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Unix System Administration Handbook 1997 October
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INDEX ENTRY FOR JULIAN:
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Name: Julian - Computes Julian dates
Version: N/A
Author(s): Ian Miller <Ian_Miller@bifroest.demon.co.uk> (current maintainer)
Henry F. Fliegel
Georgetown University Observatory
Washington DC
Thomas C. Van Flandern
U.S. Naval Observatory
Washington DC
On the CD-ROM in: sysadm/julian.tar
Ftp source: N/A
Size on the CD: 20 KB (uncompressed)
Description:
The simplest technique is probably to convert to a Julian Day
number and then take the result mod7. This has the advantage that
you can do a lot of other things with Julian Day number as well.
The best algorithm I know of was published as a letter from Henry
F Fliegel and Thomas C van Flandern in the October 1968 (vol 11
#10) issue of the Communications of the ACM.
Julian Day Number = day - 32075 + 1461 * (year + 4800 - (14 - month)/12)/4 +
367 * (month - 2 + (14 - month)/12*12)/12 -
3 * ((year + 4900 - (14 - month)/12)/100)/4
This is valid for all dates in the Gregorian Calendar up to 28 Feb
4000. (I have modified this algorithm slightly from the original
to avoid dividing negative numbers. The original only worked in
FORTRAN. The modified version should work in any language.)
-- Quoted from the README by Ian Miller
Advertised architectures: N/A
Prerequisites: C compiler or PERL