Date-MSD

 view release on metacpan or  search on metacpan

README  view on Meta::CPAN

NAME

Date::MSD - conversion between flavours of Mars Sol Date

DESCRIPTION

For date and time calculations it is convenient to represent dates by
a simple linear count of days, rather than in a particular calendar.
This module performs conversions between different flavours of linear
count of Martian solar days ("sols").

Among Martian day count systems there are also some non-trivial
differences of concept.  There are systems that count only complete days,
and those that count fractional days also.  There are some that are fixed
to Airy Mean Time (time on the Martian prime meridian), and others that
are interpreted according to a timezone.  The functions of this module
appropriately handle the semantics of all the non-trivial conversions.

lib/Date/MSD.pm  view on Meta::CPAN

    $msd = js_to_msd($js);
    ($cmsdn, $cmsdf) = msd_to_cmsdnf($msd, $tz);
    $js = cmsdn_to_js($cmsdn, $cmsdf, $tz);

    # and 69 other conversion functions

=head1 DESCRIPTION

For date and time calculations it is convenient to represent dates by
a simple linear count of days, rather than in a particular calendar.
This module performs conversions between different flavours of linear
count of Martian solar days ("sols").

Among Martian day count systems there are also some non-trivial
differences of concept.  There are systems that count only complete days,
and those that count fractional days also.  There are some that are fixed
to Airy Mean Time (time on the Martian prime meridian), and others that
are interpreted according to a timezone.  The functions of this module
appropriately handle the semantics of all the non-trivial conversions.

lib/Date/MSD.pm  view on Meta::CPAN

Number") which is a count of complete days since the same epoch.  XYZN is
the integral part of XYZ.  There is also a quantity named "XYZF" ("XYZ
Fraction") which is a count of fractional days since the XYZN changed
(at midnight).  XYZF is the fractional part of XYZ, in the range [0, 1).

This quantity naming pattern is derived from the naming of Terran day
counts, particularly JD (Julian Date) and JDN (Julian Day Number) which
have the described correspondence.  The "XYZF" name type is a neologism,
invented for L<Date::JD>.

All calendar dates given are in the Darian calendar for Mars.  An hour
number is appended to each date, separated by a "T"; hour 00 is midnight
at the start of the day.  An appended "Z" indicates that the date is to
be interpreted in the timezone of the prime meridian (Airy Mean Time),
and so is absolute; where any other timezone is to be used then this is
explicitly noted.

=over

=item MSD (Mars Sol Date)

lib/Date/MSD.pm  view on Meta::CPAN

coincidence of midnight on the Martian prime meridian with noon
on the Terran prime meridian.  MSD is defined by the paper at
L<http://pubs.giss.nasa.gov/docs/2000/2000_Allison_McEwen.pdf>.

=item JS (Julian Sol)

days elapsed since 0000-01-01T00Z (MSD -94129.0) (approximately
MJD -91195.22 in Terrestrial Time).  This epoch is an Airy
midnight approximating the last northward equinox prior to
the first telescopic observations of Mars.  The same epoch is
used for the Darian calendar for Mars.  JS is defined (but not
explicitly) by the document describing the Darian calendar, at
L<http://pweb.jps.net/~tgangale/mars/converter/calendar_clock.htm>.

=item CMSD (Chronological Mars Solar Date)

days elapsed since -0608-23-20T00 in the timezone of interest.
CMSD = MSD + 500000.0 + Zoff, where Zoff is the timezone
offset in fractional days.  CMSD is defined by the memo at
L<http://www.fysh.org/~zefram/time/define_cmsd.txt>.

=back