[LEAPSECS] Historican timezones (Was: Re: Looking-glass, through)

Warner Losh imp at bsdimp.com
Wed Jan 12 18:59:36 EST 2011

On 01/12/2011 15:41, Paul Sheer wrote:

> The Olson time library has all historican timezone information.


> You can choose a zone, a time (back to the 1800's) and deduce

> the precise zone offset in minutes and seconds.


> This is inclusive of wierd time zones that were based on the hour

> since sunrise (or some similar wierd thing), as well as more basic

> things like daylight savings that were tried one year, and revoked

> the following year by that countries government.


> There are 3064 rules in the Olson time library zone files and 434

> time zones, as well as GPS information for each zone.


> It would seem a number of maintainers do track time zone

> announcements from all over the world and keep these

> rules up to date. The most recent update was November 2010.


> Further, people updating the zone rules usually provide references

> for the rule change, citing a government announcement.

The Olson database is good for things since the 80's or 90's. Prior to
that, the further that you go back in the past, the less reliable and
complete the information gets. Since then the information has been
updated in real time. Prior to that it was based on research for
different areas and some of that data is still extant, while other data
might not be.

Don't get me wrong, or take this as me saying that the maintainers of
this database haven't done a herculean job of making it the best we
have. The problem is that it is hard to know for sure all the details
you need to for historical times the further back into the past you get.

There's even a nice disclaimer:

# This data is by no means authoritative;....
# I invented the abbreviations marked '*' in the following table


Consulting these files show that I was wrong about the 1850's date for
time zones. They were invented in 1870 and adopted on 1883-11-18 at
12:00 by all the railroads and the rest of the country followed suit.


> -paul



> On Wed, 2011-01-12 at 20:48 +0000, Clive D.W. Feather wrote:

>> Rob Seaman said:

>>> For instance, what authority will historians or lawyers consult to learn the applicable timezone offsets that were in force in some location(s) during some epoch(s) in question?

>> <FX: falls about laughing>


>> Those of us on the timezone list can't even find out this information for

>> this year for many places. It's almost impossible to determine it for (say)

>> 200 years ago for almost anywhere.


>> This is *nothing* to do with what the underlying time scale is. Tony has it

>> right: you have things completely backwards.


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