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Moon phase calculation
var MoonInfo = function(day, month, year) {
var n0 = parseInt( "0" );
var f0 = parseFloat( "0.0" );
var AG = f0; // Moon's age
var DI = f0; // Moon's distance in earth radii
var LA = f0; // Moon's ecliptic latitude
var LO = f0; // Moon's ecliptic longitude
var Phase = " ";
var Zodiac = " ";
// Related to month length and age calculations
var n28 = parseInt( "28" );
var n30 = parseInt( "30" );
var n31 = parseInt( "31" );
var dim = new Array( n31, n28, n31, n30, n31, n30, n31, n31, n30, n31, n30, n31 );
day = parseInt( day, 10 );
month = parseInt( month, 10 );
year = parseInt( year, 10 );
moon_posit( year, month, day );
this.age = round2( AG );
this.distance = round2( DI );
this.phase = Phase;
this.latitude = round2( LA );
this.longitude = round2( LO );
this.zodiac = Zodiac;
function isdayofmonth( y, m, d ) {
if( m != 2 ) {
if( 1 <= d && d <= dim[m-1] ) {
return true;
} else {
return false;
};
}
var feb = dim[1];
if( isleapyear( y ) ) feb += 1; // is leap year
if( 1 <= d && d <= feb ) return true;
return false;
}
function isleapyear( y ) {
var x = Math.floor( y - 4*Math.floor( y/4 ) );
var w = Math.floor( y - 100*Math.floor( y/100 ) );
var z = Math.floor( y - 400*Math.floor( y/400 ) );
if( x == 0 ) { // possible leap year
if( w == 0 && z != 0 ) {
return false; // not leap year
} else {
return true; // is leap year
};
}
return false;
}
// compute moon position and phase
function moon_posit( Y, M, D ) {
var YY = n0,
MM = n0,
K1 = n0,
K2 = n0,
K3 = n0,
JD = n0,
IP = f0,
DP = f0,
NP = f0,
RP = f0;
// calculate the Julian date at 12h UT
YY = Y - Math.floor( ( 12 - M ) / 10 );
MM = M + 9;
if( MM >= 12 ) MM = MM - 12;
K1 = Math.floor( 365.25 * ( YY + 4712 ) );
K2 = Math.floor( 30.6 * MM + 0.5 );
K3 = Math.floor( Math.floor( ( YY / 100 ) + 49 ) * 0.75 ) - 38;
JD = K1 + K2 + D + 59; // for dates in Julian calendar
if( JD > 2299160 ) JD = JD - K3; // for Gregorian calendar
// calculate moon's age in days
IP = normalize( ( JD - 2451550.1 ) / 29.530588853 );
AG = IP*29.53;
if( AG < 1.84566 ) Phase = "A new moon";
else if( AG < 5.53699 ) Phase = "An evening crescent";
else if( AG < 9.22831 ) Phase = "A first quarter";
else if( AG < 12.91963 ) Phase = "A waxing gibbous";
else if( AG < 16.61096 ) Phase = "A full moon";
else if( AG < 20.30228 ) Phase = "A waning gibbous";
else if( AG < 23.99361 ) Phase = "A Last quarter";
else if( AG < 27.68493 ) Phase = "A Morning crescent";
else Phase = "A new moon";
IP = IP*2*Math.PI; // Convert phase to radians
// calculate moon's distance
DP = 2*Math.PI*normalize( ( JD - 2451562.2 ) / 27.55454988 );
DI = 60.4 - 3.3*Math.cos( DP ) - 0.6*Math.cos( 2*IP - DP ) - 0.5*Math.cos( 2*IP );
// calculate moon's ecliptic latitude
NP = 2*Math.PI*normalize( ( JD - 2451565.2 ) / 27.212220817 );
LA = 5.1*Math.sin( NP );
// calculate moon's ecliptic longitude
RP = normalize( ( JD - 2451555.8 ) / 27.321582241 );
LO = 360*RP + 6.3*Math.sin( DP ) + 1.3*Math.sin( 2*IP - DP ) + 0.7*Math.sin( 2*IP );
// correcting if longitude is not greater than 360!
if ( LO > 360 ) LO = LO - 360;
}
// round to 2 decimal places
function round2( x )
{
return ( Math.round( 100*x )/100.0 );
}
// normalize values to range 0...1
function normalize( v )
{
v = v - Math.floor( v );
if( v < 0 )
v = v + 1;
return v;
}
if( !isdayofmonth( year, month, day ) ) {
alert( "Invalid date" );
return;
}
};
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