<<I must admit that I'm confused, Steve, particularly so about the
offset value of 50,448. Most people use January 1, 1900 as the start of
their Julian Date calendar, that being Day 1, although any date can be used,
so long as you're consistent. But if January 1, 1997 is to be 50,449, then
counting backwards, the reference date falls in the middle of the year 1858.
Why start there?>>


That's why I asked in the first reply if he wanted a "real" Julian or
Modified Julian date, as opposed to the day-of-year thing that so many
people erroneously call a "Julian" date.

For any given date/time, there's only one Julian Date; it is referenced from
noon, 1 January 4712BC using the Julian proleptic calendar (the name "Julian
date" has nothing to do with Emperor Julius Caesar, but the "Julian
proleptic calendar" is the one that he introduced). There's also exactly one
Modified Julian Date, which is referenced to midnight, November 17, 1858,
using the Gregorian calendar. MJD is a standard calculation use in
astronomy; in fact, the MJD start-date and calculation are recognized by the
International Astronomical Union and specified in CCIR Recommendation 457-1,
"USE OF THE MODIFIED JULIAN DATE BY THE STANDARD FREQUENCY AND TIME-SIGNAL
SERVICES". The start date is not negotiable, and calling anything
else-specifically the year-representation-plus-day-of-year thing-a "Julian"
date is a gross-but popular-error.

        <<Or is there an error lurking somewhere unseen in the algorithm?>>


I hope I transcribed it correctly, but I'm just as error-prone as anyone.

Steve