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From: wyatt@cfa.UUCP
Newsgroups: comp.misc
Subject: Re: Julian date vs. the Julian calendar
Message-ID: <768@cfa.cfa.harvard.EDU>
Date: Thu, 12-Nov-87 12:52:49 EST
Article-I.D.: cfa.768
Posted: Thu Nov 12 12:52:49 1987
Date-Received: Sat, 14-Nov-87 13:48:50 EST
References: <2078@uvacs.CS.VIRGINIA.EDU>
Organization: Harvard-Smithsonian Ctr. for Astrophysics
Lines: 24

in article <2078@uvacs.CS.VIRGINIA.EDU>, rwl@uvacs.CS.VIRGINIA.EDU (Ray Lubinsky) says:
> Keywords: calendar systems
> 
> The Julian calendar system and the Julian date are two distinct time measures.
[...]
[correct info, ommitted for brevity.]
> 
> Scaliger calculated that these cycles coincided in the year 4317 B.C. so he
> started his system of reckoning on January 1, 4317 B.C.  As arbitrary as the
                                                ^^^^ typo! (4713)
> system is, it caught on in astronomy where dates can be given as an ordinal
> number (and fraction) of days from 0h UT January 0, 4317 B.C. [...]

Except that the zero point is Jan 1, 4713 B.C. at NOON (GMT). This 12-hour
offset is the source for the majority of JDN calculation errors. Before
1925, astronomers reckoned mean solar time from 12:00, hence the relic.

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