FAQ 4.16 How can I find the Julian Day?

Discussion in 'Perl Misc' started by PerlFAQ Server, Feb 24, 2011.

  1. This is an excerpt from the latest version perlfaq4.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    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'
    2455607.7959375

    Or the modified Julian Day:

    $ perl -MTime::piece -le 'print localtime->mjd'
    55607.2961226851

    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'
    45

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

    $ perl -MDateTime -le'print DateTime->today->jd'
    2453401.5
    $ perl -MDateTime -le'print DateTime->today->mjd'
    53401
    $ perl -MDateTime -le'print DateTime->today->doy'
    31

    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 )'
    55608



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    PerlFAQ Server, Feb 24, 2011
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