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This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
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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:iece" module, part of the Standard Library,
which can convert a date/time to a Julian Day:

$ perl -MTime:iece -le 'print localtime->julian_day'
2455607.7959375

Or the modified Julian Day:

$ perl -MTime:iece -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:iece -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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