Question

I am trying to find a free API that provides lunar phase predictions including moonrise and moonset. My PHP based tide tables application is using NOAA for tide and weather data, but it doesn’t seem like they offer any lunar data. Does Google have this built into one of their API’s that I just don’t know about?

On the off chance that nobody knows of a free API (preferably government provided), does anybody know of a simple way to calculate this? I’ve seen this post, but the solutions are attempting to calculate them with a high degree of precision. If it’s off by a little bit, it’s fine.

Answer 1

You can calculate it yourself easily enough

• http://www.phpclasses.org/package/1201-PHP-Calculates-the-phase-of-the-Moon.html
• http://jivebay.com/calculating-the-moon-phase/

Taken from wxforums.net, posting by “Cristian”

<?php
/*
Adaptation en php du fameux et excellent scripte Astro-MoonPhase de Brett Hamilton écrit en Perl.
http://search.cpan.org/~brett/Astro-MoonPhase-0.60/

Ce Scripte vous permettra de connaître, à une date donnée, l'illumination de la Lune, son age, 
sa distance en km par rapport à la Terre, son angle en degrés, sa distance par rapport au soleil, 
et son angle par rapport au soleil.

*/
class Moon
     {
     function phase($Year, $Month, $Day, $Hour, $Minutes, $Seconds)
         {
         $DateSec = mktime($Hour, $Minutes, $Seconds, $Month, $Day, $Year, 0);

         ini_set(precision, "20");   //Defini la precision des calcules

         # Astronomical constants.
         $Epoch                  = 2444238.5;        # 1980 January 0.0

         # Constants defining the Sun's apparent orbit.
         $Elonge                     = 278.833540;       # ecliptic longitude of the Sun at epoch 1980.0
         $Elongp                     = 282.596403;       # ecliptic longitude of the Sun at perigee
         $Eccent                     = 0.016718;             # eccentricity of Earth's orbit
         $Sunsmax                = 1.495985e8;       # semi-major axis of Earth's orbit, km
         $Sunangsiz              = 0.533128;             # sun's angular size, degrees, at semi-major axis distance

         # Elements of the Moon's orbit, epoch 1980.0.
         $Mmlong                     = 64.975464;        # moon's mean longitude at the epoch
         $Mmlongp                = 349.383063;       # mean longitude of the perigee at the epoch
         $Mlnode                     = 151.950429;       # mean longitude of the node at the epoch
         $Minc                   = 5.145396;             # inclination of the Moon's orbit
         $Mecc                   = 0.054900;             # eccentricity of the Moon's orbit
         $Mangsiz                = 0.5181;           # moon's angular size at distance a from Earth
         $Msmax                  = 384401.0;             # semi-major axis of Moon's orbit in km
         $Mparallax              = 0.9507;           # parallax at distance a from Earth
         $Synmonth               = 29.53058868;      # synodic month (new Moon to new Moon)

         $pdate = Moon::jtime($DateSec);

         $pphase;                # illuminated fraction
         $mage;                  # age of moon in days
         $dist;                  # distance in kilometres
         $angdia;                # angular diameter in degrees
         $sudist;                # distance to Sun
         $suangdia;              # sun's angular diameter


         # Calculation of the Sun's position.

         $Day = $pdate - $Epoch;                                         # date within epoch
         $N = Moon::fixangle((360 / 365.2422) * $Day);               # mean anomaly of the Sun
         $M = Moon::fixangle($N + $Elonge - $Elongp);                # convert from perigee
                                         # co-ordinates to epoch 1980.0
         $Ec = Moon::kepler($M, $Eccent);                            # solve equation of Kepler
         $Ec = sqrt((1 + $Eccent) / (1 - $Eccent)) * tan($Ec / 2);
         $Ec = 2 * Moon::todeg(atan($Ec));                           # true anomaly
         $Lambdasun = Moon::fixangle($Ec + $Elongp);                     # Sun's geocentric ecliptic
                                         # longitude
         # Orbital distance factor.
         $F = ((1 + $Eccent * cos(Moon::torad($Ec))) / (1 - $Eccent * $Eccent));
         $SunDist = $Sunsmax / $F;                                   # distance to Sun in km
         $SunAng = $F * $Sunangsiz;                                  # Sun's angular size in degrees


         # Calculation of the Moon's position.

         # Moon's mean longitude.
         $ml = Moon::fixangle(13.1763966 * $Day + $Mmlong);

         # Moon's mean anomaly.
         $MM = Moon::fixangle($ml - 0.1114041 * $Day - $Mmlongp);

         # Moon's ascending node mean longitude.
         $MN = Moon::fixangle($Mlnode - 0.0529539 * $Day);

         # Evection.
         $Ev = 1.2739 * sin(Moon::torad(2 * ($ml - $Lambdasun) - $MM));

         # Annual equation.
         $Ae = 0.1858 * sin(Moon::torad($M));

         # Correction term.
         $A3 = 0.37 * sin(Moon::torad($M));

         # Corrected anomaly.
         $MmP = $MM + $Ev - $Ae - $A3;

         # Correction for the equation of the centre.
         $mEc = 6.2886 * sin(Moon::torad($MmP));

         # Another correction term.
         $A4 = 0.214 * sin(Moon::torad(2 * $MmP));

         # Corrected longitude.
         $lP = $ml + $Ev + $mEc - $Ae + $A4;

         # Variation.
         $V = 0.6583 * sin(Moon::torad(2 * ($lP - $Lambdasun)));

         # True longitude.
         $lPP = $lP + $V;

         # Corrected longitude of the node.
         $NP = $MN - 0.16 * sin(Moon::torad($M));

         # Y inclination coordinate.
         $y = sin(Moon::torad($lPP - $NP)) * cos(Moon::torad($Minc));

         # X inclination coordinate.
         $x = cos(Moon::torad($lPP - $NP));

         # Ecliptic longitude.
         $Lambdamoon = Moon::todeg(atan2($y, $x));
         $Lambdamoon += $NP;

         # Ecliptic latitude.
         $BetaM = Moon::todeg(asin(sin(Moon::torad($lPP - $NP)) * sin(Moon::torad($Minc))));

         # Calculation of the phase of the Moon.

         # Age of the Moon in degrees.
         $MoonAge = $lPP - $Lambdasun;

         # Phase of the Moon.
         $MoonPhase = (1 - cos(Moon::torad($MoonAge))) / 2;

         # Calculate distance of moon from the centre of the Earth.

         $MoonDist = ($Msmax * (1 - $Mecc * $Mecc)) /
             (1 + $Mecc * cos(Moon::torad($MmP + $mEc)));

         # Calculate Moon's angular diameter.

         $MoonDFrac = $MoonDist / $Msmax;
         $MoonAng = $Mangsiz / $MoonDFrac;

         # Calculate Moon's parallax.

         $MoonPar = $Mparallax / $MoonDFrac;

         $pphase = $MoonPhase;                                   # illuminated fraction
         $mage = $Synmonth * (Moon::fixangle($MoonAge) / 360.0);     # age of moon in days
         $dist = $MoonDist;                                      # distance in kilometres
         $angdia = $MoonAng;                                         # angular diameter in degrees
         $sudist = $SunDist;                                         # distance to Sun
         $suangdia = $SunAng;                                    # sun's angular diameter
         $mpfrac = Moon::fixangle($MoonAge) / 360.0;
         return array( $pphase, $mage, $dist, $angdia, $sudist, $suangdia, $mpfrac, $mpfrac );
         }

     function fixangle($x)   { return ($x - 360.0 * (floor($x / 360.0))); }  # fix angle
     function torad($x)  { return ($x * (M_PI / 180.0)); }               # deg->rad
     function todeg($x)  { return ($x * (180.0 / M_PI)); }               # rad->deg

     function jtime($t)
         {
         $julian = ($t / 86400) + 2440587.5;     # (seconds /(seconds per day)) + julian date of epoch       2440587.5 / 86400 = 28,24753472222 Days
         return ($julian);
         }

     function kepler($m, $ecc)
         {
         $EPSILON = 1e-6;

         $m = Moon::torad($m);
         $e = $m;
         while (abs($delta) > $EPSILON)
             {
             $delta = $e - $ecc * sin($e) - $m;
             $e -= $delta / (1 - $ecc * cos($e));
             }
         return ($e);
         }

     }


 //Exemple d'utilisation :

//Pour le 11 Avril 2009 à 00h00
list($MoonPhase, $MoonAge, $MoonDist, $MoonAng, $SunDist, $SunAng, $mpfrac) = Moon::phase(2009, 04, 11, 00, 00, 01);
echo "La Lune est éclairée à ".number_format($MoonPhase*100, 2, ',', '')."%"."<br>";
echo "Son age est de ".number_format($MoonAge, 0, ',', '')." jours"."<br>";
echo "Et elle se situe à une distance de ".number_format($MoonDist, 0, ',', '')." km par rapport à la Terre."."<br>";
?>