El Aaiún # Zambia # Zimbabwe # -# From Paul Eggert (2024-04-09): +# From Paul Eggert (2024-05-24): # The London Gazette, 1903-04-03, page 2245, says that # as of 1903-03-03 a time ball at the port of Lourenço Marques # (as Maputo was then called) was dropped daily at 13:00:00 LMT, -# corresponding to 22:49:41.7 GMT; round this to UT+2:10:18. +# corresponding to 22:49:41.7 GMT, so local time was +02:10:18.3. # Conversely, the newspaper South Africa, 1909-02-09, page 321, # says the port had just installed an apparatus that communicated # "from the controlling clock in the new Observatory at Reuben Point ... @@ -1116,6 +1116,7 @@ Zone Africa/El_Aaiun -0:52:48 - LMT 1934 Jan # El Aaiún # For lack of better info, list 1909 as the transition date. # # Zone NAME STDOFF RULES FORMAT [UNTIL] + #STDOFF 2:10:18.3 Zone Africa/Maputo 2:10:18 - LMT 1909 2:00 - CAT diff --git a/europe b/europe index 9ea14914..2f180e64 100644 --- a/europe +++ b/europe @@ -3486,8 +3486,8 @@ Zone Atlantic/Canary -1:01:36 - LMT 1922 Mar # Las Palmas de Gran C. # but if no one is present after 11 at night, could be postponed until one # hour before the beginning of service. -# From Paul Eggert (2013-09-11): -# Round BMT to the nearest even second, 0:29:46. +# From Paul Eggert (2024-05-24): +# Express BMT as 0:29:45.500, approximately the same precision 7° 26' 22.50". # # We can find no reliable source for Shanks's assertion that all of Switzerland # except Geneva switched to Bern Mean Time at 00:00 on 1848-09-12. This book: @@ -3526,6 +3526,7 @@ Rule Swiss 1941 1942 - May Mon>=1 1:00 1:00 S Rule Swiss 1941 1942 - Oct Mon>=1 2:00 0 - # Zone NAME STDOFF RULES FORMAT [UNTIL] Zone Europe/Zurich 0:34:08 - LMT 1853 Jul 16 # See above comment. + #STDOFF 0:29:45.500 0:29:46 - BMT 1894 Jun # Bern Mean Time 1:00 Swiss CE%sT 1981 1:00 EU CE%sT -- 2.43.0
On Fri 2024-05-24T15:33:23-0700 Paul Eggert via tz hath writ:
* africa (Africa/Maputo), europe (Europe/Zurich): Add #STDOFF comments for two zones with well-sourced standard time that was not an integral number of seconds away from UT. This does not change the TZif output files.
I urge great caution for the use of subsecond offsets. In 1853 some observatories were still calculating their time using tables of the motion of earth which were based on recent observations of the sun, whereas other observatories had begun to use tables of the motion of earth based on perturbation theory where the mean sun was calculated over an interval of millennia where the resonance 3*Jupiter - 8*Mars + 4*Earth (with a period of about 1850 years) moved the mean mean sun 0.5 time second away from tables based on recent observations of the sun. As late as the 1920s the tabulations of received time signals in BIH Bulletin Horaire show that different radio broadcasts of Universal Time differed from each other by 0.2 time second or more. Even as late as 1958 the USNO radio broadcasts differed from the BIH value of UT2 by 0.03 time second because the values USNO used for its longitudes and the values BIH used for longitudes were not expressed in a globally consistent reference frame. -- 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
On 2024-05-24 16:29, Steve Allen via tz wrote:
I urge great caution for the use of subsecond offsets.
Yes, and even offsets with one-second precision are dicey for older civil time; see, for example, the comments in 'europe' about Dunsink Mean Time. The subsecond offsets are put in mostly just to document the legal or announced definition of local time. Come to think of it, it's not entirely clear that Bern Mean Time legally corresponded to 7° 26' 22.50". The source for that meridian is here: https://www.admin.ch/opc/de/classified-compilation/20071096/index.html but this comes from government publications dated May 2008. It'd be better to cite a source for BMT during the period 1853 to 1894 when it was actually being observed. From the point of view of TZif files the subsecond offsets are all trivia, since the subsecond info doesn't affect them.
participants (2)
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Paul Eggert -
Steve Allen