What we (you, me, everyone in the JD Edwards universe) have always referred to as "Julian Date" is actual an Ordinal Date.
It is not, however, an ISO 8601 compliant Ordinal Date as ISO 8601 requires the use of 4 digit years.
The Julian Date is actually "...the interval of time in days and fractions of a day, since January 1, 4713 BC Greenwich noon, Julian proleptic calendar."
Do you suppose that 2454992.14583 ago, some guy was standing there with a sundial and said "Now!" to start the whole thing ticking?
Now you know...