Calendar converter.

[simonWMC2]

Hi. I want a page that works out what the Julian date is. There are lots of examples on the web, but all are a bit complicated. A good one is -

http://aa.usno.navy.mil/data/docs/JulianDate.html

However, all I want to do is work out the day, not the year. For example the 10 March would be day 069 (it is the 69th day of the year) I am assuming it is not a leap year.

I know i need to create a form where the user enters the date he /she wants converted and then use Javascript to do the conversion. I basically need the code to work out what month it is then add the days of all the previous month + the day of the current month. I would also like it to work the other way round, so the user can identify the real day from the Julian code.

I am getting quite confused, and if anyone could offer advice, I would be very happy

Thanx guys !

 

[dodge20]

Found this doing a google search, didn't test it though.

<SCRIPT LANGUAGE="JavaScript">
<!-- hide this script tag's contents from old browsers

function computeJD(formJD) {
    if (formJD.nmonth.value == "") {
      MM = 0
    } else {
      MM=eval(formJD.nmonth.value)
    }
    if (formJD.nday.value == "") {
      DD = 0
    } else {
      DD=eval(formJD.nday.value)
    }
    if (formJD.nyear.value == "") {
      YY = 0
    } else {
      YY=eval(formJD.nyear.value)
    }
    MM=eval(formJD.nmonth.value)
    DD=eval(formJD.nday.value)
    YY=eval(formJD.nyear.value)
    with (Math) {  
      GGG = 1;
      if (YY <= 1585) GGG = 0;
      JD = -1 * floor(7 * (floor((MM + 9) / 12) + YY) / 4);
      S = 1;
      if ((MM - 9)<0) S=-1;
      A = abs(MM - 9);
      J1 = floor(YY + S * floor(A / 7));
      J1 = -1 * floor((floor(J1 / 100) + 1) * 3 / 4);
      JD = JD + floor(275 * MM / 9) + DD + (GGG * J1);
      JD = JD + 1721027 + 2 * GGG + 367 * YY;
    }
    if (DD == 0 && MM == 0 && YY == 0) {
      alert("Please enter a meaningful date!")
    } else {
      formJD.JD.value = JD;
    }
}

function computeDJ(formDJ) {
  if (formDJ.JD.value == "") {
    alert("Please enter a meaningful Julian Day!")
    JD=0
  } else {
    JD=eval(formDJ.JD.value)
  }
  with (Math) {
    IJD = floor(JD);
    L = floor(IJD + 68569);
    N = floor(4 * L / 146097);
    L = L - floor((146097*N + 3)/4);
    I = floor(4000*(L + 1)/1461001);
    L = L - floor(1461 * I / 4) + 31;
    J = floor(80 * L / 2447);
    K = L - floor(2447 * J / 80);
    L = floor(J/11);
    J = J + 2 - 12*L;
    I = 100*(N - 49) + I + L;
  }
  if (JD != 0) {
    formDJ.nday.value = K;
    formDJ.nmonth.value = J;
    formDJ.nyear.value = I;
  }
}

function check_day(v) {
  if (v < 1 || v > 31 || v == "") {
    alert("Please enter a value for DAY in the 1-31 range or the result will be meaningless!")
    return ""
  } else {
    return true
  }
}

function check_month(v) {
  if (v < 1 || v > 12 || v == "") {
    alert("Please enter a value for MONTH in the 1-12 range or the result will be meaningless!")
    return ""
  } else {
    return true
  }
}
 
function check_year(v) {
  if (v <= 0 || v == "") {
    alert("Please enter a positive value for YEAR!")
    return ""
  } else {
    return true
  }
}

function check_JD(v) {
  if (v <= 0 || v == "") {
    alert("Please enter a positive value for Julian Day!")
    return ""
  } else {
    return true
  }
}

// done hiding from old browsers -->
</SCRIPT>

<FORM NAME=formJD>
Date (DD/MM/YYYY):
  <INPUT TYPE="text" NAME="nday"   Value="" SIZE=2
    ONCHANGE="check_day(this.value)"> /
  <INPUT TYPE="text" NAME="nmonth" Value="" SIZE=2
    ONCHANGE="check_month(this.value)"> /
  <INPUT TYPE="text" NAME="nyear"  Value="" SIZE=5>

<INPUT TYPE="button" VALUE="Corresponds to ->" OnClick="computeJD(this.form)">
<Br>

Julian Day : <INPUT TYPE="text" NAME="JD" Value="" SIZE=20>
</DL>

<INPUT TYPE="reset" Value="Reset Form">
</FORM>

<Hr align=center width=70%>

<DL>
<DT><B>JD to Date Conversion (JavaScript)</B>
<DD>
<FORM NAME=formDJ>
Julian Day : <INPUT TYPE="text" NAME="JD" Value="" SIZE=20
		ONCHANGE="check_JD(this.value)">

<INPUT TYPE="button" VALUE="Corresponds to ->" OnClick="computeDJ(this.form)">
<Br>

Date (DD/MM/YYYY):
  <INPUT TYPE="text" NAME="nday"   Value="" SIZE=2> /
  <INPUT TYPE="text" NAME="nmonth" Value="" SIZE=2> /
  <INPUT TYPE="text" NAME="nyear"  Value="" SIZE=5>

</DL>

<INPUT TYPE="reset" Value="Reset Form">
</FORM>

Dodge20