moonphase(3)

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 termina
tor 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 = $MoonPhase0;
print "MoonIllum = $MoonIllum0;
print "MoonAge = $MoonAge0;
print "MoonDist = $MoonDist0;
print "MoonAng = $MoonAng0;
print "SunDist = $SunDist0;
print "SunAng = $SunAng0;>

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($phas

es[0])), "0;
print "First quarter = ", scalar(localtime($phas

es[1])), "0;
print "Full moon = ", scalar(localtime($phas

es[2])), "0;
print "Last quarter = ", scalar(localtime($phas

es[3])), "0;
print "New Moon = ", scalar(localtime($phas

es[4])), "0;

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 posi
tions 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 Uni versity 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) accu
racy 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 Will
mann-Bell, P.O. Box 35025, Richmond, VA 23235, USA.
Phone: (804) 320-7016. In addition to their own publica
tions, 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

perl v5.8.0 2000-01-20 MoonPhase(3)