NAME

MoonPhase - Information about the phase of the moon

SYNOPSIS

use MoonPhase;

        ( $MoonPhase,
          $MoonIllum,
          $MoonAge,
          $MoonDist,
          $MoonAng,
          $SunDist,
          $SunAng ) = phase($seconds_since_1970);
        
        @phases  = phasehunt($seconds_since_1970);

DESCRIPTION

MoonPhase calculates information about the phase of the moon at a given time.

FUNCTIONS

phase()

        ( $MoonPhase,
          $MoonIllum,
          $MoonAge,
          $MoonDist,
          $MoonAng,
          $SunDist,
          $SunAng )  = phase($seconds_since_1970);

          $MoonPhase = phase($seconds_since_1970);

The argument is the time for which the phase is requested, expressed as a time returned by the time function. If $seconds_since_1970 is omitted, it does phase(time).

Return value in scalar context is $MoonPhase, the terminator phase angle as a percentage of a full circle (i.e., 0 to 1).

Return values in array context:

$MoonPhase:

the terminator phase angle as a percentage of a full circle (i.e., 0 to 1)

$MoonIllum:

the illuminated fraction of the Moon's disc

$MoonAge:

the Moon's age in days and fraction

$MoonDist:

the distance of the Moon from the centre of the Earth

$MoonAng:

the angular diameter subtended by the Moon as seen by an observer at the centre of the Earth.

$SunDist:

the distance from the Sun in km

$SunAng:

the angular size of Sun in degrees

Example:

   ( $MoonPhase,
     $MoonIllum,
     $MoonAge,
     $MoonDist,
     $MoonAng,
     $SunDist,
     $SunAng ) = phase();

     print "MoonPhase  = $MoonPhase\n";
     print "MoonIllum  = $MoonIllum\n";
     print "MoonAge    = $MoonAge\n";
     print "MoonDist   = $MoonDist\n";
     print "MoonAng    = $MoonAng\n";
     print "SunDist    = $SunDist\n";
     print "SunAng     = $SunAng\n";>

could print something like this:

     MoonPhase  = 0.598939375319023
     MoonIllum  = 0.906458030827876
     MoonAge    = 17.6870323368022
     MoonDist   = 372479.357420033
     MoonAng    = 0.534682403555093
     SunDist    = 152078368.820205
     SunAng     = 0.524434538105092

phasehunt()

     @phases = phasehunt($seconds_since_1970);

Finds time of phases of the moon which surround the given date. Five phases are found, starting and ending with the new moons which bound the current lunation.

The argument is the time, expressed as a time returned by the time function. If $seconds_since_1970 is omitted, it does phasehunt(time).

Example:

    @phases = phasehunt();
    print "New Moon      = ", scalar(localtime($phases[0])), "\n";
    print "First quarter = ", scalar(localtime($phases[1])), "\n";
    print "Full moon     = ", scalar(localtime($phases[2])), "\n";
    print "Last quarter  = ", scalar(localtime($phases[3])), "\n";
    print "New Moon      = ", scalar(localtime($phases[4])), "\n";

could print something like this:

    New Moon      = Wed Jun 24 06:51:47 1998
    First quarter = Wed Jul  1 21:42:19 1998
    Full moon     = Thu Jul  9 19:02:47 1998
    Last quarter  = Thu Jul 16 18:15:18 1998
    New Moon      = Thu Jul 23 16:45:01 1998

ABOUT THE ALGORITHMS

The algorithms used in this program to calculate the positions of Sun and Moon as seen from the Earth are given in the book Practical Astronomy With Your Calculator by Peter Duffett-Smith, Second Edition, Cambridge University Press, 1981. Ignore the word "Calculator" in the title; this is an essential reference if you're interested in developing software which calculates planetary positions, orbits, eclipses, and the like. If you're interested in pursuing such programming, you should also obtain:

Astronomical Formulae for Calculators by Jean Meeus, Third Edition, Willmann-Bell, 1985. A must-have.

Planetary Programs and Tables from -4000 to +2800 by Pierre Bretagnon and Jean-Louis Simon, Willmann-Bell, 1986. If you want the utmost (outside of JPL) accuracy for the planets, it's here.

Celestial BASIC by Eric Burgess, Revised Edition, Sybex, 1985. Very cookbook oriented, and many of the algorithms are hard to dig out of the turgid BASIC code, but you'll probably want it anyway.

Many of these references can be obtained from Willmann-Bell, P.O. Box 35025, Richmond, VA 23235, USA. Phone: (804) 320-7016. In addition to their own publications, they stock most of the standard references for mathematical and positional astronomy.

LICENCE

This program is in the public domain: "Do what thou wilt shall be the whole of the law".

AUTHORS

the moontool.c:

    A Moon for the Sun
    Release 2.0
    Designed and implemented by John Walker in December 1987,
    revised and updated in February of 1988.

Perl transcription:

    Raino Pikkarainen, 1998
    raino.pikkarainen@saunalahti.fi

cpanm Astro::MoonPhase

perl -MCPAN -e shell
install Astro::MoonPhase