One person wrote me privately the following. I consider it important enough
to respond publicly:

> <*insert appropriate pitches of voice*> Wirt, Wirt, Wirt, Wirt, Wirt, you
can'
>  just slip that past.  Since when would "Julian Date" be the same as
"Julian
> Day count"?  Surely a "Julian Date" would be the date off the Julian
Calendar.

That's one possible interpretation, and it would certainly be a very
reasonable interpretation, but that's not the interpetation that anyone uses.
The Julian Calendar, originated by Sosigenes and put into practice by Julius
Caesar, and later modified slightly by Augustus Caesar, as I said earlier,
unfortunately has nothing to do with Julian Dates.

The second web page that Howard Hoxie posted is an excellent recapitulation
of the history of Julian (and other closely related) Date numbering systems,
and I would recommend that everyone read it (in fact, I'm giving a test on
this material tomorrow night at 10PM EST):

     http://hermetic.magnet.ch/cal_stud/jdn.htm

As you'll see, the Julius of Julian Dates is no more closely related to
Julius Caesar as he is to Orange Julius'es :-).

Given the names, it's certainly understandable why there is so much
confusion, but the differences still must be distinguished.


>  I agree that the confusion needs to stop, but surely your parenthetical
> comment only adds to it.  Please don't argue that the term is used that
way,
> as the term *is* also used to refer to "date" created by concatenating the
year
> number with the day-of-year.  That doesn't make either correct (or maybe
> it does, depending on whether you are a descriptive or prescriptive
> linguist (and most folks are prescriptive on some things and descriptive
> on others)).

The "Julian Date" marked on all of the "Success" government calendars that
Walter Murray spoke of (and I had them on my desk too at Missile Flight
Safety and Nuclear Weapons Effects) is neither right nor wrong. Indeed, it's
not even on the same plane :-). As I said earlier, that date format is
nothing more than the concatenation of a Gregorian year with a DOY number and
it's inapplicable simultaneously to both the Julian Calendar and the Julian
Day Number -- and you can't do much better than that :-).

A Julian Date is the number of days from some arbitrary starting date,
nothing more, nothing less. However, because so many people have learned what
a "Julian Date" is wrongly, people have begun recently to describe Julian
Dates as a Julian Day Number. It's the same thing, but with the idea that
hopefully people will begin to use it properly.

As to calling a YYDDD format a "Julian Date," I really have no problem with
that other than the obivous one. I'm perfectly willing to an IBM PC a
Macintosh, or a Volkswagen Beetle a Ferrari, or even a Slider, whatever that
might be. The only reason that we agree on terms is for clarity of
comunication -- and the only way that we can maintain that clarity is to
defend with some vigor the original definitions of a term, regardless of what
the people at "Success" did to us all.

Wirt Atmar