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

From: Andrew J. P. Maclean (a.maclean_at_[hidden])
Date: 2002-04-28 18:15:20

In the code I sent you there is a routine that calculates the Gregorian
Julian Date difference. This was specifically written to allow users to
specify the date of the changeover from Julian to Gregorian, because, as
you have discovered, this occurred at different times in different
countries. I believe that the latest date for changeover was around
1925, which, I think puts the difference between the Julian and
Gregorian calendar at around 12 days.

Andrew

___________________________________________
Andrew J. P. Maclean
Postal:
Australian Centre for Field Robotics
The Rose Street Building J04
The University of Sydney  2006  NSW
AUSTRALIA
Room:
106
Phone:
[phone]
Fax:
[phone]

http://www.acfr.usyd.edu.au/
___________________________________________

-----Original Message-----
From: boost-admin_at_[hidden] [mailto:boost-admin_at_[hidden]]
On Behalf Of William E. Kempf
Sent: Friday, 26 April 2002 23:34
To: boost_at_[hidden]
Subject: Re: [boost] Re: reminder about Date/Time formal review

----- 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