Found in /System/Library/Perl/5.10.0/pods/perlfaq4.pod How can I find the Julian Day? (contributed by brian d foy and Dave Cross) You can use the "Time::JulianDay" module available on CPAN. Ensure that you really want to find a Julian day, though, as many people have different ideas about Julian days. See http://www.hermetic.ch/cal_stud/jdn.htm for instance. You can also try the "DateTime" module, which can convert a date/time to a Julian Day. $ perl −MDateTime −le'print DateTime−>today−>jd' 2453401.5 Or the modified Julian Day $ perl −MDateTime −le'print DateTime−>today−>mjd' 53401 Or even the day of the year (which is what some people think of as a Julian day) $ perl −MDateTime −le'print DateTime−>today−>doy' 30