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2176Re: UTC didn't exist before 1961

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  • johnmsteele
    May 23, 2009
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      In a very strict technical sense it may have been overlooked.

      However, prior to atomic clocks, you have to relax the formality of beating in synch with atomic clocks. It obviously approximates (within 0.9 s, that is why leap seconds are used) mean solar time at Greenwich. Formerly that time was kept as GMT or UT1 (Note: GMT had a confusing period where astronomers counted from noon, and civilly, hours were counted from midnight). GMT was used from 1884 when Greenwich was accepted by international convention as the Prime Meredian (and used by many nations prior to that).

      Your bigger problem is when did political entities switch from local mean solar time to standard time. In most places it was adopted first by railroads and some local entitites, eventually national. The US was 1918, with some prior use by individual cities and states.

      The "Z" designation for time at Greenwich was used long before UTC.

      I think your 1961 boundary can be pushed back to when the country of interest declared "standard time" (if you can determine how many hours off Greenwich. There are a LOT of time zone changes.)

      Prior to standard time, there may be a problem, although if you know the longitude of a place, you could calculate the time shift from Greenwich to the nearest minute (1 hour/15°). Rarely are times back then known with any great accuracy.

      --- In ISO8601@yahoogroups.com, "pqrc96" <pqrc96@...> wrote:
      > Some people who write in Wikipedia are interested in using
      > microformats to provide a machine-readable version of important dates
      > and times, in the hopes that future software will be better able to
      > mine data from articles. Dates and times in microformat purport to
      > conform to the ISO 8601 standard, but at least in the case of
      > Wikipedia, the people interested in implementing this sort of thing
      > don't have a clear understanding of time zones or the need to use
      > the Gregorian calendar. Upon re-reading the standard to see if some
      > of these items could be cleared up, I noticed that the standard has
      > an oversignt, in that it allows for dates and times before the
      > beginning of UTC but does not provide a way to specify a time zone
      > for these dates, because doing so requires UTC. In a standard that
      > is so careful to explain the meaning of every single character, this
      > seems like an error. Of course, people will go ahead and extend it
      > backward however they please, but strictly speaking, they are no
      > longer using ISO 8601, they are using their own private extension.
      > --- In ISO8601@yahoogroups.com, "johnmsteele" <johnmsteele@> wrote:
      > > . . .
      > > What are you trying to do exactly and what time records are you
      > having
      > > trouble relating to UTC?
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