DateTime::Astro(3)

NAME
DateTime::Astro - Functions For Astromical Calendars

DESCRIPTION
DateTime::Astro implements functions used in astronomical calendars, such as calculation of lunar longitudea and solar longitude.

This module is best used in environments where a C compiler and the MPFR arbitrary precision math library is installed. It can fallback to using Math::BigInt, but that would pretty much render it useless because of its speed and loss of accuracy that may creep up while doing Perl to C struct conversions.

DISCLAIMER
This module works, but there are several caveats you should be aware of:

  MPFR Is Required / PurePerl Version Not Functional
There /is/ a HALF BAKED Pure Perl implmentation bundled with this distribution, but at this point please consider it UNUSABLE. This sort of calculation requires the speed and efficiency of a C library anyway.

As such, you HAVE to have MPFR installed correctly in your system. Please consult your local package manager, or http://mpfr.org

Patches to make the pure perl version work better is always welcome.

  17 solar terms are still off by ~ 5 minutes
I've tried very hard to correctly calculate the solar term dates with this module, but I still get 17 instances in about 130 years worth of solar terms, where the dates are off by an average of about 5 minutes -- and these usually fall at right about midnight, causing day-based comparisons to be off by 1.

I'm sure there's something that's causing a round off somwhere. If you're up to it, please see xt/101_solar_terms.t and see if you can fix it for me!

FUNCTIONS

  BACKEND()
Returns 'XS' or 'PP', noting the current backend.

  dt_from_moment($moment)
Given a moment (days since rd + fractional seconds), returns a DateTime object in UTC

  dynamical_moment($moment)
Computes the moment value from given moemnt, taking into account the ephemeris correction.

  dynamical_moment_from_dt($dt)
Computes the moment value from a DateTime object, taking into account the ephemeris correction.

  ephemeris_correction($moment)
Computes the ephemeris correction on a given moment

  gregorian_components_from_rd($rd_days)
Computes year, month, date from RD value

  gregorian_year_from_rd($rd_days)
Computes year from RD value

  julian_centuries($dt)
Computes the julian centuries for given DateTime object

  julian_centuries_from_moment($moment)
Computes the julian centuries for given moment

  lunar_phase($dt)
Computes the lunar phase for given DateTime object

  lunar_phase_from_moment($moment)
Computes the lunar phase for given moment

  polynomial($x, ...)
Computes the polynomical expression using $x as the variable. The left most argument is the constant, and each successive argument is the coefficient for the next power of $x

  ymd_seconds_from_moment($moment)
Computes the gregorian components (year, month, day) from the RD date, and the number of seconds from the fractional part.

  lunar_longitude($dt)
Returns the Moon's longitude on the given date $dt

  lunar_longitude_from_moment($moment)
Returns the Moon's longitude on the given moment $moment

  moment($dt)
Returns the date $dt expressed in moment

  nth_new_moon($n)
Returns the $n-th new moon, in $moment.

Currently the new moons dates are accurate to about within +/- 60 seconds of the actual new moon for modern dates.

For older dates, the accuraccy degrades a bit to about +/- 5 minutes.

  new_moon_after($dt)

  new_moon_before($dt)

  solar_longitude($dt)
Returns the Sun's longitude on the given date $dt

  solar_longitude_from_moment($moment)
Returns the Sun's longitude on the given moment $moment

  new_moon_after_from_moment

  new_moon_before_from_moment

  solar_longitude_after

  solar_longitude_after_from_moment

  solar_longitude_before

  solar_longitude_before_from_moment

CONSTANTS

  MEAN_SYNODIC_MONTH
Mean time (in moment) between new moons

  MEAN_TROPICAL_YEAR
Mean time (in moment) between a full year (time for the Earth to go around the sun)

LICENSE
This library is available under Artistic License v2, and is:

    Copyright (C) 2012  Daisuke Maki C<< <daisuke@endeworks.jp> >>

AUTHOR
Daisuke Maki "<daisuke@endeworks.jp>"