Some Julian Day related verbs are available here:

http://www.jsoftware.com/jwiki/Scripts/JulianDayDate


--- PackRat wrote:

Just to put a plug in for the astronomical community, who obviously are
stakeholders when it comes to things related to time:

Please be sure to consult "Astronomical Algorithms" by Jean Meeus
(Willmann-Bell, 1998, 2nd ed.; 1991, 1st ed.).  Chapter 7 (at least in
the 1st ed.) deals with the fundamental day counter in astronomy,
namely, the Julian Day number--and this (and its reverse) is a
calculation that J should really have built into its dates.ijs script.
(There's also a Modified Julian Day number, which uses a more recent
date as its zero point--just as J uses 1/1/1800.)  By the way, the
Julian Day number is counted from 4713 B.C. (synchronized starting
point of several astronomical cycles) and is a completely different
thing than the similar-sounding Julian Date, which is the day number
within a year starting with January 1.  If you're doing any kind of
synchronicity of time series data (e.g., agricultural, financial, etc.)
with astronomical phenomena, the Julian Day number (and Modified Julian
Day) conversions are essential calculations.

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