FAQ 4.16 How can I find the Julian Day?

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4.16: How can I find the Julian Day?

    (contributed by brian d foy and Dave Cross)

    You can use the "Time::Piece" module, part of the Standard Library,
    which can convert a date/time to a Julian Day:

            $ perl -MTime::Piece -le 'print localtime->julian_day'

    Or the modified Julian Day:

            $ perl -MTime::Piece -le 'print localtime->mjd'

    Or even the day of the year (which is what some people think of as a
    Julian day):

            $ perl -MTime::Piece -le 'print localtime->yday'

    You can also do the same things with the "DateTime" module:

            $ perl -MDateTime -le'print DateTime->today->jd'
            $ perl -MDateTime -le'print DateTime->today->mjd'
            $ perl -MDateTime -le'print DateTime->today->doy'

    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):

            $  perl -MTime::JulianDay -le 'print local_julian_day( time )'


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