CFLib.org – Common Function Library Project

Description:
This function calculates the Julian Day for any date in the Gregorian calendar. Astronomers have used the Julian period to assign a unique number to every day since 1 January 4713 B.C.E. Julian Days begin at noon on the date specified.

Return Values:
Returns a numeric value.

Example:

<CFOUTPUT>Today's Julian Day is: #GetJulianDay()#</CFOUTPUT>

Parameters:

Full UDF Source:

/**
 * Calculates the Julian Day for any date in the Gregorian calendar.
 * 
 * @param TheDate      Date you want to return the Julian day for. 
 * @return Returns a numeric value. 
 * @author Beau A.C. Harbin (bharbin@figleaf.com) 
 * @version 1, September 4, 2001 
 */
function GetJulianDay(){
        var date = Now();    
    var year = 0;
    var month = 0;
    var day = 0;
    var hour = 0;
    var minute = 0;
    var second = 0;
    var a = 0;
    var y = 0;
    var m = 0;
    var JulianDay =0;
        if(ArrayLen(Arguments)) 
          date = Arguments[1];    
    // The Julian Day begins at noon so in order to calculate the date properly, one must subtract 12 hours
    date = DateAdd("h", -12, date);
    year = DatePart("yyyy", date);
    month = DatePart("m", date);
    day = DatePart("d", date);
    hour = DatePart("h", date);
    minute = DatePart("n", date);
    second = DatePart("s", date);
    
    a = (14-month) \ 12;
    y = (year+4800) - a;
    m = (month + (12*a)) - 3;
    
    JD = (day + ((153*m+2) \ 5) + (y*365) + (y \ 4) - (y \ 100) + (y \ 400)) - 32045;
    JDTime = NumberFormat(CreateTime(hour, minute, second), ".99999999");
    
    JulianDay = JD + JDTime;
    
    return JulianDay;
}