"Julian" ambiguity (was Re: [Python-Dev] strptime recapped)

[Steven Lott]

Thanks for the amplification - that was precisely my point.  
When proposing that strptime() parse "Julian" dates, some more
precise definition of Julian is required.


--- John Machin <sjmachin@lexicon.net> wrote:
> 21/06/2002 10:27:22 PM, Steven Lott <s_lott@yahoo.com> wrote:
> 
> >
> >Generally, "Julian" dates are really just the day number
> within
> >a given year; this is a simple special case of the more
> general
> >(and more useful) approach that R-D use.
> >
> >See
> >http://emr.cs.iit.edu/home/reingold/calendar-book/index.shtml
> >
> >for more information.
> >
> 
> AFAICT from perusing their book, R-D use the term
> "julian-date" to mean a tuple (year, month, day) in the Julian
> calendar.
> The International Astro. Union uses "Julian date" to mean an
> instant in time measured in days (and fraction therof) since
> noon on 1 January -4712 (Julian ("proleptic") calendar). See
> for example 
> http://maia.usno.navy.mil/iauc19/iaures.html#B1
> 
> A "Julian day number" (or "JDN") is generally used to mean an
> ordinal day number counting day 0 as Julian_calendar(-4712, 1,
> 1) as above. Some folks use JDN to include the IAU's
> instant-in-time.
> 
> Some folks use "julian day" to mean a day within a year (range
> 0-365 *or* 1-366 (all inclusive)). This terminology IMO should
> be severely deprecated. The concept is best described as
> something like "day of year", with a 
> specification of the origin (0 or 1) when appropriate. 
> 
> It is not clear from the first of your sentences quoted above
> exactly what you are calling a "Julian date": (a) the tuple
> (given_year, day_of_year) with calendar not specified or (b)
> just day_of_year. However either answer seems 
> IMO to be an inappropriate addition to the terminology
> confusion.
> 
> Cheers,
> John
> 
> 
> 
> 
> 
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=====
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S. Lott, CCP :-{)
S_LOTT@YAHOO.COM
http://www.mindspring.com/~slott1
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