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DATETIME  November 2015

DATETIME November 2015

Subject:

Re: 1/27 conference call notes: an instant can't be on 3 different days

From:

"Byrd, Donald A." <[log in to unmask]>

Reply-To:

Discussion of the Developing Date/Time Standards <[log in to unmask]>

Date:

Mon, 23 Nov 2015 20:35:54 +0000

Content-Type:

text/plain

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Parts/Attachments

text/plain (33 lines)

There's only one International Date Line; time zones on the earth span just 24 hours. So it seems to me an instant can't be on more than two different days, regardless of where and when it occurs. Munich's time zone is nine (I think) hours west of the Date Line, so an event at, say, 11:45 PM on Nov. 30 there is on December 1 anywhere more than a few hundred kilometers (or some such) to its east, up to the date line. It's 15 hours from the Date Line in the other direction, so the earliest it can be in any time zone is 15 hours earlier, i.e., 8:45 AM on Nov. 30.

Furthermore, an instant also can't be on _less_ than two different days,  regardless of where and when it occurs. Well, it could be argued that an instant at exactly midnight somewhere is an exception! Anyway, for practical purposes, every instantaneous event occurs on exactly two different days.

Am I thinking clearly?

--Don


On Nov 19, 2015, at 5:13 PM, "Denenberg, Ray" <[log in to unmask]> wrote:

> So Neil Armstrong’s moon event is nominally 1969-07-20, that’s the “official” date that it occurred (nevermind that it was on the moon, let’s just say July 20 is the “real” date, for discussion sake). Some observers may have recorded it as July 19.   And I suppose somewhere else it was recorded as July 21.  Would you call this “two-day” precision?  Three-day precision?
> 
> An event in Munich may occur close to midnight so it is the next day in Samoa (and the previous day somewhere else?)  But it might be November 30 in Munich, so it is December in Samoa, or it might be December 31 in Munich so it is the next year in Samoa.  So the first case is 2 (or 3) day precision, the second is month precision and the third year precision.  And maybe it occurred 2009, so there you have decade precision.
> 
> Still, all these examples are based on cases where the estimate is no more than a day off.  I don’t think I can convince the ISO people based on that. Are there other examples?
> 
> Ray
> 
>> -----Original Message-----
>> From: Discussion of the Developing Date/Time Standards
>> 
>> [---- SNIP ----]



---
Donald Byrd
Woodrow Wilson Indiana Teaching Fellow
Adjunct Associate Professor of Informatics
Visiting Scientist, Research Technologies
Indiana University Bloomington

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