[tz] switches at 1883-11-18 at the same instant
eggert at cs.ucla.edu
Mon Mar 19 22:51:00 UTC 2018
On 03/19/2018 03:09 PM, Michael H Deckers via tz wrote:
> the switch was done at a single instant, when UT was 1883-11-18 + 18 h.
> This differs from the current description in tzdb which uses
> different instants
> for different target time zones -- not a likely choice for
> simplifying a nationwide
> railway schedule.
But we have a reliable eyewitness account that New York had two noons
that day. See the quotation from William F. Allen in the "northamerica"
file, taken from Bartky's 1989 paper
<http://dx.doi.org/10.2307/3105430>. So the New York switch cannot have
been at 18:00 GMT that day, as that would have meant two instances of
13:00, not two instances of 12:00. Bartky writes that it was called the
"day of two noons" because eastern parts of the new zones observed noon
twice, which wouldn't have happened if everyone switched at 18:00 GMT.
Allen also wrote that New York got its time signal from the Naval
Observatory, not from the Allegheny Observatory. Back then, different
observatories were competing for the time-setting business. Perhaps the
SpaceWatchtower sources included Allegheny partisans? (It's hard to tell
from its source list.)
It's possible that parts of the US switched at around 12:00 local time
while other parts switched at 18:00 GMT; but if that's the case, I'd
like sources for which parts switched which way.
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