From: Nicholas Strauss <nicholas.strauss@gmail.com>
To: Glenn Morris <rgm@gnu.org>
Cc: 20583@debbugs.gnu.org, gjs@ai.mit.edu
Subject: bug#20583: calendar-absolute-from-gregorian
Date: Fri, 15 May 2015 18:48:02 -0700 [thread overview]
Message-ID: <CAAgRMMJqc+_Mr2_CJx9tUcj0Fn8HWXedLP+J4OnTVmypc=pH5w@mail.gmail.com> (raw)
In-Reply-To: <577fs9xryr.fsf@fencepost.gnu.org>
Hi Glenn,
The real point here is that Calendar Systems are instruments and as
subject are subject to error (Think like an engineer!). The real world
is messy -- Pope Gregory abolished some days, and various countries
took their time to jump on the band wagon.
I think what Reingold is/was trying to do was to use "absolute" as an
internal reference format -- a primary key -- that would correlate all the
other calendars.
there are other "absolute" choices for internal references.
Peter Duffett-Smith took a different approach -- he counts 2415020
days from January 1, 4713 BC until the 1900 epoch, January 0.5, 1900.
This crops up in sqlite3 calculations for date() and also common
javascript formulas.
I am still researching this.
If our civilization lasts for any appreciable time, having a consistent
calendar will be crucial for keeping a consistent history.
I think this helps why I am stressing the astronomy. If an Aztec calendar
records an eclipse on a certain day, that's pretty much it.
Nick
On Fri, May 15, 2015 at 5:54 PM, Glenn Morris <rgm@gnu.org> wrote:
> Nicholas Strauss wrote:
>
>> Why does (calendar-absolute-from-gregorian '(10 10 1582))
>> return 577731?
>> (calendar-generate '(10 1582)) is another example of this
>> error.
>
> It's behaving as designed. It's a utility function that operates on the
> basis that today's calendar system is valid for all time. It's not meant
> as literally historically accurate, and I think trying to make it so (by
> introducing discontinuities at certain dates) would be a mistake. See eg
> thread at:
>
> http://lists.gnu.org/archive/html/emacs-devel/2006-07/msg01008.html
next prev parent reply other threads:[~2015-05-16 1:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-15 4:20 bug#20583: calendar-absolute-from-gregorian Nicholas Strauss
2015-05-16 0:54 ` Glenn Morris
2015-05-16 1:48 ` Nicholas Strauss [this message]
2015-05-22 15:36 ` Nicholas Strauss
2015-05-24 15:29 ` Nicholas Strauss
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