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[Emacs-diffs] Changes to emacs/doc/misc/calc.texi,v
From: |
Glenn Morris |
Subject: |
[Emacs-diffs] Changes to emacs/doc/misc/calc.texi,v |
Date: |
Thu, 06 Sep 2007 05:10:25 +0000 |
CVSROOT: /sources/emacs
Module name: emacs
Changes by: Glenn Morris <gm> 07/09/06 05:10:13
Index: calc.texi
===================================================================
RCS file: /sources/emacs/emacs/doc/misc/calc.texi,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -b -r1.1 -r1.2
--- calc.texi 6 Sep 2007 04:58:46 -0000 1.1
+++ calc.texi 6 Sep 2007 05:10:12 -0000 1.2
@@ -1,7 +1,7 @@
\input texinfo @c -*-texinfo-*-
@comment %**start of header (This is for running Texinfo on a region.)
@c smallbook
address@hidden ../info/calc
address@hidden ../../info/calc
@c [title]
@settitle GNU Emacs Calc 2.1 Manual
@setchapternewpage odd
@@ -11053,44 +11053,17 @@
days 0 and @mathit{-1} respectively in Calc's internal numbering scheme.
@cindex Julian day counting
-Another day counting system in common use is, confusingly, also called
-``Julian.'' The Julian day number is the numbers of days since
-12:00 noon (GMT) on Jan 1, 4713 BC, which in Calc's scheme (in GMT)
+Another day counting system in common use is, confusingly, also
+called ``Julian.'' It was invented in 1583 by Joseph Justus
+Scaliger, who named it in honor of his father Julius Caesar
+Scaliger. For obscure reasons he chose to start his day
+numbering on Jan 1, 4713 BC at noon, which in Calc's scheme
is @mathit{-1721423.5} (recall that Calc starts at midnight instead
-of noon). Thus to convert a Calc date code obtained by unpacking a
-date form into a Julian day number, simply add 1721423.5 after
-compensating for the time zone difference. The built-in @kbd{t J}
-command performs this conversion for you.
-
-The Julian day number is based on the Julian cycle, which was invented
-in 1583 by Joseph Justus Scaliger. Scaliger named it the Julian cycle
-since it is involves the Julian calendar, but some have suggested that
-Scaliger named it in honor of his father, Julius Caesar Scaliger. The
-Julian cycle is based it on three other cycles: the indiction cycle,
-the Metonic cycle, and the solar cycle. The indiction cycle is a 15
-year cycle originally used by the Romans for tax purposes but later
-used to date medieval documents. The Metonic cycle is a 19 year
-cycle; 19 years is close to being a common multiple of a solar year
-and a lunar month, and so every 19 years the phases of the moon will
-occur on the same days of the year. The solar cycle is a 28 year
-cycle; the Julian calendar repeats itself every 28 years. The
-smallest time period which contains multiples of all three cycles is
-the least common multiple of 15 years, 19 years and 28 years, which
-(since they're pairwise relatively prime) is
address@hidden @math{15\times 19\times 28 = 7980} years.
address@hidden 15*19*28 = 7980 years.
-This is the length of a Julian cycle. Working backwards, the previous
-year in which all three cycles began was 4713 BC, and so Scalinger
-chose that year as the beginning of a Julian cycle. Since at the time
-there were no historical records from before 4713 BC, using this year
-as a starting point had the advantage of avoiding negative year
-numbers. In 1849, the astronomer John Herschel (son of William
-Herschel) suggested using the number of days since the beginning of
-the Julian cycle as an astronomical dating system; this idea was taken
-up by other astronomers. (At the time, noon was the start of the
-astronomical day. Herschel originally suggested counting the days
-since Jan 1, 4713 BC at noon Alexandria time; this was later amended to
-noon GMT.) Julian day numbering is largely used in astronomy.
+of noon). Thus to convert a Calc date code obtained by
+unpacking a date form into a Julian day number, simply add
+1721423.5. The Julian code for @samp{6:00am Jan 9, 1991}
+is 2448265.75. The built-in @kbd{t J} command performs
+this conversion for you.
@cindex Unix time format
The Unix operating system measures time as an integer number of
@@ -16683,9 +16656,9 @@
@cindex Julian day counts, conversions
The @kbd{t J} (@code{calc-julian}) address@hidden command converts
a date form into a Julian day count, which is the number of days
-since noon (GMT) on Jan 1, 4713 BC. A pure date is converted to an
-integer Julian count representing noon of that day. A date/time form
-is converted to an exact floating-point Julian count, adjusted to
+since noon on Jan 1, 4713 BC. A pure date is converted to an integer
+Julian count representing noon of that day. A date/time form is
+converted to an exact floating-point Julian count, adjusted to
interpret the date form in the current time zone but the Julian
day count in Greenwich Mean Time. A numeric prefix argument allows
you to specify the time zone; @pxref{Time Zones}. Use a prefix of
- [Emacs-diffs] Changes to emacs/doc/misc/calc.texi,v,
Glenn Morris <=