LMT information, geographics of Antarctica bases
Oscar van Vlijmen
ovv at hetnet.nl
Tue Mar 22 16:18:22 UTC 2005
>> Some LMT (local mean time) values in the tz database seem to be incorrect.
>> Below are the values I believe to be correct.
> These LMT offsets agree with the current tz database.
>> Alaska America/Yakutat -9:14:55
> Are you sure about that one?
I found out what the problem was.
The tz northamerica file says:
Zone America/Yakutat 14:41:05 - LMT 1867 Oct 18
-9:18:55 - LMT 1900 Aug 20 12:00
I took the _first_ LMT for granted and reported this could be an error.
But let's look at the file zone.tab:
US +593249-1394338 America/Yakutat Alaska Time - Alaska panhandle
The longitude -139:43:38 translated to LMT becomes: -09h 18m 54.53s
BTW, I made a typo: 14m instead of the correct 18m.
It is not always true that the _last_ LMT entry is correct in the sense of
true solar LMT.
Take for instance, from the africa file:
Zone Africa/Sao_Tome 0:26:56 - LMT 1884
-0:36:32 - LMT 1912 # Lisbon Mean Time
The first LMT time is the true solar LMT time.
First or second LMT entry: it is not always an international date line
effect. Take for instance (tz southamerica file):
Zone America/Lima -5:08:12 - LMT 1890
-5:08:36 - LMT 1908 Jul 28 # Lima Mean Time?
The first LMT is the time, calculated from the longitude given in zone.tab.
Just by inspecting the Zone information in the tz database files it is not
always clear what the true solar LMT is.
The true LMT has to be calculated from the zone.tab location information.
It could be advised to document this somewhere, or to remove the ambiguities
in the LMT data.
The following zones have two LMT entries, as far as I detected, and I
recalculated the true solar LMT from the zone.tab data, the 180 degree
meridian being the natural border between + and -:
Zone Africa/Sao_Tome LMT = 00:26:56
Zone Asia/Manila LMT = 08:04:00
Zone Pacific/Guam LMT = 09:39:00
Zone Pacific/Saipan LMT = 09:43:00
Zone Pacific/Pago_Pago LMT = -11:22:48
Zone Pacific/Apia LMT = -11:26:56
Zone Europe/Lisbon LMT = -00:36:32
Zone America/Juneau LMT = -08:57:41
Zone America/Yakutat LMT = -09:18:55
Zone America/Anchorage LMT = -09:59:36
Zone America/Adak LMT = -11:46:38
Zone America/Lima LMT = -05:08:12
Oscar van Vlijmen
More information about the tz