
<!-- Hide from browsers that do not support JavaScript
//
//     Moon-phase calculation
//     Roger W. Sinnott, Sky & Telescope, June 16, 2006.
//
var jd=0
//
// ---------------------------------------------------------------------
//
function setup() {
  var nowdate = new Date();
  var day = nowdate.getDate();
  var month = nowdate.getMonth();
  var year = nowdate.getFullYear();
  document.moonfaseBox.yearf.value = year;
  document.moonfaseBox.monthf.selectedIndex = month;
  document.moonfaseBox.dayf.selectedIndex = day - 1;
  }
//
// ---------------------------------------------------------------------
//
function proper_ang(big)
{
with (Math)
{
var tmp = 0;
if (big > 0)
{
tmp = big / 360.0;
tmp = (tmp - floor(tmp)) * 360.0;
}
else
{
tmp = ceil(abs(big / 360.0));
tmp = big + tmp * 360.0;
}
}
return tmp;
}
//
// ---------------------------------------------------------------------
//
function daysInFebruary (year) {
  if (year > 1582) {
     return (((year % 4 == 0) && ( (!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28 );
     }
  else {
     return ((year % 4 == 0) ? 29 : 28 );
  }
}  
//
// ---------------------------------------------------------------------
// 
function DaysArray(n)
{
for (var i = 1; i <= n; i++)
{
this[i] = 31
if (i==4 || i==6 || i==9 || i==11) {this[i] = 30}
if (i==2) {this[i] = 29}
} 
return this;
}
// 
// ---------------------------------------------------------------------
// 
function isDate()
{
var daysInMonth = DaysArray(12)
var monthIdx = document.moonfaseBox.monthf.selectedIndex;
var month = eval(document.moonfaseBox.monthf.options[monthIdx].value);
var dayIdx = document.moonfaseBox.dayf.selectedIndex;
var day = eval(document.moonfaseBox.dayf.options[dayIdx].value);
var yearff = document.moonfaseBox.yearf.value

if (yearff == "") {
   alert("Please enter the year.");
   document.moonfaseBox.yearf.focus();
   return false;
   }

if (isNaN(yearff)) {
   alert("Please reenter the year.  Only numbers are allowed.");
   document.moonfaseBox.yearf.focus();
   return false;
   }

var year = eval(yearff)

if (year == 0) {
   alert("Sorry!  There was no year 0 in common reckoning.  Please enter 1 and click 'BC' if that is what you meant.")
   document.moonfaseBox.yearf.focus();
   return false;
   }

if (year < 0 ) {
  alert("Sorry!  Don't use a minus sign with the year.  Instead, click 'BC' and increase the absolute value of the year by one.")
  document.moonfaseBox.yearf.focus();
  return false;
  }

var eraObj = document.getElementsByName("adbc");
    for (var i = 0; i < eraObj.length; i++) {
          if (eraObj[i].checked) {
            era = eraObj[i].value;
            }
       }
    if (era == 0) year = 1 - year

// Note:  From here on, in this function only, 'year' is the astronomical year with sign!! 
if (month == 2 && day == 29 && day > daysInFebruary(year)) {
  alert("Sorry!  Not a leap year, so there is no February 29th.")
  return false;
  }

if (day > daysInMonth[month]) {
  alert("Oops!  Please enter a valid number for the day.")
  return false;
  }

if (year==1582 && month==10 && day>4 && day<15) {
  alert("Invalid date.  In the Gregorian calendar reform, October 4, 1582, was immediately followed by October 15, 1582.")
  return false;
  }

if (year < -3999) {
  alert("The year you've entered is too early.  Please enter a year after 4001 BC.")
  return false;
  }

if (year > 8000) {
  alert("The year you've entered is too far in the future.  Please enter a year prior to AD 8001.")
  return false;
  }

if ((year < 100) && (year > 0)) {
  alert("Caution!  You've entered a year prior to AD 100.  If you intended a modern date, be sure 'AD' is clicked and enter all four digits of the year.  If you really did mean an early historical date in the Julian calendar, the Moon's phase will be correctly shown.")
  }

return true;
}
// 
// ---------------------------------------------------------------------
// 
function ValidateForm()
{
if (isDate()==false) return false
jdn()
moonElong()
return true
}
//
// ---------------------------------------------------------------------
//
function jdn() {
  var now_date = new Date();
  zone = now_date.getTimezoneOffset() / 1440;

  var monthIdx = document.moonfaseBox.monthf.selectedIndex;
  var mm = eval(document.moonfaseBox.monthf.options[monthIdx].value);

  var dayIdx = document.moonfaseBox.dayf.selectedIndex;
  var dd = eval(document.moonfaseBox.dayf.options[dayIdx].value);

  var yy = eval(document.moonfaseBox.yearf.value);
     with (Math) {
     var yyy=yy;
     var eraObj = document.getElementsByName("adbc");
          for (var i = 0; i < eraObj.length; i++) {
               if (eraObj[i].checked) {
                  era = eraObj[i].value;
               }
            }
         if (era == 0) yyy = 1 - yy
     var mmm = mm;
     if (mm < 3) {
       yyy = yyy - 1;
       mmm = mm + 12;
       }
     var day = dd + zone + 0.5;
     var a = floor(yyy/100);
     var b = 2 - a + floor(a/4);
     jd = floor(365.25*yyy) + floor(30.6001*(mmm+1)) + day + 1720994.5;
     if (jd > 2299160.4999999) jd = jd + b;
     }
     // document.moonfaseBox.jdnum.value = jd;
}
//
// ---------------------------------------------------------------------
//
function moonElong() {
   with (Math) {
   var dr = PI / 180
   var rd = 1 / dr 
   var meeDT = pow((jd - 2382148), 2) / (41048480*86400)
   var meeT = (jd + meeDT - 2451545.0) / 36525
   var meeT2 = pow(meeT,2)
   var meeT3 = pow(meeT,3)
   var meeD = 297.85 + (445267.1115*meeT) - (0.0016300*meeT2) + (meeT3/545868)
       meeD = proper_ang(meeD) * dr
   var meeM1 = 134.96 + (477198.8676*meeT) + (0.0089970*meeT2) + (meeT3/69699)
       meeM1 = proper_ang(meeM1) * dr
   var meeM = 357.53 + (35999.0503*meeT)
       meeM = proper_ang(meeM) * dr
   var elong = meeD*rd + 6.29*sin(meeM1)
       elong = elong   - 2.10*sin(meeM)
       elong = elong   + 1.27*sin(2*meeD - meeM1)
       elong = elong   + 0.66*sin(2*meeD)
       elong = proper_ang(elong)
       elong = round(elong)
   var moonNum = ((elong + 6.43) / 360) * 28
       moonNum = floor(moonNum)
       if (moonNum == 28) moonNum = 0
       if (moonNum < 10) moonNum = "0" + moonNum
   var moonImage = "http://www.demodemo.ws/calculators/moon/images/moon" + moonNum.toString() + ".gif"
   }
   var moonPhase = " 0% - New Moon"
     if ((moonNum>03) && (moonNum<11)) moonPhase = " First Quarter"
     if ((moonNum>10) && (moonNum<18)) moonPhase = " Full Moon"
     if ((moonNum>17) && (moonNum<25)) moonPhase = " Last Quarter"
  
  

if ((moonNum==01)||(moonNum==27)) {
           moonPhase = "6.25%"
           }
if ((moonNum==02)||(moonNum==26)) {
           moonPhase = "12.5%"
           }
if ((moonNum==03)) {
           moonPhase = "18.75%"
           }
if ((moonNum==04)) {
           moonPhase = "Waxing Cresent"
           }
if ((moonNum==05)||(moonNum==24)) {
           moonPhase = "31.25%"
           }
if ((moonNum==06)||(moonNum==23)) {
           moonPhase = "37.5%"
           }
if ((moonNum==08)||(moonNum==20)) {
           moonPhase = "56.25%"
           }
if ((moonNum==09)) {
           moonPhase = "62.5%"
           }
if ((moonNum==10)||(moonNum==19)) {
           moonPhase = "68.75%"
           }
if ((moonNum==11)) {
           moonPhase = "Waxing Gibbous"
           }
if ((moonNum==12)||(moonNum==17)) {
           moonPhase = "81.25%"
           }
if ((moonNum==16)) {
           moonPhase = "87.5%"
           }
if ((moonNum==15)||(moonNum==13)) {
           moonPhase = "93.75%"
           }


if ((moonNum==18)) {
           moonPhase = "Wanning Gibbous"
           }


if ((moonNum==22)) {
           moonPhase = "43.75%"
           }


if ((moonNum==25)) {
           moonPhase = "Wanning Cresent"
           }


   
  document.moonfaseBox.moonphasetext.value = moonPhase   
  document.slideshow.src = moonImage
  // document.moonfaseBox.elongation.value = elong

var huntTime = " Best Time to Hunt"
if ((moonNum==0)||(moonNum==01)||(moonNum==02)||(moonNum==13)||(moonNum==14)||(moonNum==15)||(moonNum==16)||(moonNum==26)||(moonNum==27)) {
           huntTime = "AM/PM/Midday"}
if ((moonNum==03)||(moonNum==04)||(moonNum==05)||(moonNum==06)||(moonNum==07)||(moonNum==08)||(moonNum==09)||(moonNum==10)||(moonNum==17)||(moonNum==07)||(moonNum==18)||(moonNum==19)||(moonNum==20)||(moonNum==21)||(moonNum==22)||(moonNum==23)) {
           huntTime = "PM"}
if ((moonNum==24)||(moonNum==25)) {
           huntTime = "AM/PM"}
if ((moonNum==11)||(moonNum==12)) {
	   huntTime = "PM/Midday"}

document.moonfaseBox.huntTimetext.value = huntTime

var huntRate = " Hunt Rating"
if((moonNum==13)||(moonNum==14)||(moonNum==15)) {
	huntRate = "Excellent"}
if((moonNum==0)||(moonNum==01)||(moonNum==02)||(moonNum==16)||(moonNum==17)||(moonNum==18)||(moonNum==26)||(moonNum==27)) {
	huntRate = "Very Good"}
if((moonNum==03)||(moonNum==04)||(moonNum==05)||(moonNum==06)||(moonNum==09)||(moonNum==10)||(moonNum==11)||(moonNum==12)||(moonNum==19)||(moonNum==23)||(moonNum==24)||(moonNum==25)) {
	huntRate = "Good"}
if((moonNum==07)||(moonNum==08)||(moonNum==20)||(moonNum==21)||(moonNum==22)) {
	huntRate = "Fair"}
document.moonfaseBox.huntRatetext.value = huntRate


var huntRateColor = ""

if((moonNum==13)||(moonNum==14)||(moonNum==15)) {huntRateColor = document.getElementById("huntRatetext").style.backgroundColor="#006600"}

if((moonNum==0)||(moonNum==01)||(moonNum==02)||(moonNum==16)||(moonNum==17)||(moonNum==18)||(moonNum==26)||(moonNum==27)) {huntRateColor = document.getElementById("huntRatetext").style.backgroundColor="#9999ff"} 

if((moonNum==03)||(moonNum==04)||(moonNum==05)||(moonNum==06)||(moonNum==09)||(moonNum==10)||(moonNum==11)||(moonNum==12)||(moonNum==19)||(moonNum==23)||(moonNum==24)||(moonNum==25))
{huntRateColor = document.getElementById("huntRatetext").style.backgroundColor="#6600cc"}

if((moonNum==07)||(moonNum==08)||(moonNum==20)||(moonNum==21)||(moonNum==22))
{huntRateColor = document.getElementById("huntRatetext").style.backgroundColor="#ff0000"}

document.moonfaseBox.huntRatetext.style.backgroundColor = huntRateColor

var huntTimeColor = ""

if((moonNum==0)||(moonNum==01)||(moonNum==02)||(moonNum==13)||(moonNum==14)||(moonNum==15)||(moonNum==16)||(moonNum==26)||(moonNum==27))
{huntTimeColor = document.getElementById("huntTimetext").style.backgroundColor="#006699"}

if((moonNum==03)||(moonNum==04)||(moonNum==05)||(moonNum==06)||(moonNum==07)||(moonNum==08)||(moonNum==09)||(moonNum==10)||(moonNum==17)||(moonNum==07)||(moonNum==18)||(moonNum==19)||(moonNum==20)||(moonNum==21)||(moonNum==22)||(moonNum==23))
{huntTimeColor = document.getElementById("huntTimetext").style.backgroundColor="#66cccc"}

if((moonNum==24)||(moonNum==25))
{huntTimeColor = document.getElementById("huntTimetext").style.backgroundColor="#666600"}

if((moonNum==11)||(moonNum==12))
{huntTimeColor = document.getElementById("huntTimetext").style.backgroundColor="#ffcc00"}

document.moonfaseBox.huntTimetext.style.backgroundColor = huntTimeColor

}

// Finish hiding
-->