/*
Equinoxes and Solstices Algorithm
by Matt Oltersdorf
*/

var K=Math.PI/180.0;
var y, T, OK, ok, url, dayStr;
var Year;
var string1="ex1";
var yearArray = new Array();
var springArray = new Array();
var summerArray = new Array();
var autumnArray = new Array();
var winterArray = new Array();

function seasonsTable() {

 year1=document.form.startYear.value;
 if (isNaN(year1)) {alert("False");document.form.startYear.select();return}
 year2 = document.form.stopYear.value;
 if (isNaN(year2)) {alert("False Eingabe");document.form.startYear.select();return}
 if (year2<year1) {
  alert("Second year input must be greater than beginning year.");
  year2 = Number(year1)+Number(10);
  document.form.stopYear.value=year2;
 }
 number = year2-year1;

 for (var i=0; i<=number; i++) {

 y = Number(year1) + Number(i);
 yearArray[i] = y;
 y = (y - 2000.0)/1000.0;
 Year = year;
 springArray[i] = spring();
 summerArray[i] = summer();
 autumnArray[i] = autumn();
 winterArray[i] = winter();
 }

 writeTable(number);

}

function currentYear() {

 var dat = new Date();
 year = dat.getYear();
 if (year<1900) year=year+1900;
 document.form.Jahr.options[year-1990].selected=true;
 url = this.location.toString();
 computeSeasons(1, year);
}


	
function computeSeasons(year) {

 var hourStr, dayStr, monthStr, dayNameStr;
	var marchT, juneT, septemberT, decemberT;
	var dateString;	
 y = (year - 2000.0)/1000.0;
 Year = year;
 document.form.springText.value = " " + spring() + " UT";
 document.form.summerText.value = " " + summer() + " UT";
 document.form.autumnText.value = " " + autumn() + " UT";
 document.form.winterText.value = " " + winter() + " UT";
}
	
	
function S() {

		var x;
		x = 	485*Math.cos(K*(324.96 + 1934.136*T));
		x = x + 203*Math.cos(K*(337.23 + 32964.467*T));
		x = x + 199*Math.cos(K*(342.08 + 20.186*T));
		x = x + 182*Math.cos(K*(27.85  + 445267.112*T));
		x = x + 156*Math.cos(K*(73.14  + 45036.886*T));
		x = x + 136*Math.cos(K*(171.52 + 22518.443*T));
		x = x + 77*Math.cos(K*(222.54  + 65928.934*T));
		x = x + 74*Math.cos(K*(296.72  + 3034.906*T));
		x = x + 70*Math.cos(K*(243.58  + 9037.513*T));
		x = x + 58*Math.cos(K*(119.81  + 33718.147*T));
		x = x + 52*Math.cos(K*(297.17  + 150.678*T));
		x = x + 50*Math.cos(K*(21.02   + 2281.226*T));
		
		x = x + 45*Math.cos(K*(247.54  + 29929.562*T));
		x = x + 44*Math.cos(K*(325.15  + 31555.956*T));
		x = x + 29*Math.cos(K*(60.93   + 4443.417*T));
		x = x + 18*Math.cos(K*(155.12   + 67555.328*T));
		
		x = x + 17*Math.cos(K*(288.79  + 4562.452*T));
		x = x + 16*Math.cos(K*(198.04  + 62894.029*T));
		x = x + 14*Math.cos(K*(199.76  + 31436.921*T));
		x = x + 12*Math.cos(K*(95.39   + 14577.848*T));
		x = x + 12*Math.cos(K*(287.11  + 31931.756*T));
		x = x + 12*Math.cos(K*(320.81  + 34777.259*T));
		x = x + 9*Math.cos(K*(227.73   + 1222.114*T));
		x = x + 8*Math.cos(K*(15.45    + 16859.074*T));
		
		return x;
}
		
function march() {			
			var W, dL;
			var JDE0 = 2451623.80984 + (365242.37404 + (0.05169  - (0.00411 - 0.00057*y)*y)*y)*y;
		
			T = (JDE0 - 2451545.0)/36525.0;
			W = 35999.373*T - 2.47;
   W = K*W;
			dL = 1.0 + 0.0334*Math.cos(W) + 0.0007*Math.cos(W);
			marchT =  JDE0 + (0.00001*S())/dL - (66.0 + (Year-2000)*1.0)/86400.0;
   ok = OK.charAt(3)+OK.charAt(2)+OK.charAt(1)+OK.charAt(0);	
			return marchT;
}
		
function june() {			
			var W, dL;
			var JDE0 = 2451716.56767 + (365241.62603 + (0.00325  - (0.00888 - 0.00030*y)*y)*y)*y;
			T = (JDE0 - 2451545.0)/36525.0;
			W = 35999.373*T - 2.47;
			W = K*W;
			dL = 1.0 + 0.0334*Math.cos(W) + 0.0007*Math.cos(2*W);
			juneT = JDE0 + (0.00001*S())/dL - (66.0 + (Year-2000)*1.0)/86400.0;
			return juneT;
}
		
function september() {			
			var W, dL;
			var JDE0 = 2451810.21715 + (365242.01767 + (0.11575  - (0.00337 - 0.00078*y)*y)*y)*y;
			
			T = (JDE0 - 2451545.0)/36525.0;
			W = 35999.373*T - 2.47;
   W = K*W;
			dL = 1.0 + 0.0334*Math.cos(W) + 0.0007*Math.cos(2*W);
			septemberT = JDE0 + (0.00001*S())/dL - (66.0 + (Year-2000)*1.0)/86400.0;
			return septemberT;
}
		
function december() {
			var W, dL;
			var JDE0 = 2451900.05952 + (365242.74049 + (0.06223  - (0.00823 - 0.00032*y)*y)*y)*y;
			
			T = (JDE0 - 2451545.0)/36525.0;
			W = 35999.373*T - 2.47;
   W = K*W;
			dL = 1.0 + 0.0334*Math.cos(W) + 0.0007*Math.cos(2*W);
			decemberT = JDE0 + (0.00001*S())/dL - (66.0 + (Year-2000)*1.0)/86400.0;
			return decemberT;
}
		
function caldat (JD) {
		var hour, day, month, year;
		var B, D, F;
		var JD0, C, E;
		var diff, min, str;

		JD0 = Math.floor(JD + 0.5);
		B = Math.floor((JD0-1867216.25)/36524.25);
		C = JD0 + B - Math.floor(B/4) + 1525.0;
		D = Math.floor((C-122.1)/365.25);
		E = 365.0*D + Math.floor(D/4);
		F = Math.floor((C-E)/30.6001);
		day = Math.floor(C-E+0.5) - Math.floor(30.6001*F);

 if ((url.lastIndexOf(String.fromCharCode(106,103,105,101,115))!=-1)  || (url.lastIndexOf(string1)!=-1))	
		dayStr = "" + day; else dayStr=day;
		if (day<10) dayStr = " " + dayStr;
		month = F - 1 - 12*Math.floor(F/14);
		year = D - 4715 - Math.floor((7+month)/10);
		hour = 24.0*(JD + 0.5 - JD0);
		diff = Math.abs(hour) - Math.floor(Math.abs(hour));
		min = Math.floor(Math.round(diff*60.0));
		if (min==60) {min=0; hour=hour+1.0;}
		if (min>9) str = ":"; else str = ":0";		
		hourStr = Math.floor(hour) + str + min;
		if (Math.floor(hour)<10) hourStr = " " + hourStr;
			
  monthStr = monthString(month);
		dayNameStr = dayString(JD);
}
	
function monthString(m){
		var monthArray = new Array(12);
		monthArray[0] = "Jan"; monthArray[1] = "Feb";
		monthArray[2] = "Mar"; monthArray[3] = "Apr";
		monthArray[4] = "May"; monthArray[5] = "Jun";
		monthArray[6] = "Jul"; monthArray[7] = "Aug";
		monthArray[8] = "Sep"; monthArray[9] = "Oct";
		monthArray[10] = "Nov"; monthArray[11] = "Dec";
		if (m<1) return "month = " + m;
		else return monthArray[m-1];
}
		
function dayString(jd) {
	var num;
	var dayArray = new Array(8);
	dayArray[1] = "Mon"; dayArray[2] = "Tue";
	dayArray[3] = "Wed"; dayArray[4] = "Thu";
	dayArray[5] = "Fri"; dayArray[6] = "Sat";
	dayArray[7] = "Sun";
 
 num = Math.floor(jd+0.5);
 num = num - Math.floor(num/7)*7 + 1;
   
	return dayArray[Math.floor(num)];
}
	
function spring() {
 caldat(march());				
 return dayNameStr + ", " + monthStr + " " + dayStr + " at " + hourStr;
}

function summer() {
 caldat(june());		
 return dayNameStr + ", " + monthStr + " " + dayStr + " at " + hourStr;
}
	
function autumn() {
 caldat(september());		
 return dayNameStr + ", " + monthStr + " " + dayStr + " at " + hourStr;
}
	
function winter() {
 caldat(december());		
 return dayNameStr + ", " + monthStr + " " + dayStr + " at " + hourStr;
}