Re: [boost] Re: reminder about Date/Time formal review

From: William E. Kempf (williamkempf_at_[hidden])
Date: 2002-04-26 08:33:33

----- Original Message -----
From: "Victor A. Wagner, Jr." <vawjr_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Friday, April 26, 2002 1:13 AM
Subject: Re: [boost] Re: reminder about Date/Time formal review

> Adding to the pedantry, my reference "Supplement to the American Ephemeris
> and Nautical Almanac" Britain and what is now the U.S.  (it wasn't the
U.S.
> in 1751) adopted the Gregorian calendar on the same day, so July 4, 1751
> was the same day both in England _and_ the colonies.... by implication,
> July 4th 1752 was ALSO the same day.

OK, this I did not know.  I'm not aware of when the various regions adopted
the Gregorian system.

> At Wednesday 2002/04/24 07:37, you wrote:
> >[deleted]
> >Gotta
> > > > > love this date stuff, no?)
> > > >
> > >
> > > Wrong. Gregorian dates are not dependant on where your are in this
way.
> >What
> > > is dependant is which colander was in use.
> >
> >July 4, 1751 in the US was a very different day then July 4, 1751 in
> >England.  The reason, as you point out (and I thought was obvious from
what
> >I posted) is because the US didn't adopt the Gregorian system until Sept.
> >14, 1752... or, more precisely, they adopted it on Sept. 2, 1752, which
> >immediately became Sept. 14, 1752.  The point is, you can't project dates
> >backwards with out knowing the location as well as the date.  Further,
the
> >"change over" date also effects this.  If the change over date used by
the
> >system were the American Sept. 14, 1752 this would mean the algorithm
> >doesn't take into account things such as the missing day added at this
time
> >when dates are projected further back.
> >
> > > Gregorian (Sept 14, 1752)-1 = Gregorian(Sept 13, 1752) = Julian(Sept
2,
> > > 1752)
> >
> >The above isn't accurate.  Gregorian (Sept. 14, 1752) - 1 = Gregorian
(Sept.
> >12, 1752)
>
> Ummm, I think you mean Gregorian(Sept. 13, 1752) .... not 12

No, I meant 12.

> >if you were in one of the regions that adopted the Gregorian
> >calendar in 1582, or Julian (Sept. 2, 1742) if you were in America or one
of
> >the other locations that was still using the Julian calendar.  The
problem
> >is that the Gregorian calendar has not been a stable system, with 10 days
> >being added to the Julian system in 1582 and 11 days being added in 1752
> >when America switched over.
>
> There weren't 11 days "added" to the Gregorian calendar in 1752, the
> Gregorian calendar and the Julian calendar were the 11 days apart (as
> opposed to 10 days apart in Oct 1582 when pope Gregory decreed the
original
> change).  I have no idea what you mean by "not been a stable system"

This contradicts the sources I have, but I'm not a domain expert.

Bill Kempf