// JavaScript Document
var rise; //globals (I know I'm lazy, but I know what I'm doing)
var latitude;
var TIME;
var RA_;
var t_;
var lngHour_;
var riseType;
var offset;

function dayOfYear(form)
{
 var N1, N2, N3;
 offset=parseFloat(form.offset.value);
 latitude=parseFloat(form.lat.value);
 
 if(form.riseType[0].checked)
 {
	 riseType=90.833333;
 }
 else if(form.riseType[1].checked)
 {
 	 riseType=96;
 }
 else if(form.riseType[2].checked)
 {
	 riseType = 102;
 }
 else 
 {
	 riseType = 108;
	 
 }
 
 
  N1 = Math.floor(275 * parseFloat(form.month.value) / 9.0);
  N2 = Math.floor((parseFloat(form.month.value) + 9) / 12.0);
  N3 = (1 + Math.floor((parseFloat(form.year.value) - 4 * Math.floor(parseFloat(form.year.value) / 4) + 2) / 3.0))
  N = N1 - (N2 * N3) + parseFloat(form.day.value) - 30;
  if(form.rise_set[0].checked){
    rise = 1;}
  else{
    rise=0;}
  hourValue(N, latitude, parseFloat(form.lon.value));
}//end dayOfYear

function hourValue(N, lat, lon)
{
 var lngHour;
 var t;
 lngHour = lon/15.0;
 lngHour_ = lngHour;//load global variable

 if(rise == 1){
   t = N + ((6 - lngHour) / 24.0);}
 else{
   t = N + ((18 - lngHour) / 24.0);}
 meanAnomaly(t);

}//end hourValue 

function meanAnomaly(t)
{
  var M;
  M= (0.9856 * t) - 3.289;
  t_ = t;//load global variable
  trueLongitude(M);

}

function trueLongitude(M)
{
  var L;
  L= M + (1.916 * Math.sin((3.1415265/180.0)*M)) + (0.020 * Math.sin((3.1415265/180.0)*2 * M)) + 282.634;
  if(L>360){
    while(L > 360)
    {
      L=L-360;
    }
  }
 
  if(L < 0){
   while(L < 0)
   {
    L = L + 360;
   }
  }
  rightAscension(L);

}//end true longitude

function rightAscension(L)
{
  var RA;
  RA = (180/3.1415265)*Math.atan(0.91764 * Math.tan((3.1415265/180)*L)) 
  
  if(RA>360){
    while(RA > 360)
    {
      RA=RA-360;
    }
  }
  if(RA < 0){
   while(RA < 0)
   {
    RA = RA + 360;
   }
  }
  adjustRightAscension(L, RA);

}//end rightAscension

function adjustRightAscension(L, RA)//L & RA need to be in same Cartesian quadrant
{
  var Lquadrant;
  var RAquadrant;
  Lquadrant  = (Math.floor( L/90.0)) * 90;
  RAquadrant = (Math.floor(RA/90.0)) * 90;
  RA = RA + (Lquadrant - RAquadrant);
  convert_RA_hours(RA, L);
}//end function

function convert_RA_hours(RA, L)
{
  RA = RA /15.0;
  RA_ = RA;//load global variable
  declination(L);
}

function declination(L)
{
  var sinDec;
  var cosDec;
  sinDec = 0.39782 * Math.sin((3.14159265/180.0)*L);
  cosDec = Math.cos((3.1415265/180)*(180/3.1415265)*Math.asin(sinDec));

 localHourAngle(cosDec, sinDec);
}

function localHourAngle(cosDec, sinDec)
{
  var cosH;
 cosH = (Math.cos((3.14159265/180.0)*riseType) - (sinDec * Math.sin((3.14159265/180.0)*latitude))) / (cosDec * Math.cos((3.14159265/180.0)*latitude));
  if (cosH >  1){
	  alert("The sun never rises on this location on the specified date");
	  return;
  }
  if (cosH < -1){
	  alert("The sun never sets on this location on the specified date");
	  return;
  }
  completeHourAngle(cosH);
}

function completeHourAngle(cosH)
{
 var H;
  
 if(rise==1)
  {
     H = 360 - (180/3.1415265)*Math.acos(cosH);
  }
  else
  {
     H = (180/3.1415265)*Math.acos(cosH);
  }
	
  H = H / 15.0;
  localMeanTime(H);

}

function localMeanTime(H)
{
 var T;
 var std;
 T = H + RA_ - (0.06571 * t_) - 6.622;

 UTC(T);

}

function UTC(T)
{
  var UT;
  var msg;
  var whole;
  var dec;
  var myTime;
  var min;
  UT = T - lngHour_;

  if(UT > 24)
  {
    while(UT > 24)
    {
      UT = UT -24;
    }
  }
  
  if(UT < 0)
  {
   while(UT < 0)
   {
     UT = UT + 24;
   }
  }

 std= UT + (offset);
if(std < 0)
{
 std = std + 24;
}

 whole= Math.floor(std);
 dec = std - whole;
 min = dec * 60;
 whole = Math.round(whole);
 
 if(whole < 10)
 {
	 whole = "0" + whole;
 }
 min = Math.round(min);
 
 if(min < 10)
 {
	 min = "0" + min;
 }

if(rise==1)
{ 
 msg="Sunrise will occur at: ";
}
else
{
 msg="Sunset will occur at: ";
}

alert(msg + whole + ":" + min + " Standard Time");

}//end UTC