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From: steve@mahendo.Jpl.Nasa.Gov (3171)
Newsgroups: comp.misc
Subject: Re: Julian Date (was Re: Sorting by date)
Message-ID: <116@mahendo.Jpl.Nasa.Gov>
Date: Mon, 9-Nov-87 13:50:53 EST
Article-I.D.: mahendo.116
Posted: Mon Nov  9 13:50:53 1987
Date-Received: Wed, 11-Nov-87 06:46:41 EST
References: <513@mtxinu.UUCP> <763@cfa.cfa.harvard.EDU> <3060@psuvax1.psu.edu>
Organization: Jet Propulsion Labs, Pasadena, CA
Lines: 25
Summary: reference epoch for Julian day number

In article <3060@psuvax1.psu.edu>, flee@gondor.psu.edu (Felix Lee) writes:
> In article <763@cfa.cfa.harvard.EDU> wyatt@cfa.harvard.EDU (Bill Wyatt) writes:
> >in article <513@mtxinu.UUCP>, tim@mtxinu.UUCP (Tim Wood) says:
> >The standard internaltional meaning of Julian Day Number is the number
> >of days since GMT noon on Jan 1, 4713 B.C.
> What is the significance of 4713 BC?  The Julian calendar was instituted
> 46 BC.  4713 BC sounds like the creation of the world as calculated from
> the Bible.  But what does that have to do with Julius?

The following information is taken from the Explanatory Supplement to the
Astronomical Ephemeris and the American Ephemeris and Nautical Almanac
(Crown copyright 1961, fourth impression 1977) page 431 paragraph 3:

  "The chronological measure of time introduced in the sixteenth century by
  Josephus Justus Scaliger, under the name of the Julian period in honour
  of his father, strictly is a chronological cycle but practically is a
  continuous era.  It is a period of 7980 years, the least common multiple
  of the 28 year solar cycle, the 19 year lunar cycle and an ancient
  non-astronomical cycle of 15 years known as the cycle of the indiction.
  The epoch is the year when all three cycles began together, which was
  4713 B.C., ...",

Note that it was established in the sixteenth century, and has nothing to do
with the Julian calendar or with some biblical accounting of the creation of
the world.