If the input xjd is a vector, then the outputs (yr,mn,day, and hr) will be vectors of the same length.Uses the algorithm of Fliegel and Van Flandern (1968) as reported in
the "Explanatory Supplement to the Astronomical Almanac" (1992), p. 604
Works for all Gregorian calendar dates with XJD > 0, i.e., dates after
-4713 November 23. Be sure that the Julian date is specified as double precision to maintain accuracy at the fractional hour level.
Other conversions and manipulations of Julian dates are provided by the CRAN packages chron and dates.