Re: FTP Format

I was rather surprised to see my name coming up in this thread, but it
would be more accurate to say my wife has forbidden me from participating
in social discussions of "this calendar stuff" when it comes up (and
obviously for me to never introduce the topic). Of any party of N attendees
there will generally be one person (initially) fascinated by a historical
review of the topic, and wanting to continue the discussion, while (N-1)
attendees have their patience very much tested and simply desire that we
rapidly move on to another topic :)

Bruce

On Sat, Nov 19, 2011 at 1:26 PM, Vern Hamberg <vhamberg@xxxxxxxxxxx> wrote:

I find this calendar stuff interesting - but such an interest led to the
real expert, Bruce Vining, from being invited to parties, so he says.

But we are rather stuck with what we have - for some reason lost in
recent history, IBM uses *JUL for a way to represent dates within a
given year - maybe because it is something like the real julian date, as
you've described it.

So I think there is little benefit to fighting city hall in these things
- but it is maybe useful to know the difference of context, in order not
to be embarrassed when talking in other groups, such as astrophysicists
- have any of us been to one of their meetings recentlyl?

I did look up a name I remember - Scaliger - J.J. Scaliger is the person
who originally proposed the use of the so-called Julian date - well, let
the following quote say it -

The number of days since noon on January 1, -4712, i.e., January 1, 4713
BC <http://scienceworld.wolfram.com/astronomy/BC.html> (Seidelmann
1992). It was proposed by J. J. Scaliger
<http://scienceworld.wolfram.com/biography/Scaliger.html> Eric
Weisstein's World of Biography in 1583, so the name for this system
derived from Julius Scaliger
<http://scienceworld.wolfram.com/biography/Scaliger.html>, Eric
Weisstein's World of Biography not Julius Caesar.

So this has nothing whatsoever to do with the Julian calendar -
something I didn't know, and I won't make that mistake again!

Apparently Scaliger went back using 3 calendar systems to find a date
where they coincided - more details at
http://scienceworld.wolfram.com/astronomy/JulianDate.html

So I guess if we want to be exhaustively clear, we need to distinguish
between astronomical, Roman, and IBM Julian dates.

Isn't the English language the most fun of all?

Regards
Vern


On 11/17/2011 4:55 PM, John Yeung wrote:

On Thu, Nov 17, 2011 at 3:40 PM, CRPence<CRPbottle@xxxxxxxxx> wrote:

On 15-Nov-2011 22:13 , John Yeung wrote:

IBM's "Julian dates" have as much to do with *actual* Julian
dates as Julian Lennon.

Most references to a "Julian date" [for IBM i anyhow]
likely apply only to a presentation-format and\or input-
format for Gregorian date values.

This is my point exactly. There is no reason for that *format* to be
called Julian, because there is no relationship between that format
and any variation on the Julian date system. Even the astronomical
Julian date system (a) uses the Julian calendar, and (b) is a number
of days from a single fixed point in all of time, not from the
beginning of EACH year.

Did Julius Caesar express dates as a year and a number of days from
the beginning of that year? No. He used 12 months, and days within
the month, just like we do today. So where does "Julian format" come
from?

The terminology was even worse at my previous job. There, "Julian
date" specifically meant YYDDD, "extended Julian date" meant YYYYDDD,
"Gregorian date" meant YYYYMMDD, and "calendar date" meant MMDDYY.

the database [AFaIK still] only supports the Gregorian
calendar [though, with the skipped\missing days
accounted\included] for date calculations.

First of all, there would be no useful reason to support anything
other than the Gregorian calendar. It's what the entire world uses,
at least when interacting internationally. (There are religious,
cultural, and local calendar systems that may be used internally by
those religions, cultures, or localities.)

Second, I'm not completely sure what you mean by skipped/missing days.
Are you referring to the point at which England switched from the
Julian calendar to the Gregorian, and thus had to enact a one-time
correction? Unless you are a historian and your data actually uses
dates from that time (and keep in mind that different areas of the
world switched to Gregorian at different times; Russia was still using
the Julian calendar until 1918!), it really only makes sense to do all
calculations as if the Gregorian calendar had always been in effect.
(And this is what the IBM-supplied functions do.)

I will say this: I have seen a lot of home-grown date code that
calculates as if the Julian calendar were in effect! (Specifically,
any code that assumes *every* 4th year is a leap year is effectively
using the Julian calendar, and not the Gregorian calendar.)

John Y.

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